Category Archives: Outdoor Insect Invaders

Bugs, Invasive Species, Outdoor Insect Invaders, Tree Insects

Elm Seed Bug: A New Pest to Watch for in Wisconsin

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.

Elm Seed Bug Infographic
Infographic describing the main features of the elm seed bug (Arocatus melanocephalus). Infographic created by PJ Liesch, UW Insect Diagnostic Lab. Click for larger version.

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.

Bugs, IDL Highlights, Outdoor Insect Invaders

Boxelder Bugs: Back in the Mix

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.

Adult boxelder bug
Adult boxelder bug (Boisea trivitatta) on the side of a building. Photo credit: PJ Liesch, UW-Entomology.

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.  

Two juvenile boxelder bugs
Boxelder bug nymphs (juveniles) on the UW-Madison campus. Photo credit: PJ Liesch, UW Entomology.

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.

A number of adult boxelder bugs on a window screen.
Boxelder bugs congregating on the side of a home. Photo submitted to UW Insect Diagnostic Lab.

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.

Beetles, IDL Highlights, Outdoor Insect Invaders

Wandering Weevils: Summertime Visitors

If you’ve spotted small, crunchy beetles in your home this summer you aren’t alone.  Broad-nosed weevils (Curculionidae: Entiminae) have been a surprise this summer at the UW Insect Diagnostic Lab.  While I see cases of these insects every year, things have been a bit more intense this summer with a flood of reports from around Wisconsin.

What’s a weevil?  Out of the 100+ different families of beetles, the weevils (Family Curculionidae) are extremely diverse with over 50,000 species in this group alone.  In terms of their appearance, most weevils might remind you of Gonzo from the Muppets with their very pronounced “snouts”.  A great example of this in Wisconsin is the genus Curculio (the “nut and acorn weevils”).  Some species in this group can have a snout (technically “rostrum”) as long as the rest of their body.

The pecan weevil (Curculio caryae). The pronounced rostrum or “snout” is a classic feature of many members of the weevil family. Photo credit: Jennifer C. Girón, Museum of Texas Tech University. Bugwood.org.

On the other hand, some members of the weevil family lack the pronounced snout .  One such group, the subfamily Entiminae, is commonly referred to as the broad-nosed weevils.  Our common broad-nosed weevils tend to be small (around ⅛ – ¼ inch-long) and have pear-shaped bodies with very hard, crunchy exoskeletons; they also have “elbowed” antennae similar to ants.  The color of the broad-nosed weevils can vary by species, but many are blackish or grayish.

The imported longhorned weevil (Calomycterus setarius)—a type of “broad-nosed weevil” that occasionally sneaks indoors. Photo credit: Natasha Wright, Braman Termite & Pest Elimination, Bugwood.org

When it comes to broad-nosed weevils, we have over 100 species in the Midwest alone.  In general, these are “outdoor” species associated with plants.  The larvae tend to feed on the roots of plants while the adults often chew small notches out of the edges of foliage.  Interestingly, a few species in this group have the habit of sneaking indoors during the summer months.  Once inside, these insects are completely harmless but can be a minor nuisance as they seem to mindlessly wander on walls or floors.

During the summer months, some broad-nosed weevils can sneak indoors—occasionally in large numbers. In this case, hundreds of strawberry root weevils (Otiorhynchus ovatus) were wandering on the side of a home. Photo submitted to UW Insect Diagnostic Lab.

Conditions in Wisconsin over the last year and a half must have been just right for some of these species, since I’ve had a flood of requests to help identify broad-nosed weevils in homes and other structures during the summer of 2022.  Often when I see “weevil” cases it’ll be a handful of weevils indoors, but this year I’ve also seen plenty of reports of large numbers of weevils (hundreds or thousands!).  The top three species I’ve been seeing in Wisconsin have been the strawberry root weevil (Otiorhynchus ovatus), the imported longhorn weevil (Calomycterus setarius), and the black vine weevil (Otiorhynchus sulcatus).  There are a number of other species in this group that can invade structures as well.  Due to the similar appearance of these beetles, it’s often necessary to get a sample under the microscope to help confirm the exact species.  If you come across broad-nosed weevils in your home and want to know the exact type, feel free to send in a sample to the UW Insect Diagnostic Lab: insectlab.russell.wisc.edu/samples.

