“What’s Crawling in the Lab?” is a blog featuring short stories, pictures, and highlights from the UW-Madison Insect Diagnostic Lab. Topics range from the insects most commonly diagnosed in the lab to emerging arthropod pests and unique and bizarre cases from the lab.
You can subscribe to the blog using the subscription box in the left hand menu bar. Subscribers will be notified by email when new posts are added.
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.
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.
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.
Another variable that could be at play this year is a beneficial fungus known asEntomophaga 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.
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.
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 (Cnaemidophorusrhododactyla).There’s also the non-native rose leafhopper (Edwardsianarosae) which can cause faint speckling on leaves. Later in the growing season, rose chafers (Macrodactylus subspinosus) and the notorious Japanese beetle (Popilliajaponica) 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 (Endelomyiaaethiops), 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.
The roseslug sawfly (Endelomyiaaethiops) 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.
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.
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.
If you do bump into these sawflies on your roses in spring, they’re pretty easy to deal with.Options for managing them include:
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.
Squishing, hand-picking or knocking them into a container of soapy water (be mindful of thorns…)
Insecticidal soap or horticultural oils such as neem oil. Make sure to achieve good spray coverage.
Pyrethrins or spinosad—both are organic spray options. Note that Bacillus thuringiensis kurstaki (which works well against caterpillars) does not work against these sawflies.
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.
The United States Department of Agriculture (USDA) declared 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:
Be an aesthetic or nuisance issue (e.g., European earwigs, German yellowjackets, etc.)
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:
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.
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.
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.
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.
Unbeknownst to most students, employees, and visitors at UW-Madison, there’s a room of flesh-eating beetles on campus.An unmarked door on Bascom Hill leads to the chamber more formerly known a the Dermestarium, which serves a rather peculiar yet specific purpose. No need to worry though—this isn’t 1999’s The Mummy. Rather, these insects are actually quite helpful in the way that they’re used.
Most insects are actually helpful in one way or another and provide ecosystem services as pollinators, predators, parasitoids, decomposers, or in other roles.Humans have also figured out some pretty unique ways in which insects can help us out.For example, mealworms can eat and break down certain types of plastics and are being looked at as a way to help reduce man-made waste materials.In the legal realm, knowledge about insects is used to help solve crimes—a field known as forensic entomology, which dates back nearly 1,000 years.In the case of UW-Madison and many other universities and museums, a specific type of beetle is used to help clean skeletal remains for research, teaching, and display in zoological museums.
The beetles in the UW Dermestarium are known as hide beetles (Dermestes maculatus) and they’re especially fond of dried-out, protein-rich materials such as remnants of muscles, sinew, fur, feathers, and similar materials.Out in nature, such insects do play a role in the natural break down of animals remains—but not right away.Rather, much of that initial work is left to the larvae (maggots) of blow flies (Family Calliphoridae) and flesh flies (Family Sarcophagidae).Hide beetles and close relatives from the “carpet beetle” group (Family Dermestidae) show up days, weeks, or even months later once the remains are drier.
In a museum setting, hide beetles can be helpful in the preparation of skeletal remains.With their small size (roughly 1/4-inch long) , these insects use their mandibles to efficiently remove leftover bits of tissue from tiny nooks and crannies.For a human trying to prepare remains, such a task would be tedious and may not be feasible for some structures (such as the inside of a skull).However, a tank of these beetles can easily clean skeletal remains in a matter of days with relatively little effort required, other than maintaining correct ambient conditions for them.
Interestingly, hide beetles and close relatives like the larder beetle (Dermestes lardarius) can be found in our own homes as well.Their presence poses little risk to humans, but could indicate the presence of a dead rodent or bird in a structure.Such insects can also develop on a range of protein-rich materials ranging from dead insects in a window sill to human and pet foods and they can occasionally be a pest in home pantries. Historically, such insects were notable pests of dried meats and cheeses in storage. If you’re curious to know more about these and other insects associated with our homes and everyday lives, Richard Jones has an excellent book on the topic: House Guests, House Pests: A Natural Hisotry of Animals of the Home.
A more detailed history of UW-Madison’s Dermestarium can be found here.
Despite the season, there’s a surprising number of insects and related arthropods that can be found on the snow during the winter months here in the Midwest.Such creatures have fascinating life histories and special adaptations (such as natural “antifreeze”or cryoprotectants) that allow them to not only survive, but remain active at low temperatures.Even these adaptations have limitations and winter insects generally aren’t active if temperatures are below ~20˚F (-7˚C).Most activity occurs on mild winter days when temps close to or just above freezing.
