With the media craze about “murder hornets” this past spring, I’ve seen a definite increase in reports of Asian giant hornet look-alikes at the UW Insect Diagnostic Lab this summer. Many folks recognize the commonest look-alike in the Midwest, the eastern cicada killer (Sphecius speciosus), which becomes active in July around the time that their prey (cicadas) start emerging. Another look-alike is one that you might not have bumped into before—the great golden digger wasp (Sphex ichneumoneus). Similar to Asian giant hornets, great golden digger wasps are large and nest in the ground, which are reasons why they may be mistaken for the former.
If you haven’t spotted one before, great golden digger wasps can be a bit intimidating in appearance as they can easily be over an inch long. However, their anatomy and appearance are quite different compared to Asian giant hornets. Great golden digger wasps are mostly black with a rusty-reddish color at the base of the gaster (“abdomen”). Their legs are the same reddish color and the black thorax and head possess fine golden setae or “hairs” (hence “golden” in their name). In contrast, Asian giant hornets have distinctive black and yellow stripes on their gaster and a vibrant yellowish-orange head. Great golden digger wasps belong to the “thread-waisted” wasp family (Family Sphecidae) and have a long, slender petiole (“waist”). This isn’t as thin and narrow as the “waist” of the related black and yellow mud dauber (Sceliphron caementarium), but still is quite noticeable when viewed from the side.
In terms of their biology, both Asian giant hornets and great golden digger wasps do nest in the ground, but the similarities end there. The Asian giant hornet is really quite similar to our ground-nesting yellowjackets in terms of their nesting behavior. These are social creatures which start nests from scratch in spring and build up in size over the course of the warmer months. Colonies ultimately die out in fall except for the “new” queens which overwinter. With a large colony of relatives to defend, social wasps can be defensive, especially when colonies are at peak size.
In contrast, great golden digger wasps are solitary ground nesters. Without a large colony of relatives to defend, they’re usually non-aggressive and very unlikely to sting. Stings are only likely if one were to pick one up bare-handed—in which case you might be asking for it! Similar to cicada killer wasps, each female great golden digger wasps excavates small tunnels in sandy soil and provisions them with prey for their young to feed on. In the case of the great golden digger wasp, prey consists of katydids, crickets, and relatives from the “grasshopper” group (Order Orthoptera). Rather than kill outright, the females inject their prey with a paralytic “cocktail” to keep them alive and fresh for their young to feed on—what a way to go! In addition to hunting katydids, adult great golden digger wasps visit flowers and can be beneficial pollinators.
Because they’re unlikely to sting humans, controlling great golden digger wasps is rarely justified and these magnificent creatures can simply be admired. Ultimately, these wasps are strongly associated with sandy soil, so if you see them in your yard every year and would prefer to not have them around, modifying the landscaping may be a long-term option to dissuade them from an area.
Author’s note: As of August 2020, Asian giant hornets have not been found in Wisconsin or anywhere in the Midwest. In North America, these insects are only known from far northwestern Washington state and nearby parts of British Columbia.
See this earlier post for additional details on the Asian giant hornet.
Perhaps you’ve heard some buzz about periodical cicadas (Magicicada spp.) lately. These insects resemble our typical “dog day” cicadas, which we see in mid-to-late summer in Wisconsin, but they are orange and black with vibrant reddish eyes instead of a dull greenish color. Parts of the US are currently seeing mass emergences of periodical cicadas, which appear by the millions every 13 or 17 years depending on the species. I’ve had a number of questions this last month asking if this was “the year” for us to see them in Wisconsin, but it’s not time for the big show…yet.
Periodical cicadas are sorted into cohorts known as “broods”, which occur in particular geographic areas and emerge at specific points in time. For the most part, these insects are excellent timekeepers and some broods have been documented as far back as the 1600’s in the eastern US. There are entire websites and apps dedicated to these insects and their schedules, and scientists have labelled broods with Roman numerals to help differentiate the cohorts.
With all the broods out there, some parts of the US do see these cohorts overlap in space, but these can be separated by the years in which they emerge. In Wisconsin, the situation is fairly straightforward as we only see a single brood: Brood XIII. Brood XIII’s 17-year cicadas last emerged in 2007, meaning that we’ve got four more years to wait until their mass emergence in 2024.
