“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.
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While scorpions are common in southern parts of the US, they aren’t native to Wisconsin or the Upper Midwest. Occasionally, they show up in the state as hitchhikers from other locations. In the last decade, I’ve seen only a handful of cases where scorpions were spotted in the Badger state. Interestingly, I’ve now had three reports of live scorpions submitted to the UW Insect Diagnostic Lab this year—from Milwaukee, Madison, and recently from Prairie du Chien (as shown in the video clip below). In the rare cases that scorpions do make an appearance, they tend to be the striped bark scorpion (Centruroides vittatus) or a close relative.
The striped bark scorpion is one of the most commonly encountered scorpions in the United States. This arachnid can reach lengths of roughly 2½ inches. It typically has a beige or yellowish body with two dark stripes running down its back—hence the name. They also have a dark triangular pattern near the eyes at the front of the body, which can help distinguish them from other species.
The striped bark scorpion is primarily found in the south-central United States, with most sightings coming from Texas. Its range extends west to New Mexico and eastern Colorado, and as far northeast as the St. Louis area. The species is also present in Mexico. Occasional sightings have been reported outside this typical range. In their natural habitat, these scorpions prefer secluded spots such as under loose tree bark, logs, rocks, and woodpiles. They may also seek shelter near buildings and can inadvertently wander indoors.
Like many other scorpions, striped bark scorpions are nocturnal and are mostly active after dark. These arachnids are generalist predators, hunting insects and other small arthropods. They use their pedipalps (“pincers”) and telson (“stinger”) to subdue prey. While technically venomous, the striped bark scorpion’s venom is relatively mild and not considered medically dangerous to humans. However, stings from this species can still be quite painful.
Do the three reports of live scorpions mean that these creatures are becoming more common in our area? No, not necessarily. While it’s hard to tell how the range of scorpions may push northwards with climate change, we’re still well north of the native range of species like the striped bark scorpion. The vast majority of Wisconsinites will never see one of these creatures in the state outside of captivity. If anything, the three cases this year may simply illustrate how scorpions can be moved around by humans under the right conditions.
Now that the solar eclipse has passed, the next big natural phenomenon in Wisconsin will be the emergence of Brood XIII periodical cicadas in late May and June. These insects last emerged in the state in 2007 around the time that Steve Jobs was releasing the very first iPhone. While there were some reports of out-of-sync “stragglers” a few years ago, 2024 will be the year of their big emergence. Since these insects emerge every 17 years, you might only have a handful of opportunities to see them in the Badger State in your entire life. Despite having grown up in southeastern Wisconsin and turning 40 next year, I still have not witnessed an emergence myself and I’m really looking forward to this year’s activity.
With all the “buzz” about these amazing insects, I recently developed a new Wisconsin Periodical Cicada Website: cicadas.wisc.edu. This site covers the biology, ecology, and distribution of these insects, with lots of photos, audio recordings, cool historical videos, and other resources.
I also wanted to get a clearer picture of where these insects occur in Wisconsin. This winter, I dug through 150+ years of books, newspaper columns, university and government reports, and specimens in our very own Wisconsin Insect Research Collection to develop an updated map for the state. While this map is an improvement over older ones, there’s still plenty to learn about the local distribution of these cicadas in Wisconsin. To that end, I also launched a community science project on the website for participants to submit their own sightings from the state. It’s a brief fillable form and photos can be uploaded right from your phone, tablet, or computer—no app required. I’d love to receive any reports of periodical cicadas from Wisconsin this year to help improve our map of them in the state.
If you’re a cicada enthusiast and have a lot of reports to share, feel free to contact me via email (pliesch@wisc.edu) to discuss other arrangements. If you’re unsure if you’ve spotted a periodical cicada, check out the website’s Cicada Basics page or reach out for assistance at the UW Insect Diagnostic Lab.
Lastly, if you’re hoping to see and experience the periodical cicadas for yourself, your best bet would be to visit the Lake Geneva area in June. This part of the state has a very long and well-established history of periodical cicada activity. There’s also an updated Wisconsin map and a summary for each county on the periodical cicada website’s When and Where page. Previously, much of this information was buried in the literature, so the Wisconsin Periodical Cicada Website offers a unique look at the known distribution of these insects in the Badger State.
Check out cicadas.wisc.edu for additional details and get ready for all the buzz this spring!
