Category Archives: Medical Entomology

6 Things to Know About The Asian Giant Hornet

Asian giant hornets have hit the news recently, sometimes going by the name of “murder hornets”.  Below are six key things to know about these insects and the situation in North America:


1) What is the Asian Giant Hornet?
The Asian giant hornet (Vespa mandarinia), which is also known as the “great sparrow bee” in its native range (or recently sensationalized as the “murder hornet”) is a wasp species native to parts of southern and eastern Asia. The Asian giant hornet is amongst the world’s largest wasps, with queens approaching a length of 2 inches (typically ~1.5 inches). Workers and males are smaller, but still measure over an inch long. Asian giant hornets have a distinctive appearance with a bright yellowish-orange head, a dark body, and alternating dark and yellowish stripes on the gaster (“abdomen”). This species creates subterranean nests, which commonly have a peak workforce of around 100 workers.

A distinctive Asian giant hornet adult. Photo Credit: Washington State Dept. Agriculture, Bugwood.org

Asian giant hornets pose threats as an invasive species in North America. These insects are efficient predators with complex hunting behaviors. While Asian giant hornets prey upon a wide range of insects, they are capable of attacking honey bees. Under the right conditions, Asian giant hornets can decimate hives of European honey bees (Apis mellifera) within a few hours.  Their potent stings can also pose medical concerns for humans.


2) What’s the risk in the Midwest?
Based on the current situation, the risk from Asian giant hornets in Wisconsin and the Midwestern US is extremely low. To date, Asian giant hornets have never been found in Wisconsin or surrounding states. A very small number of Asian giant hornets were spotted in southwestern British Columbia and northwestern Washington state in the second half of 2019. For Wisconsin, these sightings have been roughly 1,500 miles from us. At the time this article was written (early May 2020), Asian giant hornets had not been spotted in North America in 2020. Update 5/27: we recently learned that AGHs have made it through the winter in North America.  This species recently resurfaced, as reported in the New York TimesDespite this recent finding, all confirmed sightings of the AGH are from the Pacific Northwest and these insects pose little risk for the Midwest at this time.


3) What’s the timeline of the Asian giant hornet story?
Asian giant hornets have gotten a lot of attention in the news recently, but these stories really missed the main “action”, which occurred roughly half a year ago. (Imagine if Sport Illustrated took half a year to write about the Super Bowl’s winning team!). The story of the Asian giant hornet in North America began in August of 2019 when a beekeeper in Nanaimo, British Columbia (SE Vancouver Island) spotted these wasps. Three specimens were collected at the time and their identity was confirmed.

Also in August of 2019, a beekeeper in Northern Bellingham, Washington (US) observed Asian giant hornets, but no specimens were collected. Back in Nanaimo, British Columbia, an Asian giant hornet nest was located and eradicated in an urban park (Robin’s Park) in September. A month later (late October, 2019) a specimen was photographed in nearby mainland British Columbia (White Rock, BC). Around that time, the same beekeeper in Northern Bellingham, Washington observed Asian giant hornets attacking a hive. The last sighting of the Asian giant hornet occurred near Blaine, Washington in December of 2019, when a dead specimen was collected and a live specimen was spotted at a hummingbird feeder.

Update June, 2020: Small numbers of AGHs have been reported in North America—but only in the pacific Northwest. 


4) Have Asian giant hornets become established in North America?
The ability of the Asian giant hornet to survive and spread in North America is not understood at this time. In its native range, the Asian giant hornet is associated with forested and low mountainous areas with temperate or subtropical climates.  A key unanswered question at the moment is: have the Asian giant hornets successfully overwintered in North America? Update 5/27: we recently learned that AGHs have made it through the winter.  This species recently resurfaced, as reported in the New York Times.

Asian giant hornets overwinter as queens.  If previously fertilized, queens attempt to establish nests during the spring months. Established nests won’t produce the next batch of queens to carry on their “blood lines” until mid-fall, meaning that responders monitoring the situation in the Pacific northwest will have roughly half a year to hunt down any nests. For this reason, 2020 will be a critical “make or break” year in the story of the Asian giant hornet in North America.

Responders in the Pacific Northwest have plans to monitor for Asian giant hornets with traps and visual methods. If spotted, individual hornets can potentially be tracked back to their nest to allow responders to eradicate the colonies. Full details of the USDA response plan can be viewed here.


5) Health risks to humans are low
By referring to the Asian giant hornet as “murder hornets”, recent news stories have given the false impression that these insects pose a regular threat to humans. Many stories have repeated the claim that Asian giant hornets kill around 50 people a year in Japan, where these hornets naturally occur. In reality, the actual numbers are much lower. Based on publicly available data from the Japanese e-Stat statistics portal, from 2009-2018 an average of 18 deaths were reported annually in Japan from hornets, wasps, and bees combined. For comparative purposes, roughly twice as many annual deaths (average of 35) were reported as the result of slipping and drowning in bathtubs over that same period of time.

Annual Deaths in Japan due to hornets, wasps and bees. Data source: Japan e-State website (https://www.e-stat.go.jp/en)

Nonetheless, Asian giant hornets do have potent venom and 1/4 inch-long stingers, which pack a punch.  Due to their large physical size, a relatively large volume of venom can be injected leading to painful stings. If many stings occur (such as if one were to disrupt a nest), medical attention is advised.