Interestingly, I’ve received a number of photos and reports of periodical cicadas in Wisconsin over the last month or so. I’ve had several confirmed reports from the Lake Geneva area (Walworth County) a confirmed report from southeastern Dane County, and a suspected report from Sauk County. While most periodical cicadas stick to the schedule, occasionally some of these insects veer off course. These out-of-sync individuals are referred to as “stragglers” and it turns out that Brood XIII has a history of these stragglers. In the late 1960’s, large numbers of stragglers were documented in the Chicago area. Likewise, many of the Chicago suburbs are seeing a similar phenomenon this year. With that said, we did technically see some periodical cicadas this year, but we’ll have to wait a few more years before the real “fireworks”.
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.
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 Times. Despite 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.
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
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.
Since early 2020, COVID-19 has changed the ways that Americans go about their everyday lives. Here in Madison, WI, the University of Wisconsin-Madison has taken a number of steps in response to the COVID-19 situation such as switching to online classes and having most employees work remotely. The full details of UW-Madison’s response can be found here: covid19.wisc.edu.
Despite the disruptions, part of the Wisconsin Idea is that the activities of institutions like UW-Madison should provide benefits to residents in all reaches of the state. To that end, the UW Insect Diagnostic Lab remains open to provide insect/arthropod identification and outreach services to residents of Wisconsin, with some notable changes. Bookmark this page for updates which will be posted as they arise.
General Diagnostics & Questions:
Many of the services of the IDL, such as email photo submissions, remain unchanged. Important points are noted below:
Arthropod ID requests (insects, spiders, etc.) can still be submitted to the UW Insect Diagnostic Lab
Digital photographs are the best way to submit an ID request in the time of COVID-19. See this webpage for required information and tips on submitting insect images.
Visitors are not allowed in the diagnostic lab at this time.
Physical samplesUpdate (11/1/20): For the remainder of 2020, youmust contact me before sending in a physical sample. Processing times will be significantly longer than usual.Please see this webpage for instructions on how to submit physical samples by mail.
General insect questions can still be submitted by email to firstname.lastname@example.org (best option) or by phone. I will continue to have regular email access while working remotely, but phone responses will likely be delayed. Email will be the best way to reach me for the time being.
The UW Insect Diagnostic Lab regularly provides outreach around Wisconsin via public radio, workshops, public seminars, and other venues. Unfortunately, the COVID-19 situation is impacting in-person delivery of this outreach. See below for additional details:
In-person presentations provided by the UW Insect Diagnostic Lab have been cancelled until further notice.
If interested in distance education (via Zoom, Skype, Google Hangouts, etc.), feel free to reach out to me by email (email@example.com).
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.
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.
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.
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.
Elongate hemlock scale attacks over 40 species of conifers—especially hemlocks which can be common throughout the Appalachian Mountains, and Fraser firs and balsam firs, which are commonly grown as Christmas trees. Certain types of spruces and pines can also be attacked. Established populations of elongate hemlock scale are not known from Wisconsin, but a recent detection of this pest in the state raises concerns for Christmas tree growers, the plant nursery industry, tree care professionals, and homeowners with conifer trees in their yards. Forested areas are also at risk, meaning the stakes are potentially high with this insect.
While insect activity is quiet in the Midwest this time of the year, we’re hearing about the elongate hemlock scale now due to its Christmas connection. Similar to 2018, the Wisconsin Department of Agriculture, Trade and Consumer Protection recently found that fir Christmas trees, wreaths, and other holiday decorations infested with EHS had been shipped to Wisconsin from North Carolina. The picturesque Blue Ridge Mountains of western North Carolina provide ideal habitat for Fraser firs—one of the most popular species of Christmas trees. North Carolina grows approximately a quarter of all the Christmas trees sold in the US each year and with elongate hemlock scale established in that state, it increases the risk of movement of this invasive insect around the country.
Elongate hemlock scales look unusual as far as insects go. These insects have traded mobility for defense—they hunker down on plants and produce a waxy coating which helps protect them from predators and parasites. As a result, elongate hemlock scales aren’t easily recognizable as insects since the usual signs of segmentation—body regions, legs, antennae—are not readily visible. Instead, these insects have a vague, oblong appearance. Adult females are small (just under 1/10th of an inch long) and are covered with a waxy brownish coating. They are typically found on the undersides of needles. Males are slightly smaller and develop beneath pale whitish coverings. Mature males do emerge with wings but are weak fliers and travel short distances to mate with the wingless, immobile females.
