Tag Archives: Featured

Do mosquito yard sprays harm other insects?

If you’ve noticed all the lawn signs for mosquito treatments, you may be wondering if mosquito yard sprays harm other insects. If so, you’re not alone.  As an Extension entomologist, this is a common question that I get from the public every year.  To get to the bottom of this question, it helps to understand the different types of mosquito spraying that’s done.

One approach (Ultra Low Volume or ULV) is sometimes used by municipalities or abatement districts to control mosquitoes.  These ULV applications generally involve using specialized equipment mounted on trucks or aircraft to apply extremely tiny droplets which kill adult mosquitoes by direct contact as the droplets float in the air.  Such applications use very small volumes of insecticides either undiluted or with minimal dilution and are often applied after dark when mosquitoes are most active.  The microscopic droplets from ULV treatments disperse relatively quickly and have little residual activity—think of them like a “one time strike” to knock down mosquito numbers.

The vast majority of research on mosquito sprays and non-target organisms has looked at these ULV-type treatments.  Some good news is that these studies suggest that impacts to non-target insects are relatively small and short-lived.  It turns out that the ULV treatments are most effective on insects with very small body mass, so insects larger than mosquitoes tend to be spared.  A good summary of the impacts of ULV treatments on non-target organisms can be found in a 2012 review paper by J.A.S. Bonds in Medical and Veterinary Entomology. 

Many mosquitoes like to rest on vegetation during the day, so some mosquito sprays specifically target these resting sites. Photo credit: Public Domain Image.

Case closed, right?—Not quite. Here in Wisconsin, we don’t really use ULV treatments a whole lot for mosquitoes.  The common yard treatments are what we’d call “perimeter”, “barrier”, or “residual” treatments.  Such treatments are applied via a backpack sprayer to create a coating or “barrier” on treated surfaces which affects mosquitoes that land on it.  These treatments involve applying a residual insecticide (usually from the pyrethroid group) to vegetation in yards and around structures.  The pyrethroid products are broad-spectrum and often last for a few weeks or longer depending on the formulation.  These same ingredients (and sometimes the exact same products) can also be used to control a wide range of yard, garden, and structural pests (e.g., Japanese beetles, garden pests, household ants, etc.).

While the pyrethroids are very common and widely used for a range of purposes, there’s a knowledge gap when it comes to the impacts of mosquito “barrier” treatments on other insects.  While this knowledge gap exists, a few studies raise concerns.  One study by Dr. Karen Oberhauser and colleagues found that monarch caterpillars could be harmed or killed even 3 weeks after spraying.  A more recent (2022) study by Qualls et al. found that honey bees were harmed 28 days after “barrier” treatments were applied.  Thus, if a yard is being sprayed for mosquitoes monthly during the warm season, there are reasons for concern.  More research is needed to help understand the effects of these “barrier” yard treatments on insects that often land on vegetation in yards, such as moths, butterflies, fireflies and other beetles, true flies, bees, wasps and other pollinators.  

Fireflies can be very common on vegetation in a yard during the summer months. Scientists view pesticides as a concern for fireflies globally. Photo credit: RachelEllen via FLickr CC.   

References:

  • Bonds, J.A.S. 2012. Ultra-low-volume space sprays in mosquito control: a critical review. Medical and Veterinary Entomology. 26: 121-130. 
  • Oberhauser, K.S., Brinda, S.J., Weaver, S., Moon, R.D., Manweiler, S.A., and N. Read. 2006. Growth and Survival of Monarch Butterflies (Lepidoptera: Danaidae) After Exposure to Permethrin Barrier Treatments. Environ. Entomol. 35(6): 1626-1634.
  • Qualls, W.A., Moser, B.A., Periera, R.M., Xue, R-D, and P.G. Koehler. 2022. Impacts Of Barrier Insecticide Mixtures On Mosquito, Aedes Aegypti And Non-Target Honey Bee, Apis Mellifera.  Journal of the Florida Mosquito Control Association 69: 34-42.