6) Are there any look-alikes?
While we don’t have Asian giant hornets in Wisconsin or the Midwest, we have plenty of other insects that are currently being mistaken for the Asian giant hornet or could be mistaken for these hornets later this year. Panicked individuals thinking they’ve found an Asian giant hornet might end up killing native, beneficial insects which pose little risk to humans—such as bumble bee queens, which are currently trying to establish their nests for the year.

Historically, the UW Insect Diagnostic Lab receives many suspected reports of Asian giant hornets every year—all of these have been misidentifications by the submitters. To date, no confirmed sightings of the Asian giant hornet have occurred in Wisconsin or the Midwestern US. However, with the media spotlight on the Asian giant hornet, an increase in false reports is expected at the UW Insect Diagnostic Lab this year.  Click the diagram below to view a

Asian giant hornets and common look-alikes of the Midwest. Diagram organized by PJ Liesch, UW Insect Diagnostic Lab. Click for larger version.

full-size version.

 

Some of the commonest look-alikes include:

Cicada Killer Wasps (Sphecius speciosus) These are the closest match in terms of size. However, these solitary ground-nesting wasps are really quite harmless, unless you happen to be a cicada... Because these insects don’t have a colony to defend, they are very unlikely to sting.  This is the top look-alike reported to the UW Insect Diagnostic Lab every year. For additional details see this post: Asian Giant Hornets—Nope!

Great Golden Digger Wasps (Sphex ichneumoneus) These solitary ground nesting wasps capture and feed katydids and related insects to their young.  Because these insects don’t have a colony to defend, they tend to be docile.

Pigeon Horntails (Tremex columba) These primitive wasp-like insects develop inside of decaying trees as larvae and can be common.  They are not capable of stinging, but females do possess a prominent egg-laying structure (ovipositor).

Elm Sawflies (Cimbex americana) These plump, wasp-like insects cannot sting. The caterpillar-like larvae can feed on elms, willows, birches, and other hardwood trees.

Bumble Bees (Bombus spp.) The Midwest is home to over 20 species of bumble bees. These beneficial pollinators play important roles in the ecosystem. Bumble bees do live together as colonies and can act defensively if the nest is directly disturbed, but these important pollinators are generally docile. Annual colonies reach maximum size in late summer and naturally die out in the fall.

Yellowjackets (Vespula spp. & Dolichovespula spp.) The Midwest is home to more than 10 species of yellowjackets. Common species, such as the German yellowjacket (Vespula germanica) are typically around ½ inch in length. Yellowjackets are social insects and depending on the species, nests can occur in the ground, in hollow voids (such as soffit overhangs or wall voids), or as exposed as papier-mâché type aerial nests. Annual colonies reach maximum size in late summer and die out naturally in the fall.

Bald-Faced Hornets (Dolichovespula maculata) Our largest social wasp in the Midwestern US, reaching lengths of approximately ¾ inch. Bald-faced hornets are technically a type of “yellowjacket” but have a distinctive black and white appearance. These insects create large papier-mâché type nests, which can approach the size of a basketball. Annual colonies reach maximum size in late summer and die out in the fall.

Blister Beetles—Unexpected Wisconsin Connections

Despite being winter, Wisconsin has recently been in the news because of insects—blister beetles—and their potentially deadly impacts on horses.  In addition to their medical significance, these insects have a long and interesting story with some surprising twists.

Margined blister beetle (Epicauta funebris). Photo credit: Johnny N. Dell, Bugwood.org.

Blister beetles comprise a diverse family of insects (Family Meloidae), with over 3,000 species known from around the globe. In the Unites States, we’ve got approximately 400 species, with the bulk of the diversity centered in the dry southwestern part of the country. However, this group is widely distributed across the lower 48 states, with nearly 30 species known from Wisconsin alone.

The common blister beetles species of the Upper Midwest are oblong and typically range from ½-inch to ¾-inch long, although other species can vary in size. Unlike the stereotypical “crunch” of most other beetles—think of accidentally stepping on a May/June beetle—blister beetles have softer bodies and are similar to fireflies in this regard. A few of our Midwestern species are striped or brightly colored, but many common species are dark-colored, being mostly black, grey, or a dark metallic green.

But don’t let their drab appearance fool you. Blister beetles wield a potent defensive toxin—cantharidin. In adult blister beetles, this compound is produced by males, which provide it to females during courtship. Females then use it to chemically protect their eggs.

An antique apothecary jar hints at the long medical history of cantharidin. Photo Credit: Hamburg Museum, via Wikipedia

The properties of cantharidin are well-known, and this chemical irritant and its coleopteran source have a surprising history dating back thousands of years. For example, Pliny the Elder knew of the toxic effects and mentioned blister beetles in his writings. Old medical reference books list a number of potential uses for cantharidin, ranging from the treatment of skin conditions to a supposed remedy for baldness. However, cantharidin might have harmed more than it helped. Dermal exposure has long been known to cause irritation and blistering—hence the common name of “blister beetles”. If ingested, symptoms can be much more serious: severe irritation of the gastrointestinal and urinary tracts, kidney and heart damage, and a cascade of other undesirable effects. Human deaths have been recorded in the medical literature and in a recent report, a soldier consumed a single blister beetle on a dare and ended up hospitalized with acute kidney injury.