Ask the Experts: A Monthly Garden and Landscape Q&A Series Sponsored by the UW-Madison Division of Extension Horticulture Program
Join our monthly online programs in 2024 for an opportunity to connect with plant health experts from the UW-Madison Division of Extension. Each session, held on Monday afternoons from 1:00-2:00 PM, is your chance to ask questions about your trees and shrubs, garden vegetables and ornamentals, lawns and more. Whether it’s about plant diseases, insects, or the selection and general care of plants in and around your home, our panel of seasoned experts will provide you with insightful answers. Don’t miss out on this opportunity to cultivate your knowledge and keep your plants thriving.
These online sessions are free but registration is required for each one that you would like to attend (see links below). Upon registration you will receive an email confirmation with the link for joining the session. All sessions are Mondays from 1:00-2:00 PM.
January 22, 2024 To register for this session, click here.
February 19, 2024 To register for this session, click here.
March 18, 2024 To register for this session, click here.
April 22, 2024 To register for this session, click here.
May 20, 2024 To register for this session, click here.
June 17, 2024 To register for this session, click here.
July 22, 2024 To register for this session, click here.
August 19, 2024 To register for this session, click here.
September 23, 2024 To register for this session, click here.
October 21, 2024 To register for this session, click here.
November 18, 2024 To register for this session, click here.
December 16, 2024 To register for this session, click here.
Note: As of late 2023, elm seed bug (ESB) has not yet been found in Wisconsin, but could show up in our area in the near future.
The elm seed bug (Arocatus melanocephalus | Hemiptera: Lygaeidae) is an invasive insect species native to parts of Europe. It was first detected in North America in 2012 in western Idaho and is now established in western parts of the continental US and Canada. In the eastern US, we haven’t seen much of this insect yet. It was technically spotted in the general Detroit area in Michigan in 2015 and reports continue to pop up in southeastern Michigan. This last summer, I helped confirm the presence of the elm seed bug (and the Asiatic garden beetle!) in the Twin Cities area for the Minnesota Department of Agriculture. Given the proximity to the Wisconsin state line, the elm seed bug could make an appearance in our state in the not-too-distant future.
Overall, elm seed bugs have habits similar to boxelder bugs and birch catkin bugs in that they feed on trees outdoors before invading structures later in the year. True to its common name, the elm seed bug is associated with elm trees and is especially fond of feeding on the seeds. They have little overall impact on the health of the trees. Later in the year, adult elm seed bugs seek out sheltered overwintering spots. In natural settings, they would typically overwinter beneath loose bark of trees or similar locations. However, they can readily invade homes and other structures in large numbers. Indoors, elm seed bugs are harmless to humans, but can be a general nuisance. Like brown marmorated stink bugs, elm seed bugs can also produce an unpleasant odor when crushed. Because ESBs are a nuisance invader like boxelder bugs and multicolored Asian lady beetles, management is going to be very similar and should focus mostly preventing these insects from getting indoors, e.g., physical exclusion and exterior crack and crevice treatments.
Since we have not yet seen elm seed bugs in Wisconsin, having this insect on our radar and being able to recognize it are the most important things at the moment. Elm seed bugs are similar in body shape to boxelder bugs, but are slightly smaller at roughly ¼ – ⅓ inch long. The adults are a dark brownish-black color with rusty-colored patches behind the head. There is a blackish, triangular structure (scutellum) on the middle of the back which sits within a rusty-colored, square-shaped patch. The edge of the abdomen is marked with a series of small, pale spots and the underside of the abdomen is a rusty, reddish color as well.
Wisconsin residents believing that they’ve found elm seed bugs are encouraged to collect a sample and contact me at the UW Insect Diagnostic Lab to definitively confirm the identity of the specimens: insectlab.russell.wisc.edu.
As one of the coordinators of Wisconsin Insect Fest, I’m thrilled to announce that Insect Fest will be back this year and is coming to the Upham Woods Outdoor Learning Center (Wisconsin Dells) this August. The event will be held from 2–10 PM on Saturday, August 19th, 2023 and is free and open to the public. A family-style cookout will be provided to participants (please RSVP if interested). Insect enthusiasts of all ages are welcome to attend!