 

 

Spongy Moth: 2022 Late-Season Update

Heading into the growing season, spongy moth (Lymantria dispar, formerly known as the “gypsy moth”) was poised to have a big year in Wisconsin.  That prediction has held up and I’ve seen an influx of reports of spongy moth caterpillars and damage at the UW Insect Diagnostic Lab (IDL) this spring.  In some areas, these caterpillars are causing conspicuous damage, which has also led to a flurry of questions from the public on what to do about them.  Let’s take a look at how this season has shaped up, how the next few weeks could turn out, and what can be done.

What’s happened so far (as of mid-June)?

After a cool start to spring, we saw some unseasonably warm temperatures during the second week of May, which jump-started a lot of insect activity.  I saw a distinct increase in diagnostic requests at the IDL around this time as well as my first reports of spongy moth caterpillars. 

Daily temperatures for Madison, WI in earyl/mid May, 2022
Unseasonably warm temperatures (90+˚F) for Madison, WI in early/mid May kicked off a lot of insect activity. Source: Weather Underground.

Initial sightings of small caterpillars mostly involved larvae dangling from trees and structures from silken threads—a dispersal mechanism down as “ballooning”.  In other cases, thousands of tiny, dark caterpillars stood out against light-colored siding of homes.  At first, these tiny caterpillars couldn’t cause much damage—with their small size, they simply don’t eat much.  It isn’t until caterpillars are larger and more mature that they really start to chow down and damage increases dramatically. It’s estimated that 80-90% of the damage caused by these caterpillars is from the final two larval substages (instars). Reports of notable damage started to pop up a few weeks later in early June.

Small spongy moth caterpillars. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

Based on the reports coming in to the UW Insect Diagnostic Lab, the heaviest spongy moth activity in 2022 spans from southeastern Wisconsin (Lake Geneva area) west through Rock, Green, and Dane Counties, and north to Sauk, Juneau and Monroe Counties.  Overall, Dane and Walworth Counties stand out for the number of spongy moth sightings and reports of damage that I’ve received.    

What will the next few weeks be like?

The end of caterpillar activity is in sight—but we’re not there yet.  I’m still getting reports of spongy moth caterpillars and likely will for a few more weeks.  In many cases, the caterpillars being spotted are now pretty large (1¾  – 2 inches), meaning that they’re feeding voraciously and causing lots of damage to plants. If there’s a silver lining, it’s that these large caterpillars should also be pupating in the near future—putting an end to their damage for the season. However, I’ve been receiving reports of mixed caterpillar sizes, with some caterpillars only measuring ¾ – 1 inch long.  These smaller “stragglers” will continue to feed and cause damage into July, meaning we’re not entirely out of the woods yet.

A large spongy moth caterpillar showing the distinctive color pattern (click for larger view). The larger, more mature caterpillars cause the bulk of the feeding damage. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

Another variable that could be at play this year is a beneficial fungus known as Entomophaga maimaiga.  This disease can specifically infect and kill spongy moth caterpillars and can play an important role in regulating their populations over time.  Last year’s drought likely helped set the stage for 2022 by suppressing this beneficial fungus.  This spring we’ve had pretty regular precipitation in many parts of the Midwest, which could help put a dent in spongy moth populations if this pathogen kicks in.

What can be done about spongy moth?

This has been one of the commonest questions I’ve been getting recently and have seen plenty of posts on social media sites like Facebook and Nextdoor asking this same question.  Management of spongy moth really depends on the life stage of the insect.  The UW-Madison Division of Extension Spongy Moth website has an excellent month-by-month discussion of management approaches.   