Surprisingly, cantharidin was also historically deployed as an aphrodisiac—Spanish fly. In the days before the little blue pill, Spanish fly was known for its ability to irritate the urethral lining to produce a “stimulating” effect.  In one historical report, French Legionnaires in North Africa complained of priapism after feasting upon frogs that had happened to eat blister beetles (frogs seem to be unaffected by cantharidin).

Humans aren’t the only creatures affected by blister beetles and horses are especially sensitive. Ingestion of only a few grams of cantharidin can potentially be lethal to an adult horse. Blister beetle poisoning is rare in equines, but can occur if the adult beetles happen to be in an alfalfa field feeding on blossoms at the time of harvest and are crushed by farm equipment. In an unfortunate situation, blister beetles have recently been reported in connection with the deaths of over a dozen horses in Mauston, Wisconsin.

Robert “Fighting Bob” La Follette, governor of Wisconsin (1901-1906), was known for his progressive politics and impressive head of hair. Photo via Wikimedia Commons

Blister beetles have another noteworthy Wisconsin connection from the history books. The former governor of Wisconsin, Robert “Fighting Bob” La Follette, was well-known for his progressive politics as well as an impressive head of hair. His secret?—a hair tonic containing cologne, oils of English lavender and rosemary, and a cantharidin-containing tincture made from blister beetles.

Beetlejuice on the brain?

5 Things to Know About Eastern Equine Encephalitis

Every year is different when it comes to mosquito-borne diseases.  During the summer and fall of 2019, the eastern US has seen a bump in cases of a potentially lethal disease—Eastern Equine Encephalitis (EEE)—which has led to health concerns. Here are five key things to know about Eastern Equine Encephalitis:


1. Eastern Equine Encephalitis is a mosquito-borne disease. But one species in particular, Culiseta melanura, plays a critical role.  Culiseta melanura is widely distributed across the eastern US, but is specifically associated with freshwater swamps with standing trees.  The larvae of this mosquito tend to develop in small, protected, naturally occurring cavities (“crypts”) amongst the roots of trees such as maple, hemlock, and cedar.  Interestingly, Culiseta melanura, does not like to bite humans and almost exclusively takes blood meals from birds.  However, as EEE builds up in local bird populations, other mosquito species with more flexible feeding habits can act as a “bridge” and allow the disease to move from birds to mammals with subsequent blood meals.  A dozen or more mosquito species from the genera Aedes, Coquillettidia, Culex, and Ochlerotatus have been implicated in vectoring the disease from birds to humans.

The mosquito Culiseta melanura
Culiseta melanura—a key player in the Eastern Equine Encephalitis story. Photo Credit: CDC Public Health Image Library.

2. Eastern Equine Encephalitis can pose significant risks to human health, but most human infections result in minor or no symptoms.  Eastern Equine Encephalitis is a disease caused by a virus (the Eastern Equine Encephalitis Virus).  According to the CDC, only a small percentage (4-5%) of human infections with this virus actually lead to Eastern Equine Encephalitis.  Thus, the vast majority of human infections lead to minor or no symptoms. 

However, in severe cases of EEE, inflammation of the brain can lead to symptoms including fever, headache, vomiting, confusion, convulsions, and coma.  Roughly a third of such human cases are fatal and survivors often suffer from permanent neurological complications.  Individuals younger than 15 or older than 50 are at greatest risk, as well as individuals that live, work, or recreate near swampy areas. In the US, cases of EEE tend to occur in states along the Atlantic coast and the Gulf coast.  The New England states of Connecticut, Massachusetts, and Rhode Island have seen nearly 20 human EEE cases this year.  Cases can also occur in the Midwest, with a cluster of nearly a dozen reports in southwestern Michigan and northern Indiana in 2019.

3. Humans aren’t the only species impacted by Eastern Equine Encephalitis.  In fact, EEE is primarily a bird disease.  For example, many passerine birds (a group that includes our common songbirds such as robins and starlings) can readily become infected with the EEE virus. Some states even use “sentinel” birds to monitor EEE activity.  If the conditions are right in a given year, populations of the ornithophilic mosquito Culiseta melanura can cause EEE to build up in a local bird population.  Eventually, other mosquito species allow the disease to jump from birds to humans.  Horses can also become infected with the EEE virus and because equine infections typically precede human cases by a few weeks, an uptick in horse cases can serve as a general indicator of potential risk to humans in an area.  There is a vaccine available for horses to help protect them from EEE.

Cedar swamp in New Jersey.
Cedar swamp in New Jersey. Photo Credit: Famartin, via Wikipedia. CC 3.0.

4. Eastern Equine Encephalitis is very rare in humans.  Case numbers vary around the eastern US every year, but over the last decade the country has averaged only seven human EEE cases per year.  In Wisconsin, there have only been three documented human cases of EEE between 1964 and 2018.  The limited habitat of the key mosquito species and its restricted feeding behaviours help explain the rarity of human cases.  Despite news reports within the last month, the EEE threat should nearly be done for the year in the Upper Midwest.  Eastern Equine Encephalitis cases typically peak in late summer or early autumn, and with temperatures dipping in the region (and snow in the forecast), mosquito activity is on the decline in our area.

5. General mosquito precautions are one of the simplest ways to protect against Eastern Equine Encephalitis.  Because the key mosquito species involved with EEE (Culiseta melanura) is associated with freshwater swamps, chemical insecticide treatments to such areas are often not an option for individual land owners and can pose environmental concerns.  Instead, practices such as wearing long-sleeved clothing, using EPA-registered repellents (such as DEET and picaridin), avoiding areas and periods of high mosquito activity, and removing standing water on a property are some of the best precautions to take.