While these weevils can be a bit of a nuisance, there usually isn’t much of a need to spray (especially indoors).  In the grand scheme of things, good physical exclusion (i.e., sealing things up better with caulk, expanding insulation foam, better weatherstripping, etc.) can go a long way to help prevent broad-nosed weevils from getting indoors in the first place.  For the weevils that do make it indoors, insecticide really aren’t necessary and sweeping or vacuuming up these slow-moving pests is the best course of action.

Outdoor Insect Invaders

The Summer of Springtails

With the unusually dry weather we’ve had in Wisconsin this year, I would not have predicted that springtails (Collembola), would have been one of the commonest samples at the UW Insect Diagnostic Lab this summer. In general, springtails tend to thrive under damp conditions. These tiny (<1/10 inch long), insect-like creatures are commonly associated with leaf litter, rich soil, compost, and mulch or plant beds outdoors where they feed on fungi and decaying plant materials.

Photograph of a springtail on a log.
A tiny springtail on a decaying log outdoors—a common place to spot these creatures. Photo credit: Melissa McMasters via Wikipedia.

Springtails are ubiquitous and can be found around the globe under a wide variety of conditions. In many parts of North America, you can even bump into large numbers of dark-colored springtails (snow fleas) bouncing around on the snow in winter.  Springtails are a fairly diverse group with over 15 Families in North America, so there’s a lot of variability in terms of the color and overall appearance.

Indoors, it’s usually too dry for springtails to survive or reproduce unless damp conditions exist. Occasionally, they can be found indoors in association with overwatered houseplants, new construction (due to residual moisture in construction materials), plumbing leaks, and other moisture issues. In many cases, when springtails are spotted indoors, they originated outside and simply snuck in but perish shortly thereafter due to desiccation.

Chart shwoing drought conditions in Wisconsin in June of 2021.
Drought conditions in Wisconsin—June of 2021. Much of the state experienced drier than usual conditions this year, with some parts experiencing extreme drought conditions. Photo credit: US Drought Monitor Program: https://droughtmonitor.unl.edu.

With the lack of precipitation and this year, I haven’t gotten the impression that springtails are necessarily thriving outdoors. However, the hot and dry conditions are likely forcing springtails to sneak into structures or other spots that may be slightly damper, darker, and cooler. When they do make it inside, springtails are often spotted near moisture sources—kitchen or bathroom sinks, showers or bathtub drains, and basement floor drains. Some good news is that springtails are completely harmless to humans, pets and homes, and in most cases won’t survive long.

Hundreds of springtails along a home's foundations.
Hundreds of springtails along a home’s foundation. Photo submitted for a recent case at the diagnostic lab.

The following tips can be helpful when springtails are a problem indoors:

  • Monitor both indoors and outdoors—Visually inspect for areas with lots of springtails and see if potential entrance points into structures are nearby. Indoors, glue board traps from the hardware store or garden center can be helpful tools for monitoring and management.
  • Manage vegetation near the foundation of homes and other structures—Plants near a foundation can hold in moisture and create good habitat for springtails, spiders, millipedes, and insects that can wander indoors. Having a gap of 1-2 feet or more between a structure and plants increases airflow and can decrease humidity.
  • Avoid excessive mulch—A thick layer of mulch can hold in moisture and may create good habitat for springtails and other arthropods.
  • Physical exclusion—Sealing up potential entrance points into a structure can help with many pests, including springtails. Caulk and expanding insulation foam can be helpful in this regard. Inspect and replace weather stripping to make sure that windows and doors seal properly. Pay particular attention to high priority areas such as along the foundation, around window and door frames, and basement window wells.
  • Keep indoor humidity low—Running a dehumidifier and/or air conditioning can help decrease moisture and make it harder for springtails to survive. Repair or correct any drainage, plumbing, or moisture issues that may be increasing humidity levels within a structure. Allow houseplants to dry out between waterings; soil that is kept damp can be a potential hangout for springtails indoors.
  • Insecticides—Since springtails sneaking in from outside don’t survive long, spraying indoors is generally not warranted or helpful. If springtails are highly problematic, treating cracks and crevices on the exterior of a structure may decrease the number making it inside but won’t eliminate them outright.
Beetles, Big Bugs, Butterflies, IDL Highlights, In the News, Invasive Species, Ornamental Pest, Outdoor Insect Invaders, Uncommon Insects, Wasps and Bees

Hindsight: 2020 Trends at the Wisconsin Insect Diagnostic Lab

When the COVID situation reared its head back in March of 2020, I wasn’t sure how it would impact activities at the UW Insect Diagnostic Lab.  While there was a shift to handling diagnostics mostly remotely, in the end, 2020’s caseload of 2,533 ID requests was just shy of 2019’s all-time record of 2,542 cases.  