If you’re curious to learn more about the stories behind these winter creatures and others, I’d encourage you to check out Bernd Heinrich’s Winter World: The Ingenuity of Animal Survival. Read on to learn about some of our commonest “winter” insects in Wisconsin and nearby states:
Snow Fleas: If you follow this blog, you might recall the example of snow fleas from two winters ago.These dark-colored springtails (Collembola) can sometimes be abundant enough to give large swaths of snow a sooty appearance.Snow fleas can be common on mild winter days and if I’m out cross-country skiing in the Northwoods, I’m often more surprised if I don’t spot any.
Snow Flies: One of the weirdest examples of a “winter” insect would be “snow flies” from the genus Chionea. Despite their spider-like appearance, snow flies are actually a type of wingless Limoniidcrane fly.Being wingless and generally slow moving might sound like an easy target for predators, but by being active at cold temperatures these insects can actually avoid the many predators that feed upon related flies during the warmer months.Interestingly, their physiology is so specialized, that these unusual insects can be active between about 20˚F (-7˚C) and 32˚F (0˚C), but if it’s a warm winter day with melting snow it can actually be too hot for them!If you’d like a more detailed look at these insects, check out J.R. Schock’s article in The Kansas School Naturalist.
Winter Crane Flies: I occasionally get reports of “swarming mosquitoes” on winter days, and perhaps you’ve bumped into a cloud of tiny delicate flies out in the snowy woods or on a mild fall or spring day.What you’ve likely encountered are winter crane flies (Family Trichoceridae).These delicate flies are related to mosquitoes but have no interest in blood.The adults are simply trying to mate and the larvae are scavengers.
Snow Scorpionflies: In my mind, one of the more elusive winter insects is the snow scorpionfly.Despite having “scorpion” in the name, these aren’t scorpions (or true flies for that matter).Rather, they belong to a small order of insects (Mecoptera), which includes some bizarre examples, such as the common scorpionflies, hangingflies, and earwigflies.Like the snow flies, the snow scorpionflies are also flightless and simply wander about on the snow when conditions are right.In the Midwest, we only have two species from this group Boreus brumalis and Boreus nivoriundus, and both species are associated with mosses.
Aquatic insects: If you’re near open streams or rivers during the winter months, certain aquatic insects can sometimes emerge and be found on the snow. Caddisflies and stoneflies are two of the commonest examples. I recall ice climbing one winter’s night at Governor Dodge State Park west of Madison and reaching the top of a frozen waterfall only to spot dozens of adult “aquatic” insects active on the snow.The conditions must have been just right that evening, as I also saw hundreds of tiny Cynipid wasps (from oak galls) on the snow as I descended the access trail from the climb.
Spiders: Hexapods aren’t the only arthropods getting in on the winter fun.Species from at least a half-dozen families of spiders can occasionally be spotted on the snow on mild winter days.They might be pretty lethargic, but it’s still interesting to see creatures like that out-and-about on the snow. The video clip below shows a spider I spotted on the snow in Northern Wisconsin on New Year’s Eve a few years ago when the air temperature was right around 30˚F (-1˚C).
What a year it’s been. Things seemed like they were getting back to normal this past summer, only for the Omicron variant to pop up and say—not so fast. Despite all the ups-and-downs, services have carried on at the UW Insect Diagnostic Lab in one way or another through the second year of the COVID pandemic. Things have changed a bit and these days I’m on campus much more than a year ago. Throughout the pandemic, demand for services at the IDL has remained high with over 2,400 ID requests in 2021.
Since COVID first popped up, there have been some subtle shifts in lab statistics—an increase in the percentage of samples solely involving digital images (vs physical specimens) and an overall increase in the proportion of cases coming from the public. Considering the pandemic, this makes sense. Over the last two years, campus buildings and the IDL have been closed to visitors at various points, meaning that clients couldn’t drop off samples. In other cases, it might have been tough to make it to a post office or the UPS store to ship a sample in. Likewise, with many folks working from home, it likely led to more time out in yards and gardens, or visiting local parks or hiking trails—and more time to notice insects.