For small numbers of yard trees, the burlap band method can be a way to remove larger caterpillars from the equation.  However, it’s important to understand that this method can be time and labor intensive as you need to check bands daily and brush caterpillars into a container of soapy water to maximize effectiveness. [Note: don’t touch the caterpillars bare-handed, it hurts!].  For large trees, there’s not much else that an individual homeowner can do other than discussing chemical treatment options with an arborist. Many of the online posts I’ve seen have had an element of panic, but it’s also important to keep in mind that trees that are in otherwise good health can generally tolerate defoliation and will push out another batch of leaves later this year.  I start to worry more about plant health when trees are defoliated repeatedly, as that can lead to secondary issues over time.  

Burlap band around an oak tree. Large spongy moth caterpillars feed mostly at night, so burlap bands offer a convenient daytime hiding spot.  Caterpillars can then be brushed into a container of soapy water. Photo credit: Bill McNee, WI-DNR.

I’ve also seen a number of questions about aerial sprays for spongy moth.  This year, the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) has been coordinating aerial spraying in the western parts of the state to slow the overall spread of this invasive species.  The treatment used in early-season aerial sprays (Bacillus thuringiensis kurstaki) is most effective against small caterpillars.  Later spraying will focus on disrupting the ability of adult moths to successfully find a mate.  In theory, members of the public could band together to coordinate aerial spraying in their local area, but the planning process for this can take months.  By the time folks were posting on social media expressing a desire for aerial treatments in their neighborhood, that option was no longer feasible.  

One key thing to pay attention to later this summer will be the egg masses laid by adult female spongy moths. Each egg mass can contain upwards of 1,000 eggs, so surveying for egg masses can give insight into what the spongy moth situation could be like in 2023.  Those egg masses will also remain in place for roughly nine months until they hatch next spring, which gives lots of time for a search-and-destroy scavenger hunt in your yard.

For additional information on managing spongy moths, check out the updated UW-Madison Division of Extension factsheet on this insect and the Extension spongy moth website with month-by-month recommendations. 

 

What’s Eating My Roses in Spring? — Sawflies

If you’re seeing insect damage on your roses this spring, you aren’t alone and there are a number of early-season insect that can catch our attention.  For example, a number of caterpillars can occasionally be spotted on roses in spring, such as the rose plume moth (Cnaemidophorus rhododactyla).  There’s also the non-native rose leafhopper (Edwardsiana rosae) which can cause faint speckling on leaves. Later in the growing season, rose chafers (Macrodactylus subspinosus) and the notorious Japanese beetle (Popillia japonica) can be a concern.

Perhaps the most noticeable damage to roses in spring is caused by the larvae of sawflies.  These insects cause two types of damage: “windowpane” damage when they only feed partway through foliage and leave the upper leaf surface intact or small holes or notches when larger larvae chew entirely through the leaves.  In the Midwest, there are three different species of sawflies that can commonly be encountered on roses in spring: the roseslug sawfly (Endelomyia aethiops), the curled rose sawfly (Allantus cinctus), and the bristly roseslug sawfly (Claudius diffiformis).  To the naked eye, the larvae (up to ~ ½ inch long, pale greenish, and caterpillar-like) and the adults (~ ⅓ inch long, dark-colored, and wasp-like) all look similar.  However, determining the exact species under magnification can be helpful to understand the potential impacts on your roses.

Classic “windowpane” damage caused by sawfly larvae on roses. This damage occurs when small sawfly larva only feed partway through the leaves. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

The roseslug sawfly (Endelomyia aethiops) is the commonest of the three sawflies that I see samples of at the UW Insect Diagnostic Lab.  The larvae of this species have a smooth texture and brownish head capsule; their bodies are translucent and they usually have a pale greenish color due to ingested green leaf material.  Some good news about the roseslug sawfly is that this species only has a single generation in spring.  Their damage tends to be mostly just a minor cosmetic issue.  As the plants really take off in late spring, they tend to “shrug off” this damage and it’s quickly covered up by new growth.