Update September 2020: Wisconsin has recently had two confirmed human cases this year.

Masked Hunter Bugs: Another Kissing Bug Look-Alike

“I think I’ve found a kissing bug and wanted to report it” is a surprisingly common line I get at the UW Insect Diagnostic Lab.

I’ve previously written about kissing bugs, but to quickly recap: these are blood-feeding assassin bugs found primarily in South and Central America.  Kissing bugs tend to be associated with vertebrate nests outdoors but can bite humans and can also carry Trypanosoma cruzia parasite that causes Chagas disease.  Due to this concern, I see a spike in website traffic and “reports” of suspected kissing bugs just about any time there’s national news coverage of these insects. While many kissing bug species exist, the vast majority are restricted to tropical and subtropical areas.  The northernmost species—the eastern conenose kissing bug (Triatoma sanguisuga)—ranges from Latin America as far north as southern Illinois.

Eastern conenose kissing bug adult.
Eastern conenose kissing bug adult. Photo credit: Robert Webster, via Wikipedia

Insects don’t care for geopolitical boundaries, but when humans shade in the entire state of Illinois on a distribution map of kissing bugs, it gives the false impression that these insects are on the tollway marching towards Wisconsin’s southern border.  However, the eastern conenose kissing bug is rarely spotted in the northern parts of its range and there has never been a verified case of kissing bugs from within Wisconsin.

The regular occurrence of false reports can likely be attributed to hype in the news combined with a good ol’ case of mistaken identity.  It turns out that there are a number of common insects that can resemble kissing bugs.  One of these, the western conifer seed bug (Leptoglossus occidentalis), is regularly encountered in the upper Midwest because these insects sneak indoors in the fall just like boxelder bugs.  Recently, the commonest look-alike I’ve been getting reports of is the masked hunter bug (Reduvius personatus), which can also be encountered indoors.

If you aren’t familiar with masked hunter bugs, there’s a good reason why these insects can sometimes mistaken for kissing bugs—they’re technically kissing cousins.  Both kissing bugs and masked hunter bugs belong to the assassin bug family (Family Reduviidae).  This is a diverse family of approximately 7,000 species worldwide and we have dozens of common species in the Midwest.  The vast majority of these species (including masked hunter bugs) are really beneficial predators of other arthropods and are of little medical importance.  In theory, if you picked up and mishandled one of our Midwestern assassin bugs species, it could bite—likely feeling similar to a wasp sting—although that’s about the worst it could do.

Juvenile masked hunter bug camouflaged with debris.
Juvenile masked hunter bug camouflaged with debris. Photo Credit: Chiswick Chap, via Wikipedia

Masked hunter bugs are readily identifiable, although the nymphs (juveniles) can have you scratching your head if you haven’t encountered them before.  The nymphs are often ¼” – ½” long and camouflage themselves with bits of lint and other debris—as a result, they can resemble miniature walking dust bunnies.  Once you recognize this disguise, they’re easy to identify.

Masked Hunter Bug Adult.
Masked Hunter Bug Adult. Photo credit: JP Hamon, via wikipedia

Adult masked hunter bugs are slender, roughly ¾” long, and entirely dark coloured.  They have long, thin legs & antennae and stout beak-like mouthparts which they use to feed on insects and other arthropod prey.  Several key features help distinguish masked hunter bugs from eastern conenose kissing bugs:

  1. Masked hunter bugs are entirely dark while eastern conenose kissing bugs have red on their body
  2. Masked hunter bugs lack the projecting “conenose” present on the head of kissing bugs
  3. Masked hunter bugs have a bulging, “muscular” appearance of their prothorax (trapezoidal region behind the head) when viewed under magnification
  4. Masked hunter bugs have stout beak-like mouthparts while kissing bugs have long, slender mouthparts when viewed under magnification

Side-by-side comparison of a kissing bug and a masked hunter bug.
Side-by-side comparison of a kissing bug and a masked hunter bug. Photo Credit: Devon Pierret and PJ Liesch, UW Insect Diagnostic Lab. [Click for full sized version]
When it comes to kissing bugs, we simply don’t have these insects in the Upper Midwest, but we do have look-alikes.  For side-by-side diagrams showing an eastern conenose kissing bug compared to common look-alikes, visit the ID Guide page on this website: insectlab.russell.wisc.edu/visual-id-guides/

Black Flies: Out for Blood in the Midwest

Mosquito season has officially kicked off in Wisconsin, meaning the omnipresence of repellents for the foreseeable future.  If mosquitoes have redeeming properties, it’s that they at least serve as food for a wide variety of animals and can even act as pollinators in some cases.  When mosquitoes bite, they do so with surgical precision that would make a phlebotomist green with envy.  Simply reading about mosquitoes might make you feel itchy, although on the spectrum of biting flies, things could be much more sinister…

Also very active at the moment in Wisconsin are black flies (Family Simuliidae) and our state is home to 30 species of these tiny sanguivores.  Black flies—or “buffalo gnats” due to their hump-backed appearance—are deceptive creatures for their small size (~ 1/8″ long).  You usually don’t notice them as much by sound like buzzing mosquitoes, but when they land to feed, these tiny flies are vicious.  Rather than using needle-like mouthparts to delicately probe for blood vessel like mosquitoes, black fly mandibles resemble the jagged edge of Rambo’s survival knife which they use in a “slash-and-slurp” approach.  These mouthparts slice into flesh to create a pool of blood which they then consume.  If this sounds unpleasant—it is!  Reactions to black fly bites can sometimes be severe, with fever and enlargement of nearby lymph nodes.  In addition, their sheer numbers can take a psychological toll and can be a strong test of one’s fortitude if you must be outdoors during peak black fly season.