Wisconsin Insect Fest is a celebration of insects and attendees will have the opportunity to learn about the different types of insects found in Wisconsin and the many important roles they play in the environment. Insect Fest will feature a variety of indoor and outdoor activities suitable for insect enthusiasts of all ages, including educational presentations, hands-on activities, guided insect hikes, live insects, and an informal BioBlitz activity. This is also a great opportunity to meet entomologists and learn about what they do.
The Wisconsin Insect Fest is a family-friendly event, and we encourage everyone to attend and learn about the fascinating world of insects. We hope to see you there!
For additional information about Wisconsin Insect Fest, visit: entomology.wisc.edu/outreach/wisconsin-insect-fest/
Spongy moth (Lymantria dispar) season has officially begun here in Wisconsin. Earlier this week (May 3rd), the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) Pest Survey Program reported caterpillars emerging from an egg mass in far southwestern Wisconsin. Based on forecasting models from the USA Plant Phenology Network, we should expect to see caterpillar emergence begin across much of southern Wisconsin over the next week. As things continue to warm up, the pattern will push further north in the state.
We may be facing a challenging year from this invasive insect. Dry conditions suppressed a beneficial fungal disease (Entomophaga maimaiga) the last two years and allowed spongy moth populations to build up. Along these lines, DATCP reported a 102% increase in male spongy moths caught in trapping surveys last year. Likewise, the Wisconsin Department of Natural Resources (DNR) Forest Health Team reported a significant uptick in defoliation last year—from 294 acres defoliated in 2021 to over 85,000 acres defoliated in 2022.
At this point in the season, it’s hard to know how much damage will ultimately occur on yard and forest trees in 2023. However, you can get an estimate of potential defoliation in your own yard by counting egg masses. Each overwintered spongy moth egg mass contains upwards of 1,000 eggs, so a yard with dozens of egg masses could soon face tens of thousands of hungry caterpillars in the near future.
Over the next few weeks, we can expect spongy moth caterpillar activity increase. These small caterpillars will cause a trivial amount of damage at first but will gradually become larger, hungrier, and more damaging over time. Keep an eye out for activity in your yard. If you are inundated with caterpillars, consider using sticky barrier bands and burlap barrier bands to trap them as described on the UW-Madison Extension Spongy Moth website.
Looking at the bigger picture, Mother Nature could hold a trump card for our spongy moth situation. If we end up having a rainy spring, damp conditions could encourage the fungal disease Entomophaga maimaiga to kick in and crash spongy moth populations (this halted outbreaks in SE Wisconsin in 2004 and 2010) . However, if we experience another dry season, it could allow spongy moth populations to build further—stay tuned and hope for rain!
When most folks think of “cutworms” they probably envision big fat caterpillars munching on plants in their yards and gardens. Sure enough, we have many species from the cutworm & armyworm family (Family Noctuidae) that can be notable crop pests, such as black cutworm, bronzed cutworm, variegated cutworm, true armyworm, fall armyworm, and others. Readers should keep in mind that the Family Noctuidae is surprisingly diverse with over 2,500 species known from the US and Canada. Many of these species play important roles in the food web and can be as important as bees for pollination of certain crops!
While cutworms can be common during the summer months into the fall, we usually don’t expect to see them this time of the year. Surprisingly, there’s one cold-hardy species that has been common in Wisconsin recently—the “winter cutworm” (Noctua pronuba). This species gets its name due to the fact that the caterpillars are cold-tolerant and can be active when temperatures dip. While they won’t be out-and-about during a polar vortex, I’ve had many recent reports at the UW Insect Diagnostic Lab of winter cutworm caterpillars wandering on the snow when temperatures have been in the 20’s. Overall, there are very few caterpillars that venture onto the snow, period.
Similar to other cutworms, the winter cutworms are plump, earth-toned caterpillars—they are brownish with pairs of black dashes bordered by white running down the sides of their backside, which makes them easy to identify. (Technically, a greenish form of the caterpillars also occurs). In addition, if you see any caterpillar that even looks “cutworm-like” out on the snow, it’s almost certainly this species. They pass through the the winter as nearly-mature caterpillars before pupating in the spring. The adult moths are active during the warmer months and display an amazing array of different color forms—ranging from very light beige to grey or brownish—although the hindwings (typically tucked under the body at rest) are a diagnostic yellow color. Thus, adults are commonly known as “large yellow underwing” moths.