Larva of the roseslug sawfly (Endelomyia aethiops) feeding on the underside of a rose leaf. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

The curled rose sawfly (Allantus cinctus) goes through two generations early in the growing season.  Similar to the roseslug sawfly, their feeding damage tends to be minor and plants are usually able to chug along just fine.  The larvae of the curled rose sawfly also are pale green with a brownish-orange head capsule.  They do have tiny spots on their bodies, but these are only visible under high magnification.  This species tends to feed while curled up and they also chew notches on the edges of leaves which can help distinguish this species from the other two sawflies.

Larva of a curled rose sawfly (Allantus cinctus) on the underside of a rose leaf. Note the notches on the edges of leaves which can serve as a clue to help identify this species. A rose leafhopper nymph is also present to the left of the larva. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

The third sawfly commonly seen on roses also tends to be the most problematic—the bristly roseslug sawfly (Claudius diffiformis).  Unlike the first two sawflies, this one can continue to reproduce throughout the growing season.  Because they go through many generations per year, their damage can accumulate over time and tends to be more notable.  Like the other two sawflies, the larvae of this species are also pale green with a brownish head capsule, but they are covered with fine, hair-like bristles when viewed under magnification.  Very few sawflies have a hairy or bristly appearance like this, which helps distinguish this species on roses.

Larva of the bristly roseslug sawfly (Claudius diffiformis). Note the fine hair-like bristles which help identify this species as seen in this magnified photo. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

If you do bump into these sawflies on your roses in spring, they’re pretty easy to deal with.  Options for managing them include:

  1. Do nothing. Since damage from the roseslug and curled rose sawflies tend to be minor, established plants often tolerate these insects with little/no intervention.
  2. Squishing, hand-picking or knocking them into a container of soapy water (be mindful of thorns…)
  3. Insecticidal soap or horticultural oils such as neem oil.  Make sure to achieve good spray coverage.
  4. Pyrethrins or spinosad—both are organic spray options. Note that Bacillus thuringiensis kurstaki (which works well against caterpillars) does not work against these sawflies.
  5. Conventional sprays from the hardware store/garden center labelled for use on ornamental shrubs and landscape plants.  Use caution since these products tend to have broader-spectrum of activity and can pose greater risks to bees and other pollinators such as butterflies, moths, beetles, and many flies.

  

A New Tool To Help Track Invasive Insects in Wisconsin

The United States Department of Agriculture (USDAdeclared April to be Invasive Plant Pest and Disease Awareness Month. To support this effort, the University of Wisconsin Insect Diagnostic Lab recently launched a new Wisconsin invasive insect mapping page to help track invasive insects in the state.

If you’ve followed this blog for a while, you’ll notice that quite a few of my posts focus on invasive insects.  Why?  In part, it’s because these non-native insects tend to be new or emerging issues and a key role of the UW Insect Diagnostic Lab is to help identify and track new and trending insects in the state. In addition, these invasive insects can sometimes cause significant damage or capture our attention for other reasons.  In a typical year, I see 2-3 new non-native insects show up in Wisconsin, which really adds up over time.  For every species that has arrived here, many more are making progress towards the state (e.g., spotted lanternfly). In other cases, non-native insects show up completely out of the blue.

What’s the big deal with non-native insects?
Non-native insects can cause harm in many different ways:
Introducing the new mapping page:

Because of the impacts mentioned above, it’s helpful to track invasive species so we can better understand where they may be having impacts, and also to get the word out about new detections and allow folks to take appropriate action.  To help in this regard, the IDL’s new invasive insect mapping page hosts a series of maps showing the known county-level distributions of a select list of invasive species.

These particular species have been included due to their relatively recent arrival in Wisconsin, and the ability to track them on a county-by-county basis.  Keep in mind that many other non-native insects can be found in the state, but some of these have been around a long time, are now widespread, and tracking on a county-by-county basis is no longer feasible or helpful (e.g., Japanese beetle, European paper wasps, German yellowjackets, European earwigs, and many more).