Adult black fly taking a blood meal. Photo Credit: D. Sikes, via Flickr.

Of the 30 species in Wisconsin, only a handful actually bite humans.  Other species are “picky eaters” with a strong preference for other animals.  For example, Simulium annulus, specializes on common loons and in “bad” years the constant pestering can force adult loons to abandon their nests.  Other birds, such as purple martins and bluebirds can face high rates of chick mortality when the black flies are bad.  Pets, like dogs can commonly get bites and large pinkish welts on the soft skin of their belly.  Dairy cows can be harassed to the extent that feeding and weight gain is greatly reduced and milk production all but ceases.  In some cases, large animals including deer, cows, and horses have been killed outright by black flies.

With that said, if you’ve ever encountered an outbreak of black flies, you’d likely remember.  If you haven’t bumped into black flies before, you’re perhaps in a good spot on the map.  The larvae of many black fly species tend to be associated with streams and rivers, meaning that geography can play a role with outbreaks.  Within the state, areas near the Wisconsin River and other large rivers and streams tend to see the most intense black fly activity.  Black flies can be even worse to the north.  These insects can be notoriously bad in the Boundary Waters Canoe Area in June, and in Canada black flies have even been enshrined in film and a surprisingly catchy folk song.

Black fly larvae in a river. Photo credit: GlacierNPS via Flickr

If there’s good news about black flies, it’s that the adults are short-lived.  Wisconsin tends to see a blitz of activity spanning a few weeks in late spring.  When black flies are active, the best approach is to layer up with long sleeves, break out the repellents like DEET, and use a head net if needed.  If you’re in an area with intense black fly activity, cutting back on outdoor activities until these insects run their course for the year may be the simplest option.

What’s Trending? Ticks and Lyme Disease

This month’s post features contributions from Dr. Bieneke Bron


As stories about measles and vaccinations circulate in the news, it’s easy to lose track of other emerging health threats.  May is Lyme Disease Awareness month, and if you want to look at an emerging health threat particularly relevant to the Midwest, look no further than deer ticks and Lyme disease.

Adult female deer tick (Ixodes scapularis). Photo credit: Robert Webster / xpda.com / CC-BY-SA-4.0 via Wikipedia.

A Brief History of Deer Ticks and Lyme Disease:
The Lyme disease story is surprisingly new to Wisconsin and deer ticks are something that our grandparents didn’t have to deal with while growing up.  It wasn’t until the late 1960’s that our first deer ticks were documented in northern Wisconsin. At the time, this particular tick was known from more southern locations, so the first Wisconsin reports were noted as a curiosity in the scientific literature.  In actuality, this marked an early foothold of deer ticks in the region, which have spread rapidly.  Fast forward 50 years and deer ticks are widely distributed around Wisconsin and surrounding states.

Deer ticks are only one component of the Lyme disease equation. The spirochete bacterium Borrelia burgdorferi (or the closely-related B. mayonii) must be transmitted by these ticks to cause Lyme disease in humans.  Similar to the deer tick situation, Lyme disease has had an interesting recent history.  Research from the Yale School of Public Health suggests an ancient origin of Borrelia burgdorferi, but the first clinical cases of Lyme disease weren’t formally documented in the medical literature until the 1970’s.  At that time, an unusual cluster of juvenile arthritis cases with an accompanying rash helped researchers characterize the disease near Lyme, Connecticut*.  It wasn’t until the early 1980’s that the roles of deer ticks and Borrelia burgdorferi were recognized.

Skip ahead a few decades and the numbers for Lyme disease have increased steadily.  Today Lyme disease is the most commonly reported arthropod-borne disease in the US with over 40,000 confirmed and probable cases in 2017 alone.  Looking at Wisconsin’s statewide averages, approximately 20% of deer tick nymphs (juveniles) and 40% of adult deer ticks are carrying Lyme disease, which are alarmingly high percentages.

Deer tick nymphs (juveniles) next to chia seeds, sesame seeds, flax seeds and a penny for size reference. Photo Credit: Dr. Bieneke Bron, MCE-VBD.

Tracking Ticks with Mobile Technology:
With the changing tick and tick-borne disease situation over the last 50 years, understanding the factors that influence where and when ticks are encountered is more important than ever before.  Researchers at the Midwest Center of Excellence for Vector-Borne Disease and the Northeast Regional Center for Excellence in Vector-Borne Diseases have teamed up to develop The Tick App—a mobile app to help gather critical clues to better understand human exposure to ticks.  The app, available in iTunes and GooglePlay, not only allows the public to contribute valuable data to tick researchers, but the app provides helpful tips on tick identification, activity, and precautions to take.  During the tick season, the researchers will also identify ticks from the images submitted in the app.

As we move into peak tick season, Midwesterners should be aware of ticks and take appropriate precautions to protect themselves [Recommended reading: the ABCs of Tick Season].  Learn more about The Tick App by visiting thetickapp.org or follow on Twitter @TickAppOnTour.