Under their protective coatings, these insects use needle-like mouthparts to suck fluids from plants. With their small size, damage occurs when large numbers of individuals infest plants. Their waxy coverings also limit the effectiveness of insecticides, making EHS a challenging pest to control if they become established.
Because elongate hemlock scale has been detected in Wisconsin this year in Christmas trees and other holiday decorations, a key objective at this point is to prevent this insect from getting a foothold in the state. By all means, continue to enjoy your holiday decorations, but when you’re ready to remove these materials, take the following steps to help prevent this insect from becoming established in Wisconsin:
1) If your Christmas tree or natural wreaths, garlands, or other decorations are from a local Christmas tree farm or elsewhere in Wisconsin, no special precautions are needed for elongate hemlock scale. Because EHS is not established in the state, these materials can be removed as usual at the end of the holiday season.
2) If your Christmas tree or natural wreaths, garlands, or other decorations are from a big box store, grocery store, or similar vendor, or if you are not sure of the origins of these materials, it is advised to check these materials for signs of elongate hemlock scale (i.e., brown spots on the undersides of needles). The Wisconsin Department of Agriculture, Trade, and Consumer Protection is advising that infested or suspect materials preferably be burned (check with the DNR for any burning restrictions in your area). Alternatively, such materials could be bagged and discarded as waste. Infested or suspect materials should not be composted or used for wildlife habitat in your yard.
For additional information on elongate hemlock scale, visit the WI-DATCP EHS page and the recent press release about the 2019 EHS detection.
“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 cruzi—a 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 (Triatomasanguisuga)—ranges from Latin America as far north as southern Illinois.
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.
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.
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:
Masked hunter bugs are entirely dark while eastern conenose kissing bugs have red on their body
Masked hunter bugs lack the projecting “conenose” present on the head of kissing bugs
Masked hunter bugs have a bulging, “muscular” appearance of their prothorax (trapezoidal region behind the head) when viewed under magnification
Masked hunter bugs have stout beak-like mouthparts while kissing bugs have long, slender mouthparts when viewed under magnification
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/
It’s a funny world we live in. We hear regular reports of insect declines in the news and still get bombarded with constant ads for services pitching a mosquito free yard all summer and a grub free lawn. But what about simply appreciating insects and the critical roles they play in our everyday lives?
That’s a goal of the first ever Wisconsin Insect Fest being held at the Kemp Natural Resources Station in Woodruff, Wisconsin later this month. The two-day event—being held on Friday, July 26th and Saturday, July 27th—is a celebration of insects.
Wisconsin Insect Fest is free, open to the public, and will feature a wide range of activities for insect enthusiasts of all ages. Topics will range from how to observe and collect insects, to the role of insects in the ecosystem, entomophagy, and even forensic entomology. The Wisconsin Insect Fest will also feature The Great Wisconsin Bug Hunt—a 24-hour BioBlitz activity to see just how many arthropods can be spotted at the Kemp station in a 24-hour period (including a night time activity in conjunction with National Moth Week).
If you love insects, join in the festivities at the Wisconsin Insect Fest later this month or check out the event website for details: tinyurl.com/WisconsinInsectFest
With daylight saving time beginning over the weekend and warmer temperatures knocking at our door, spring is finally crawling our way. Last winter is one we won’t soon forget—the season started out mild before temperatures plummeted with January’s polar vortex. During the coldest stretch, our coping strategy might have involved layers of blankets and reruns on Netflix, but what about the bugs? Questions regarding the winter impacts on insects have been some of the commonest at the UW Insect Diagnostic Lab this year. There will undoubtedly be some impacts of this year’s polar vortex, although many insect species are well-equipped to deal with the cold. Before we know it, overwintering insects will become active again in the Midwest and many species will simply shrug off the polar vortex as if it hadn’t happened. For insects that didn’t fare as well in the cold, high reproductive capacities will likely allow their numbers to bounce back relatively quickly.