The winter cutworm can be found from coast-to-coast in much of the US and Canada, although this wasn’t always the case. This species is common in Europe and wasn’t known from North America until 1979 when it was first spotted in Nova Scotia. While the caterpillars do feed on a wide range of plants, they’re rarely a notable pest. Outbreaks and reports of damage aren’t common, although there was a notable outbreak in Michigan around 2007-2008. In most cases, these caterpillars are simply a curiosity as they wander across the snow on mild winter days—sometimes by the thousands. In addition, winter cutworms can occasionally sneak into structures as well, which can be another surprise to see caterpillars actiely wandering in garages or barns when the temperature is in the 40’s.
Each insect species has a “story” to tell—where they came from, what they do, and what their presence means for humans. Knowing this story can make a big difference when it comes to our own actions. For example, imagine finding an insect near your bed. If you recognized the insect as a harmless ground beetle that accidentally snuck in from outdoors, you might shrug your shoulders and carry it outside in a Tupperware. But, if the insect were a blood-feeding bed bug, it could mean an expensive bill to have your home professionally inspected and treated by a pest control company. Knowledge is power!
In my mind, the first step towards getting this knowledge is through proper identification. I say this with a certain amount of endearment, as I am an insect diagnostician after all. However, once you’ve properly identified an insect, it’s easy to look up its “story” (biology, behavior, etc.) in books, websites, or even the scientific literature. This process can allow you to more efficiently identify the root of a problem (if there is one) and figure out a solution.
A good example of this concept would be flies in and around homes. There are easily dozens of different types of flies that can be encountered in typical yards and homes in the Midwest and each has a slightly different story to tell. Some can breed in piles of grass clippings or seaweed (e.g., stable flies), some parasitize earthworms but like to sneak indoors (e.g., cluster flies), and others can hitchhike on plants. A common and widespread group of flies is the Family Calliphoridae—the blow flies.
Luckily, blow flies can be identified easily in many cases due to their metallic green or bluish coloration. Some members of this group are even known as “green bottle flies” or “blue bottle flies” due to their distinctive colors. Overall, the blow flies are mid-sized flies and are often slightly larger than house flies (~1/4 – 3/8” long). The larvae are your stereotypical pale and slender “maggots”, although they can be definitively distinguished from similar-looking fly larvae under the microscope.
When blow flies are found indoors, it’s often easy to understand the situation and remedy the problem. One of the biggest factors in the “story” of blow flies is dead stuff. Out in nature, blow flies play an incredibly important role in helping break down dead animal matter. These flies are often the very first insects to show up at dead animals—sometimes within seconds. After laying eggs, the resulting larvae do a lot of work feeding on and breaking down animal tissues. Being poikilothermic (“cold-blooded”), they also develop at a predictable rate depending on the temperature, so these flies are even used to estimate lengths of time in forensic investigations.
There’s always a chance that a blow fly spotted indoors might have accidentally snuck in from outdoors, but in many cases it’s an indication of something dead. Blow flies are able to detect the faint odors of death from long distances, so a single dead mouse, bat, or other creature in a home can attract these flies. Rather than spraying an insecticide, the best remedy is to find the root of the issue and clean it up. In many cases, it’s just a matter of checking mouse traps and discarding the mouse that had recently met its demise.
Another situation that I often see indoors is a scenario that has simply proceeded further than the last one. If an adult female blow fly is able to locate a dead mouse (or other animal) and lay eggs unnoticed, the resulting larvae can consume most of the remains and complete their development. If this happens, the first thing noticeable is often a bunch of maggots wandering the nearby area (the maggots often wander away from their food source when ready to pupate). When they pupate, small brownish “pods” (puparia) may be noticed and upon reaching maturity, dozens of adult blow flies can seemingly appear out of nowhere. In such a case, it’s generally an indicator that a dead mouse or other animal had been present for some time (often a few weeks). Unless there are additional resources for them, these flies usually perish quickly indoors. This scenario frequently comes into play in second homes or cabins that are unoccupied for longer periods of time or if the dead animal is location in a tucked away or inaccessible spot (such as in a wall or ceiling void).
If you’re like me, you’ve probably been out appreciating our recent fall weather. Likewise, boxelder bugs (Boisea trivitatta) have also been enjoying the warmth. I’ve seen an uptick in reports of boxelder bugs at the UW Insect Diagnostic Lab this year compared to most other years in the last decade and weather patterns in the Midwest have played an important role.