*Interestingly, a 57-year old physician from Medford, Wisconsin, was diagnosed with the hallmark rash of Lyme disease (erythema migrans) in 1969 [Scrimenti 1970, Arch Derm].  Just imagine, Lyme disease being known as Medford disease…

…An even earlier account of the Lyme-like “bullseye” rash was described in Europe by Arvid Afzelius in 1909.

2018’s Top Trends from the Diagnostic Lab (Part 2)

In this post, we’re continuing to count down the University of Wisconsin Insect Diagnostic Lab’s top arthropod trends of 2018. This is the second half of a two part series; the first half can be found here.


5) White-Lined and Other Sphinx Moths:
The white-lined sphinx moth (Hyles lineata) can be a common species, so encountering one of the 3 inch long hornworm caterpillars isn’t unusual. However, these caterpillars can also be encountered in massive road-traversing hordes if the conditions are just right. From midsummer onwards, large numbers of these caterpillars were observed around the state—in some cases by the tens of thousands. If you didn’t spot any of the caterpillars themselves, you might have encountered the large adult moths with their hummingbird-like behaviour in late summer. Several other sphinx moths species also had a strong presence in 2018, such as the clearwing hummingbird moths and the tobacco and tomato hornworm caterpillars which can regularly be encountered in gardens as they munch away on tomato and pepper plants.

Large, dark-colored hornworm caterpillar of the white-lined sphinx moth on a plant
Large, dark-colored hornworm caterpillar of the white-lined sphinx moth. Photo submitted by Ted Bay, UW-Extension

4) Sawflies:
Sawflies, the caterpillar copycats of the insect world, are a diverse group, so they’re always present to some extent. Last year saw an unexpected abundance of two particular types in Wisconsin—the dogwood sawfly and the non-native Monostegia abdominalis, which feeds on creeping Jenny and related plants from the loosestrife group (Lysimachia species). While sawflies are plant feeders, dogwood sawflies can also damage the soft wood of a home’s siding or trim when these insects excavate small chambers to pupate in. The UW Insect Diagnostic Lab saw a distinct bump in reports of wood damage from the dogwood sawfly last year.

Whitish larva of the dogwood sawfly curled up on a dogwood leaf
Larva of a dogwood sawfly showing the whitish, waxy coating. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

3) Armyworms:
True armyworms (Mythimna unipuncta) can be a dynamic and sporadic pest in the Midwest. This species doesn’t survive the cold winters of our area, so adult armyworm moths must invade from the south each spring. Depending on national weather patterns, the arrival of the adult moths can vary significantly from year to year. If an early mass arrival is followed by abundant food and ideal conditions for the ensuing caterpillars, large populations can result. Once they’ve arrived, true armyworms can go through 2-3 generations in the state and this second generation of caterpillars made an alarming appearance in mid-to-late July. Under the conditions last summer, massive hordes of these caterpillars decimated crop fields before marching across roads by the tens or hundreds of thousands to look for their next meal. In some cases, that next meal included turfgrass, meaning that some Wisconsinites came home from work to biblical hordes of caterpillars and half-eaten lawns in late July.

Striped caterpillar of the true armyworm
Caterpillar of the True Armyworm (Mythimna unipuncta). Photo Credit: Lyssa Seefeldt, University of Wisconsin-Madison Extension

2) Monarch Butterflies:
Much to the delight of fans and conservationists, the iconic monarch butterfly (Danaus plexippus) appeared to have a banner year in the Midwest in 2018. Reports and observations of high numbers of monarchs poured into the Insect Diagnostic Lab during the summer months. As comforting as these reports were, the butterflies still faced a perilous 2,000 mile journey to reach their overwintering grounds in Mexico.  The most consistent measurement of the eastern monarch population comes from estimating the area occupied by the densely-packed overwintering butterflies.  In late January the latest count was released with encouraging news—the eastern monarch population is up 144% over last year and is estimated to be the largest in over a decade.  In contrast, the western monarch population overwinters in southern California and has recently dipped to alarmingly low numbers. Regardless of the winter assessments, monarchs face tough challenges and Wisconsinites are encouraged to help conserve this iconic species.  The Wisconsin Monarch Collaborative recently launched a website with resources for those wishing to join the effort.

Seven monarch butterflies nectaring on a flower
Multiple monarch butterflies nectaring on a single plant in August. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

1) Floodwater Mosquitoes:
Mosquitoes snagged the top spot on 2018’s list for good reason. The upper Great Lakes region is home to over 60 different mosquito species, but one subset—the “floodwater” mosquitoes—drove the storyline last year and impacted outdoor activities through much of the spring and summer months. Mosquitoes in this group, such as the inland floodwater mosquito (Aedes vexans), flourish when heavy rains come. Last year’s mosquito season kicked off in force with a batch of pesky and persistent floodwater mosquitoes just before Memorial Day weekend. Mosquito monitoring traps in southern Wisconsin captured record numbers of mosquitoes shortly thereafter. Later in the year, the Midwest experienced an unprecedented series of severe rainstorms, setting the stage for an encore performance of these mosquitoes. It was this second explosion of mosquitoes that caught the attention of anyone trying to enjoy the outdoors in late summer—a time of the year when mosquitoes are typically winding down in the state.