With Governor Evers’ Stay-at-Home Order last spring, our attentions were occupied by the unraveling pandemic and caseload at the UW Insect Diagnostic Lab was lighter than usual around that time.  However, as Wisconsinites shifted to working from home, it meant spending more time in yards and many Wisconsinites pulled out their green thumbs and established COVID “Victory Gardens”.  As a result, the diagnostic lab saw a record number of cases in July of 2020, with close to 600 ID requests that month alone. 

Monthly caseload at the UW Insect Diagnostic Lab in 2020. Credit: PJ Liesch, UW-Entomology.

Outreach activities of the lab saw a dramatic shift as well.  With in-person presentations and workshops off the table, virtual events afforded new opportunities—like a Japanese beetle seminar in July which drew nearly 900 participants. Regular events, like my appearances on WPR’s The Larry Meiller Show also continued through 2020, although I fielded calls from my home’s “reading nook” rather than the WPR studio.  

One of the biggest insect stories of 2020 was the Asian giant hornet.  Last May we learned that Asian giant hornets had survived the winter in the Pacific Northwest.  This of course led to a distinct increase of so-called “sightings” of that insect in Wisconsin, although every  “sighting” ended up being common insects from our area.  Last year, I saw dozens of ID requests for insects which ended up being look-alikes such as cicada killer wasps, pigeon horntails, and great golden digger wasps.  To date, the nearest sighting of the Asian giant hornet is well over 1,000 miles from us here in Wisconsin and poses no immediate threat to the upper Midwest.  Further reading: 6 Things to Know about the Asian Giant Hornet.

Some invasive pests had big years as well.  The viburnum leaf beetle, lily leaf beetle, purple carrot seed moth, and brown marmorated stink bug all increased their footholds in the state. Japanese beetle numbers varied a lot depending on where you were located in Wisconsin.  Some areas saw little pressure during droughty periods, while other parts of Wisconsin saw high Japanese beetle activity.  Gypsy moths had been quiet in Wisconsin for several years, but increased their numbers last year.  I saw a distinct increase of gypsy moth cases in 2020, and I’ll be keeping a close eye on that species in 2021.   

Come fall, we saw some stretches of unseasonably pleasant temperatures in October, November, and December.  During those periods, multicolored Asian lady beetles—which had been lurking in the background for several years—returned to the spotlight.  The multicolored Asian lady beetle activity around Wisconsin was some of the highest of the last decade.  Not to be left out of the fun, minute pirate bugs were abundant in some parts of the state and made warm, sunny fall days a little less pleasant due to their biting habits.  Speaking of biting insects, black flies were abundant in 2020 and made outdoor activities more challenging in June and July.  Mosquito activity varied around the state, although we did see a few cases of the Eastern Equine Encephalitis in 2020.

While we won’t see a big emergence of 17-year periodical cicadas in Wisconsin until 2024, small numbers of out-of-sync “stragglers” did emerge in southeastern Wisconsin last summer. 

A female Dryinid wasp. The forelegs are highly modified into scythe-like claws used to grasp other insects. Photo credit: Ty Londo.

No two years are the same at the UW Insect Diagnostic Lab and that includes some of the “X-Files” type cases as well.  Some of my favorite cases from 2020 include identifying phorid flies from dead radioactive cats (it’s a long story…), a grim-reaper-esque dryinid wasp, several massive black-witch moths from Central America, and a case involving a black widow spider found in a head of broccoli from the grocery store.  Never a dull moment at the UW Insect Diagnostic Lab!