Whether you recognize them or not, there’s a good chance you’ve bumped into boxelder bugs before. These black and red insects can be common throughout the warmer months and can be especially abundant in late summer and early fall. Adults are approximately ½ inch long and have a criss-cross pattern on their backside created by their wings. Juveniles (nymphs) are smaller with much more red on their bodies. As the nymphs mature, their developing black wing pads become noticeable. True to their name, boxelder bugs are commonly associated with boxelder trees (Acer negundo). Botanically speaking, boxelders are technically a type of maple, and some other maples can also be a host for these insects as well as ash trees and a few others.
From a plant-health perspective, boxelder bugs cause little damage to plants and are of little concern. These insects get the most attention when they’re spotted on the sides of homes and other structures. They’re often particularly fond of the southern and western sides of homes where the warm afternoon sun hits. Boxelder bugs are often spotted on buildings in fall as they search for sheltered overwintering spots. If they can squeeze in through a gap or crack, they can easily hunker down in a wall void, or similar spot for the winter. Sometimes, boxelder bugs can make it to a location where they become active indoors during the winter months, much to the chagrin of the humans living in the home. While these insects can be perceived as a nuisance, they’re really quite harmless to people, pets, and homes (although they could stain light-colored fabrics if crushed). Like other “fall invading” insects (e.g., cluster flies, multicolored Asian lady beetles, brown marmorated stink bugs, and western conifer seed bugs), a helpful approach is to seal up potential entry points on the exterior of your home before these insects make their way inside.
Looking at long-term patterns, boxelder bug populations have generally been low in many parts of Wisconsin over the last decade. A reason for this is moisture. When we have rainy years, entomopathogens (insect-infecting pathogens) can keep boxelder bug populations low. In contrast, boxelder bugs tend to thrive under drier and warmer conditions. There’s even been research on a closely-related species (the western boxelder bug, Boisea rubrolineata) in the western US suggesting that those insects deliberately sunbathe and secrete a chemical to help inhibit the common entomopathogenic fungus Beauveria bassiana. Here in Wisconsin 2021 was surprisingly dry in many areas which likely helped boost boxelder bug numbers. Likewise, some parts of Wisconsin also saw dry conditions continue into 2022, which may have helped them further, leading to an increase in boxelder bug populations and reports this year.
With the arrival of fall, we’re starting to see pumpkins, spooky yard decorations, and pumpkin spiced everything (*shudder*). Not to be left out of the festivities, one insect can be quite noticeable this time of the year—the large milkweed bug (Oncopeltus fasciatus).
If you’re wondering, we do also have a small milkweed bugs (Lygaeus kalmii), although it’s not usually as common as the ubiquitous, larger cousin. Both juveniles (nymphs) and adults of the large milkweed bug are fittingly adorned for fall. Adults reach lengths of nearly 3/4 inch long and are mostly orange with black patches on the wings and body. Going through “simple metamorphosis” (technically, they’re paurometabolous), the juveniles or nymphs look similar in body shape to adults (although smaller) and are also orange with some black. In more mature nymphs, the developing blackish wing pads are quite noticeable. When you see a group of nymphs and adults hanging out on milkweed in the fall, it’s easy to recognize that they’re all the same species.
Large milkweed bugs specialize on milkweed plants and are one of the many creatures that can be found in and around milkweed patches. When they feed, large milkweed bugs use their sucking-type mouthparts to sip fluids from plants; they’re especially fond of the developing seed pods and are often spotted on pods. While home gardeners hoping to rear monarchs might be concerned about competition, these insects generally cause little harm to plants and are more of a curiosity than a pest.
Large milkweed bugs have a very seasonal pattern in the upper Midwest. They can’t survive the winter at more northern latitudes, so they must migrate northwards each year. Here in Wisconsin, you’d be hard pressed to find large milkweed bugs in spring, but by July they’ve often arrived in low numbers. Large milkweed bugs can become quite common by late summer and early fall as it typically takes 40+ days for a new generation of adults to appear from eggs laid in our area.
In much of Wisconsin, we’re just starting to see foliage change to reds, oranges, and yellows, but as you’re out enjoying the fall weather, keep an eye out for these festive-looking insects around milkweed patches.