Ephemeral pools of water created ideal conditions for floodwater mosquitoes in late summer. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

September’s Mosquito “Madness”

While much of our insect activity in the Midwest slows down as summer draws to a close, some areas have seen an unusual increase in mosquito activity recently.  In Wisconsin, we generally expect mosquitoes to be “bad” from late spring through the summer months, but these pesky sanguivores typically fade away as autumn approaches.  September of 2018 has definitely bucked the trend, and mosquito pressure has been very high in many parts of the state and region this month.

As with other mosquito stories, the common denominator is water—in this case, the unprecedented rainfall events in late August and early September.  During this time, a series of storms dropped heavy rains across large swaths of Wisconsin and surrounding states.  Much of Wisconsin received several inches of rain, and some southern counties were bombarded with 10+ inches of rain in short periods of time.  Devastating flooding ensued, and it was only a matter of time before the mosquitoes responded as well.

Flooding caused over $200 million in damages in Wisconsin alone and set the stage for September’s unseasonably high numbers of floodwater mosquitoes. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

Surprisingly, not all mosquitoes can take advantage of floodwaters and some species have a strong preference for more permanent bodies of water, such as tree-holes, man-made objects, marshes, and other areas that can hold water for weeks or months on end.  Out of the 60+ mosquito species in the Midwest, it’s a much smaller subset that has flourished lately—a group appropriately called the “floodwater mosquitoes” for their ability to use temporary water sources to their advantage.  Members of this group, including the currently-abundant “inland floodwater mosquito” (Aedes vexans), tend to lay eggs in low-lying areas without water.  Laying eggs away from water may seem like a counterintuitive strategy, but the hardy eggs simply bide their time until heavy rains arrive—in some cases, years later.

Relying upon temporary resources can be a risky strategy; if the waters dissipate too quickly,  stranded larvae or pupae can be doomed.  Floodwater mosquitoes have evolved to race against the clock, with eggs that hatch shortly after exposure to water, followed by hasty growth and development.  Under the right conditions, it can take less than a week for these mosquitoes to make it to the adult stage.  This scenario is exactly what played out in our area—the rains came, followed shortly thereafter by hungry adult mosquitoes.

The “inland floodwater mosquito” (Aedes vexans) is currently abundant in the Midwest. Photo Credit: Sean McCann, via Flickr

With the unseasonably high mosquito pressure this September, one of the commonest questions has been, “when will it stop?!”  While the mosquitoes have undeniably been bad lately, we’re past the worst of the situation.  Mosquitoes and other insects are “cold-blooded” creatures, so there’s a general relationship between warmer temperatures and insect activity. Most of our insects in the Midwest become lethargic when temperatures dip into the 50s; below 50˚F mosquitoes are often too lethargic to fly, let alone pursue a blood meal.  We saw unusually high mosquito activity in early- and mid-September when temperatures remained in the 70s and 80s most days.  Looking at the weather for the near future, many parts of Wisconsin are expecting more seasonal temperatures, which will provide relief.  Mosquitoes might still be encountered on warm fall days, but evening temperatures may simply be too chilly for mosquitoes to go about their business and impending frosts will be the final “nail in the coffin” for September’s floodwater mosquitoes.

In the meantime, the best way to deal with the late season mosquitoes may be to embrace “flannel season” and put on some long-sleeved layers as a physical barrier to bites, and use  EPA-approved repellents as needed (such as on warm days).  Avoiding prime mosquito feeding times (dawn/dusk) and good mosquito habitat can help you avoid bites as well.  It may be sad to see summer go, but the changing leaves and cooler temperatures also signal the winding down of mosquito activity for the upper Midwest.

To Boldly Go Where Man Has Gone Before: Pests on the Move

Since the earliest days of mankind, we’ve excelled at exploring and expanding our presence to nearly every spot on the map With all our wanderlust, we’ve been equally adept at taking other species with us as we go—often with unintended consequences. 

In some situations, species have been deliberately moved by humans: livestock to the new world, the introduction of birds from Shakespeare’s plays into Central Park,  and even the notorious gypsy moth was transported from Europe in a failed attempt at an American silkmoth industry On top of that, there’s an extraordinarily long list of species that have been accidentally moved, with significant impacts Stowaway rats on the ships of European explorers and traders would be one of the most notorious examples Rats introduced to new island environments wreak havoc on native birds and reptiles by devouring vulnerable eggs Insects have also been transported around the globe with devastating results and some of North America’s most important and emerging insect pests originate elsewhere on the planet: Japanese beetle, emerald ash borer, brown marmorated stink bug, and the spotted lanternfly.

Aedes sp. mosquitoes preparing for a blood meal.  Photo Credit: Ary Farajollahi, Bugwood.org.

One of the insects best adapted to follow humans is the notorious mosquito Certain mosquito species (peridomestic species) possess traits that allow them to take advantage of conditions in areas disturbed by humans and thrive in those spots.  With humans came environmental modification, construction, and discarded trash of one kind or another.  Some mosquitoes might have originally relied on the water pooled in natural containers, such as rotted out tree stumps to reproduce, but can just as easily take advantage of water-filled containers, ditches, and other artificial habitats.

In modern times, automotive tires have become a key habitat for certain mosquito species Tires not only are perfect objects for holding water for extended periods, but they also provide the dark, sheltered habitat favored by some female mosquitoes looking to lay eggs Tires are an important way for mosquitoes, like the Asian Tiger Mosquito (Aedes albopictus) to be moved into and around the US (including the Midwest) Other species, like the Asian Rock Pool Mosquito (Ochlerotatus japonicus), are also easily transported in human materials.