Looking back at the cases from this last year, 2021 was a unique year due to our unusually hot and dry weather conditions in Wisconsin. Based on data from the Wisconsin State Climatology Office, Madison was quite warm and saw an extra ~500 growing degree days in 2021, but was down about 15 inches of precipitation for the year. Some parts of the state were even hotter and/or drier than Madison and most of the state was categorized as either unusually dry or in some stage of drought during the year [US Drought Monitor].
The weather conditions this year led to some shifts in the insects and related arthropods seen at the UW Insect Diagnostic Lab. A pest that had been relatively quiet the last decade, Lymantria dispar (formerly known as the “gypsy moth”), thrived with the dry conditions this past spring. In “rainy” years, a beneficial fungus (Entomophaga maimaiga) can “kick in” to help keep their numbers in check. If 2022 is another dry year, we could be in store for even more problems from this invasive species. Certain mites also thrived this year and I saw a large number of cases of eriophyid mites causing damage to plants ranging from coneflowers to garlic. Springtails weren’t necessarily more abundant (they feed on decaying plant matter and thrive under damp conditions), but I suspect the hot & dry conditions sent them looking for any place darker, damper, and cooler. This led to lots of reports as they were trying to invade structures.
We’ll likely continue to see the impacts of the 2021 drought for some time. Plants, including established trees and shrubs, also suffered from the drought and this will likely lead to an increase in reports of “secondary” insect pests in the next few years. Certain insects can be generally “well behaved” and leave healthy plants alone, only to attack stressed and weakened plants. As an example, cases of the two-lined chestnut borer (a notable pest of oaks) often increase 1-3 years after a drought, and I’m expecting to see more cases in the coming years.
In the realm of medical entomology, it was a good year for ticks both in Wisconsin and other parts of the US. Black flies (Family Simuliidae) had another strong year in many parts of the state, although calls about these were shifted a bit earlier than in previous years (likely due to an “early” spring). If there’s a silver lining to the drought, it’s that mosquito pressure was down in Wisconsin for much of the summer. As we received a bit more rain in the latter half of summer we saw some late season activity, but disease pressure remained low (only three West Nile Virus cases in Wisconsin, compared to 50+ in a “bad” year). As recreational and work-related travel increased a bit more in 2021 compared to 2020, I did see an uptick in reports of bed bugs.
With the Asian giant hornet garnering attention in the news for the second year in a row, I continued to see lots of reports of cicada killer wasps, pigeon horntails, great golden digger wasps, and other large insects. Unfortunately, with the sensationalized hype about “murder hornets” (ahem—New York Times…) I had plenty of reports of other large harmless insects that were killed simply because they “looked big and scary” (one particular photo of a tomentose burying beetle comes to mind…). Overall, the Asian giant hornet story was really pretty quiet this year, with a limited amount of activity in a small part of the Pacific Northwest. As of December 2021, the Asian giant hornet has not been found in Wisconsin or anywhere close to us.
I had plenty of reports of social wasps (yellowjackets, bald-faced hornets, and paper wasps) as well as bumble bees this year—including three reports of the endangered rusty-patched bumble bee in the same week in early August! We missed the Brood X “cicada craze” here in Wisconsin, but I still had plenty of questions about them from reporters. We will, however, see some periodical cicadas (Brood XIII) in 2024 in southern Wisconsin.
Serendipity can play a big role in being an entomologist or any kind of naturalist. Sometimes, you’re simply in the right spot at the right time to make an interesting observation or scientific discovery. There’s lots to learn about the natural world around us and plenty of room for discoveries.
Think about birds for a moment. According to the Wisconsin Society for Ornithology, there are 441 species of birds known from the state. Birders can spend an entire lifetime learning about the biology and habits of these species and how to identify them by sight, song, and other features. Now, think about insects. Here in Wisconsin, our best estimate is that we have somewhere in the ballpark of 20,000 insect species in the state (let alone all the other arthropods!). During talks to the public, I often joke that birders have it easy—with so many insects out there, you could have ten lifetimes and still have plenty to learn and discover!
With that said, there’s lots to be discovered in the world of insects. Even though I’ve been collecting and studying these creatures for over 15 years, I still make discoveries on a regular basis. This often requires hours of diligent observations and the ability to focus on the tiniest of details, but in other cases it comes down to plain old luck. For example, I’ve written about discovering and collecting specimens of the rare fly, Asteia baeta, in my house after setting up a Christmas tree (no such luck this year…).