The maps on this page will be updated when new detections occur, and additional species maps will be added over time.  If you believe that you’ve observed one of the listed insects in a county where it has not been documented or a new invasive insect species, please collect evidence (physical specimens and/or digital images) and contact me to work on officially confirming the detection.  An example entry from the map page can be found below:

Example entry from the new Wisconsin Invasive Insects Mapping page

Spongy moth: an old pest with a new name

The spongy moth, Lymantria dispar has recently been in the news because of its new name. If you haven’t heard of the “spongy moth” before, it’s probably because you learned of this insect as the “gypsy moth”. It’s the same exact creature, just with a new common name.

Why the change? The word “gypsy” in this insect’s name was originally a reference to persons of Romani descent—“the popular name of the gypsy was no doubt suggested by the brown, tanned kind of color of the male” [Forbush & Fernald, 1896]. In 2021, the Entomological Society of America’s Better Common Names Project started to review the common names used to communicate about insects. Common names that include derogatory or inappropriate terms are being assessed. After a lengthy review process, the term “spongy moth” was ultimately decided upon to describe Lymantria dispar—and fittingly so. The beige egg masses of this insect have a soft, spongy consistency. In French-speaking parts of its range, this species has long been known as La Spongieuse for this very reason. Thus, you’ll be hearing more about the “spongy moth” over time as the term “gypsy moth” is phased out from educational/government websites and other resources.

Spongy moth caterpillar. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

In addition to the name change, the spongy moth should be on our radar for other reasons. Despite being in Wisconsin for decades, this pest can still be a serious defoliator of hardwood trees, both in yards and forested areas. From the period of 2014 – 2020, spongy moths haven’t been much of an issue. An important reason for this is a beneficial fungus known as Entomophaga maimaiga. This fungus was introduced from Japan and it is strongly associated with the spongy moth. Although it took some time to make an impact in the US, this fungus is now viewed as an important “check” on spongy moth populations. Spring rains encourage this fungus, which can cause high mortality amongst spongy moth caterpillars. However, in many parts of Wisconsin we saw an unusually dry year in 2021 which likely curbed the impacts of this fungus. As a result, I saw an increase in cases and reports of spongy moth caterpillars and their damage, adults, and egg masses at the UW Insect Diagnostic Lab last year and Wisconsin also saw a subtle uptick in defoliation of forested areas.

Defoliation (acreage) due to the spongy moth in Wisconsin over time. Source: Wisconsin DNR Forest Health 2021 Annual Report

As illustrated in the chart above, spongy moth populations can be very dynamic and can explode under the right conditions—leading to extensive defoliation. The egg-laying strategy of this species plays an important role in this dynamic. Adult female spongy moths deposit egg masses that can easily contain upwards of 1,000 eggs. In late summer and fall of 2021, I saw plenty of reports where trees contained dozens of egg masses, which could turn into tens of thousands of hungry caterpillars this spring.

Adult female spongy moth depositing eggs. The spongy beige egg mass can easily contain 1,000 or more eggs. Photo credit: Ryan Hodnett via Wikipedia.

Luckily, there’s still a bit of time to take advantage of this knowledge as the young caterpillars typically don’t become active until late April or early May. In the meantime, removal or destruction of the egg masses could help reduce local populations. While often found on trees, the egg masses can also be located on just about any surface in a yard—stacked boards, sides of structures, piles of firewood, and even on vehicles. Don’t delay if you noticed spongy moth activity in your area last year, since it won’t be long before the caterpillars are out and active this spring.


Reference: Forbush, E. H. and C.H. Fernald. 1896. The gypsy moth. Porthetria dispar A report of the work of destroying the insect in the commonwealth of Massachusetts, together with an account of its history and habits both in Massachusetts and Europe.  Boston, Wright & Potter. 495pp.

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 5/27/20: 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. Update 12/20: No substantial changes by the end of 2020—in North America, AGHs are still only known from far northwestern Washington State and nearby parts of British Columbia.  This insect has not been documented anywhere outside of that range. 


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 full-size version.

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