Thus, 2019 isn’t going to be insect-free by any means and intuitively this makes sense. We know that every year insects make it through the winter months and become active as temperatures creep up in spring. Looking at an evolutionary time scale, this year’s cold snap wasn’t the first time that the species in our area have encountered frigid temperatures before, and many creatures are adapted to survive surprisingly cold conditions. We might have chosen to block it out of memory, but the Midwest experienced a very similar situation a mere five years ago. Weather patterns in January of 2014 saw temperatures dip to -20˚F and colder in some spots of the Midwest. The following summer, we still had plenty of insect activity in the region.
Since we don’t see insects bundling up with tiny mittens and scarves, how do they make it through the winter? It turns out that insects and other arthropods have a number of strategies to help them survive. For starters, insects typically have a particular life stage (e.g., egg or pupa) that is more tolerant of adverse environmental conditions, such as freezing or desiccation. Passing through the winter as a more resilient life stage is a good starting point.
Some of the other strategies are surprisingly similar to humans. Just like snowbirds heading to warmer states for the winter, certain insects like monarch butterflies and green darner dragonflies migrate southward to avoid the coldest temperatures. Our official state insect (the honey bee) doesn’t migrate, and instead chooses to remain active. Honey bee colonies shiver together as an insect version of central heating to keep the inside of their hive a constant temperature. Other insects simply seek shelter and overwinter in protected locations to avoid the worst of the cold. Insects like the multicolored Asian lady beetle, boxelder bugs, and the invasive brown marmorated stink bug are fond of sneaking into man-made structures to spend the winter. If insulation and central heating make homes warm enough for us, it’s plenty warm to prevent insects from freezing. In more natural settings, such insects might end up sheltering in rock piles or beneath the loose bark of a dead tree. Those locations might not be as toasty as a house, but they can still provide adequate respite from the cold—meaning that insects using this strategy should have been well protected from this year’s cold spell. Similarly, many insects and other arthropods spend the winter below ground or on the surface of the ground amongst a layer of insulating leaf litter. In addition, many parts of Wisconsin had a solid covering of snow by the time the polar vortex arrived, so creatures such as ticks had a thick layer of insulation from the coldest of the cold.
Another strategy utilized by insects is the production of natural antifreeze compounds (specific alcohols or proteins) which serve as cryoprotectants to help prevent freezing within their bodies. We know that a cup of water will turn to ice at 32˚F, but dissolve salts or other substances in that same water and it will require colder temperatures to freeze it. Insects producing high concentrations of these cryoprotectants can remains unfrozen at surprisingly low temperatures, similar to a bottle of high-proof spirits kept in a freezer. Taking it even further, the common black and brown woolly bear caterpillars seem to embrace the cold and actually allow ice to gradually form within their bodies. This may sound like a fatal mistake, but by regulating the formation of ice crystals on their own terms, woolly bear caterpillars are able to control where ice formation occurs and limit it to specific areas of their bodies to prevent damage. If the same caterpillars were unprepared and froze rapidly, their cells might burst like a can of soda put into a freezer.
And then the ash borer…
The insect I’ve gotten the most questions about lately has been the emerald ash borer. While not native to our area, this invasive pest comes from similar latitudes of eastern Asia and the cold-hardy larvae are fortified with cryoprotectants as they spend the winter beneath the bark of ash trees. These natural antifreeze compounds have their limitations though, and just like sidewalk salt failing to melt ice on a really cold day, the cryoprotectants only work down to certain temperatures before freezing (and death) occurs. For emerald ash borer, the point at which freezing spontaneously begins to occur (the supercooling point) is when temperatures dip into the range of -13˚F to -23˚F. This year’s polar vortex did see temperatures fall into and below that range, which would have killed plenty of emerald ash borer larvae, although the insulating effects of the tree bark likely provided some buffering.
Emerald ash borer populations will almost certainly take a hit from this year’s polar vortex, but it’s not going to be a knockout blow. Give it some time and the reproductive capacity of this invasive species will allow populations to rebound. The news reports of cold-induced EAB mortality in early February might have been encouraging, but scientific models from the US Forest Service suggest that to really knock down EAB in the long run, we’d have to experience arctic blasts on a regular basis—news that many Midwesterners aren’t likely to receive warmly.
Further Reading: For a great read on how wildlife survive the winter, check out Bernd Heinrich’s Winter World
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.
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.
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!
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.