A more recent example of entomological serendipity occurred this last July in my own backyard in Dane County. I was enjoying a cold beer on our back deck one warm evening when I noticed a few small scarab beetles on our window screens. Since I keep a lookout for invasive species as part of my job at the UW Insect Diagnostic Lab, I always have a list of species in mind that I’m keeping an eye out for. In this particular case, the beetles piqued my interest due to their resemblance to the non-native Asiatic garden beetle (Maladera formosae), although we have native species in the genus Serica that can look similar to the naked eye. Just a few weeks before this, I had identified some specimens of the Asiatic garden beetle from a suburb of Chicago, which placed the species on my immediate radar.
Hold my beer, I’m getting some vials. I collected all the specimens I could spot (4), and was able to confirm their identity as the Asiatic garden beetle after tracking down appropriate keys and dissecting out the male genitalia—a surprisingly common and delicate entomological task used to distinguish certain insects that look similar. While I’ve seen a possible report of the AGB on iNaturalist, the specimens from my back deck marked the first specimens of the Asiatic garden beetle collected and confirmed from the state of Wisconsin.
The Asiatic garden beetle first showed up in the United States in New Jersey in the early 1900’s and has spread westward ever since. This species is a notable pest and feeds on a wide range of plants. The adult beetles are “sneaky”—hiding by day and causing most of their damage after dark. They are primarily active on warm evenings (>70˚F) and can be strongly attracted to lights. In this case, not only was I enjoying a cold beer on a warm summer night, but the string of patio lights over our deck likely attracted the beetles from the nearby area. The larvae (white grubs) can be pests of turfgrass, home gardens, and agricultural crops such as corn and potatoes.
At this point, I have many more questions than answers about the Asiatic garden beetle and what the future holds for this species in Wisconsin. To date, only a handful of specimens have been collected (four in July and another specimen in mid-September) and no plant damage has been observed. However, I’ll be keeping a close eye on this species, since reports from nearby states suggest that we may be seeing more of this species and damage in the coming years.
On average, I see 2 – 3 new, non-native insect species show up in Wisconsin every year through my work at the UW Insect Diagnostic Lab (3 so far in 2021!). I’ve mentioned this in previous blog posts, but humans make excellent accomplices in moving species from one spot to another on the globe. This last spring, I saw one of the most interesting cases of my career which highlights this point exactly.
Like any good globetrotting adventure, this story involved a rugged, adventurous mode of travel—a Jeep. This particular Jeep had been imported in late 2020 and after a period of time in the eastern US, it eventually wound up in a small town in central Wisconsin. Unbeknownst to the owner of the vehicle, this Jeep also contained unexpected insect stowaways.
These insects managed to survive for months sheltered within the Jeep and would become active when the vehicle was in use—unexpectedly wandering out of nooks and crannies, much to the displeasure of the driver. Obviously, this isn’t something a new car owner wants to see, so a pest control professional was consulted about the insects and they got in touch with me at the UW Insect Diagnostic Lab to figure out what the specimens were. In the initial conversation, the mystery insects had been described as “stink bugs” and I figured that overwintering nuisance insects like the brown marmorated stink bug might have been involved. The photos, however, hinted at something far more puzzling.
By this point, I had been running the UW Insect Diagnostic Lab for six years and hadn’t seen anything quite like the insect in the photo. I requested a sample to get to the bottom of this mystery under the microscope. I handle so many cases at the diagnostic lab (~2,500 annually), that I can generally identify most specimens to family (or perhaps even genus or species-level) with a quick peek. In this case I was utterly perplexed, meaning I had to run it through a general family-level taxonomic key for the true bugs (Order Hemiptera). In Borror and DeLong’s Introduction to the Study of Insects the specimens keyed out to the Family Heterograstridae.
An asterisk is always a surprise when you encounter it in a taxonomic key. It generally means one of two things: you either took a “wrong turn” in the decision-making process (and misidentified the specimen) or it’s something rare or highly unusual. Something seemed amiss, so I consulted a few other keys to further confirm the Family Heterogastridae. In North America there’s only a single genus (Heterogaster) from this family and three species known from the west coast of the US. The specimens in my possession looked markedly different. Because the Family Heterogastridae is mostly a footnote in the western hemisphere, it’s hard to find information on this group of insects.
This is why geographic clues can be so important in diagnostics and why I request this information with every sample at the UW Insect Diagnostic Lab. Knowing where a specimen was collected and/or originated helps tremendously in learning more about it. Through follow-up conversations, I learned that the Jeep was manufactured in and imported from Melfi, Italy—meaning there was a good chance I was looking in the completely wrong hemisphere for the information needed to identify it.