Hyacinth flower sold from a local store, including a vase pre-filled with water. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

A recent case at the UW Insect Diagnostic Lab illustrates the ease with which non-native mosquitoes can be moved around the country In the first part of 2018, stores have been selling hyacinth bulbs in vases pre-filled with water as a way to force the bulbs to bloom into a flash of color during the dreary winter months In a recent discovery in southeastern Wisconsin, a vase purchased at a local store ended up yielding half a dozen larvae of the non-native Asian rock pool mosquito.  The exact origin of the mosquitoes isn’t known at this time.

A bonus surprise with the flowers—larvae of the Asian rock pool mosquito (Ochlerotatus japonicus). Animation credit: PJ Liesch, UW Insect Diagnostic Lab.

These mosquitoes won’t be much of a concern in the grand scheme of things as Ochlerotatus japonicus has been present in Wisconsin for over a decade and is already established hereHowever, such cases do leave open the possibility of non-native mosquitoes being moved into parts of the country where these pests have not been encountered beforeWhere humans go, pests will boldly follow.

Under the Microscope: Arthropod Trends of 2017

Over 2,500 cases flowed through the doors of the UW Insect Diagnostic Lab last year, ranging from the typical June beetles through bizarre creatures that most humans will never see in their entire lives (like the itch-inducing pyemotes grain mite).  Perhaps Forrest Gump said it best when he quipped, “life was like a box of chocolates—you never know what you’re gonna get.”  A distinction amongst insects, however, is that the “box” contains 20,000+ possibilities in Wisconsin alone and over well 1,000,000 globally.  With that said, a year at the UW Insect Diagnostic Lab is like having one humongous, box of really awesome chocolates, without all the calories.

Finding a pyemotes itch mite is like trying to find a needle in a haystack, except in this case these microscopic mites were in a farmer’s batch of corn. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

With insects and related creatures, the weather can of course have a big impact and there definitely were examples of this in 2017.  The current cold winter aside, the last two winters had been otherwise mild, giving a few insects suited for warmer conditions a chance to inch their way northward.  Last spring and summer, this meant a bunch of sightings of an otherwise uncommon bee for our area known as the carpenter bee due to its habit of tunneling into unpainted cedar trim and other wood.  In a typical year, I might see a few cases out of the southeastern corner of Wisconsin, but 2017 had regular reports of these bumble bee look-alikes during the spring and summer months.  Similarly, praying mantids often meet their maker at the hands of a cold winter, but were surprisingly abundant in late summer and fall of last year.  Ticks were also extremely abundant last spring and with the rainy start to the summer, mosquito numbers were at an all-time high in some traps.  Mosquitoes were also a big deal in the news, with Wisconsin’s first confirmed reports of the Asian Tiger Mosquito last July.

Asian Tiger Mosquito (Aedes albopictus). Photo credit: James Gathany, Centers for Disease Control

The creature that amassed the most phone calls and emails in 2017 was the notorious Japanese beetle, which likely also benefited from the warmer than average winters these past few years.  For Wisconsin gardeners and farmers, the Japanese beetle is certainly a formidable foe, but at least there are ways to mitigate the damage.  In contrast, there’s another destructive pest wiggling its way into the spotlight in the state, which is much more difficult to control—an invasive earthworm commonly known as the jumping worm.  While they may not be insects, these earthworms are creepy-crawly and can wreak havoc in  gardens and flower beds, so I received a fair number of reports and questions.  What stood out to me in last year was the rapidity with which these destructive worms have been moved around the state (moved—as in humans have moved soil, plants, mulch, and similar materials).  Jumping worms were first found in the state in 2013 (in Madison), but have now been spotted in roughly half of the counties in Wisconsin.  To make matters worse, we don’t have any highly effective tactics to prevent these worms from turning rich garden soil into the consistency of dry, crusted coffee grounds—gardeners beware!

Speaking of invasive species, the emerald ash borer has continued its march through the state and now has footholds in some of our northern counties including Chippewa, Douglas, Eau Claire, Marathon, Marinette, Oneida, and Sawyer counties.  Unfortunately, our greatest concentrations of ash trees are in the northern part of the state (e.g. black ash in swampy areas), and the loss of ash from northern wetland areas could result in significant ecosystem effects.  Other recent invaders like the spotted wing drosophila and the brown marmorated stink bug had busy years as well.

Rusty patched bumble bee (Bombus affinis) visiting a flower in Middleton, WI. Photo credit: Rick Terrien

In other insect news, it seemed to be a good year for monarch butterflies in 2017, and the rusty-patched bumble bee finally made it onto the federal endangered species list. I was pleasantly surprised by a number of confirmed sightings of the rusty-patched bumble bee in the state as well. Perhaps my favorite “bug” story for the year involved black widow spiders.  It’s not common knowledge, but we do technically have a native black widow species in the state (Northern Black Widow, Latrodectus variolus).  It’s a reclusive species and is rarely encountered in Wisconsin, but reports trickled in once or twice a week at some points during the summer months (details to follow in a future blog post).

With so many cases last year, we’re really only touching the tips of the antennae.  If you’re interested in hearing more of the unusual stories from the UW Insect Diagnostic Lab, I’ll be giving a “highlight” talk on May 4th on the UW campus.