This led to many evenings of armchair sleuthing. During this process, I’d like to imagine myself as Jason Bourne tracking down members of an international conspiracy while a suspenseful soundtrack blared in the background, but in reality I was mostly just locating pdfs of scientific papers and using Google Translate. Such work could have taken months or even years a few decades ago, but was now possible in the matter of a week or two.
Thanks to Interlibrary Loan and other online resources, I tracked down manuscripts from a half-dozen European and Middle Eastern countries in multiple languages and spent hours pouring over posts on Italian and French insect forums looking for clues. I finally found my answer in a scanned pdf version of Jean Péricart’s Hémiptères Lygaeidae euro-méditerranéens, vol. 1., which identified the specimens as Platyplax inermis—a species associated with Salvia spp. plants in the Mediterranean region.
It’s been hard to miss the recent news headlines about fall armyworms “FAW” (Spodopterafrugiperda). States east of the Rockies have seen historical outbreaks of this insect in 2021, including a bit of fall armyworm activity here in Wisconsin. In some cases, the caterpillars have decimated entire crop fields or home lawns overnight before marching onwards in search of “greener pastures”.
We usually don’t see much of the fall armyworm in Wisconsin and it’s primarily a pest of warmer areas, such as the gulf coast states. The FAW is native to tropical and subtropical parts of the western hemisphere and the larvae (caterpillars) can feed on dozens of different types of plants—ranging from field crops to fruits and vegetables and even turfgrass. They can be particularly important pests to crops such as corn, grains, and alfalfa.
The fall armyworm can’t survive the winters in the US, other than the southernmost areas (e.g., southern Texas and Florida). However, in spring and summer the adult moths migrate northwards and lay eggs. Over the course of many generations and subsequent northward migration, fall armyworms can make it to the upper Midwest and even parts of southern Canada. Historically, fall armyworm has rarely been a notable pest in Wisconsin or the upper Midwest—it simply arrives too late or in too small of numbers to be a concern. To a certain extent, every year is a roll of the dice, but the odds are usually in our favor in Wisconsin and other northern states.
This year has been different though, with large numbers being spotted northwards and reports of significant damage coming in from nearby states such as Illinois, Indiana, Iowa, and Ohio. Many other states ranging from Kansas to the mid-Atlantic region have also been impacted in the later parts of summer. While there have been scattered reports of fall armyworm damage to field crops in southern parts of Wisconsin, the lateness of this pest’s arrival and our declining temperatures have likely spared us from the widespread damage seen in other states.
Under hot conditions (e.g. temps in the 90’s), the life cycle of the fall armyworm—from eggs to adult moths—can take only a few weeks. However, fall armyworms are “cold blooded” creatures and cooler temperatures slow down their growth and development. Depending on how chilly it is, their life cycle can be “stretched out” to take 60 days or longer—leaving them much more vulnerable to predation, parasitism, or exposure to frosts.
One study* found that fall armyworm eggs didn’t hatch at all if temperatures were cool enough (though not particularly chilly by Wisconsin standards). That particular study simulated daytime/nighttime temperatures of 21˚C (70˚F) and 8˚C (46˚F)—temperatures that are “in the ballpark” for many parts of Wisconsin by mid-September and are often considered downright “pleasant” by Wisconsinites. Eggs held at warmer temperatures in the experiment hatched just fine.
For eggs that did hatch this year in Wisconsin, cool temperatures also could have helped us out by slowing down their development. As they grow, fall armyworms pass through six sub-stages (instars). The early instar caterpillars are so small, they simply can’t eat much and cause little damage. It’s not until FAW caterpillars become more mature fifth and sixth instars that they really start to chow down and cause significant damage to plants. Thus, falling temps could help prevent the fall armyworm caterpillars from making it to the destructive late instar stages and could also leave them more exposed to a variety of threats.
The fall armyworm outbreak of 2021 could very well be a “once every few decades” type of event, and our northern location likely helped us avoid the significant problems seen in other states. However, if changing climate gives the fall armyworm a “head start” by overwintering farther north, it’s possible that we could see more of this pest in Wisconsin in the future.
*Barfield, Mitchell, and Poe. 1987. A Temperature-Dependent Model for Fall Armyworm Development. Annals of the Entomological Society of America. 71(1): 70-74.