—PJ Liesch
Director, UW Insect Diagnostic Lab

Biting Insects, Bugs, Galls, Outdoor Insect Invaders, Tree Insects

Hackberry Psyllids: Tiny, Jumping, Biting Insects

When it comes to insects that bite humans, there’s simply not a very long list of “common suspects”—especially during the cooler months.  Things such as bed bugs, fleas, and lice are all fairly straightforward to confirm.  However, I do occasionally bump into other creatures that can bite, such as bird mites, pirate bugs, and others. I also bump into cases where clients are experiencing biting or crawling sensations, but no insects of concern are found.  One of my tasks at the UW Insect Diagnostic Lab is to evaluate a situation to see if any of the less-common possibilities might be at play. If not, then I start to suspect delusory parasitosis (aka Ekbom’s Syndrome), which entomologists encounter on a fairly regular basis.  In one recent case, I was scratching my head for a while until I was able to confirm the presence of hackberry psyllids (Pachypsylla spp.)—tiny, jumping, biting insects that pop up under the right conditions.

A hackberry psyllid (Pachypsylla sp.). Several species in this genus cause galls on the leaves of hackberry trees. Photo credit: Katja Schulz, via Flick.

Hackberry psyllids (pronounced “sill-ids”) resemble miniature cicadas and are about 1/10th inch long. They have mottled grayish bodies and are sometimes called “jumping plant lice” or “hackberry nipple gall makers”. True to their name, these insects are associated with hackberry trees (Celtis occidentalis), which are commonly planted in the landscape as both yard and street trees.

In spring, overwintered psyllids lay eggs on emerging hackberry leaves. After the young psyllids emerge, their feeding causes unusual distortion of the leaf tissue, resulting in small “nipple-like” lumps (galls) on the leaves. Such galls are actually very common and most hackberry trees possess the characteristic galls to some extent. They may be alarming in appearance, but the galls are harmless to the trees and are essentially a minor “cosmetic” issue.   The young psyllids feed and develop within the protection of their leaf galls. Eventually, they complete their development and the next generation of adult psyllids emerges from the galls.

Galls on the underside of a hackberry leaf caused by psyllids from the genus Pachypsylla. Photo credit: Beatriz Moisset via Wikipedia

At this point, you might be wondering how these tiny plant-feeding insects end up bugging humans. Similar to boxelder bugs and Asian lady beetles, hackberry psyllids seek out sheltered overwintering spots in the fall and can easily invade homes and other structures.  With their tiny size, hackberry psyllids can be a bit harder to keep outdoors.  They are often overlooked and can easily squeeze through most window screens. Indoors, these insects face death by desiccation due to the dry conditions, but can be a nuisance as they jump or fly around. Occasionally, they’ll invade in fall and their activity resumes during warm spells over the course of a winter.

In addition to being a nuisance, hackberry psyllids can “bite”. These insects feed on plants (hackberry trees), but they do have a habit of “testing” various surfaces they land on to assess if another food source has been found. If they happen to land on exposed skin, they’ll use their slender, beak-like mouthparts to probe, which can feel like a small pinch. When they do this, hackberry psyllids don’t feed on blood or inject any kind of venom, but it certainly can be unpleasant.

The good news is that unless you have a hackberry tree in your yard or very close by, you probably won’t bump into appreciable numbers of these tiny insects.  If you do encounter them at your home, leaving windows closed on warm fall days (especially on south and west-facing sides of your house) or replacing window screens with a finer sized mesh can go a long way towards keeping them outside.

Beetles, Outdoor Insect Invaders, Phenology

Busy beetles: lady beetles take to the air and our homes

The spectacular fall weather this week has made it hard to work indoors. As Midwesterners, we know to appreciate the current warm spell as winter is just around the corner. If you’re like me, you’ve probably made it outside to take care of yard work, hike, grill out, or simply enjoy the fall colors. Speaking of colors, you’ve probably notices flashes of orange on the side of your home—multicolored Asian lady beetles (Harmonia axyridis). This fall, we’re seeing surprisingly high numbers of these lady beetles across Wisconsin.

An adult multicolored Asian lady beetle (Harmonia axyridis). Note the black “W” pattern just behind the head which helps identify this species. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

Just like us, the final warm days of autumn have worked these lady beetles into a frenzy of outdoor activity and our recent weather patterns are the key to this phenomenon. While not native to North America, the Asian lady beetle is an adaptable species and has a good feel for the seasons—it also knows that winter is coming. An important cue for lady beetle activity is the first frost or period of near-freezing temperatures in fall. This sets the stage and when the temperatures creep back up into the mid-60’s or 70’s, it initiates a massive game of hide-and-seek-shelter for these insects.

A group of overwintering Asian lady beetles beneath the loose bark of a dead tree. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

But why our homes? It turns out that Asian lady beetles don’t necessarily want to invade our homes—they simply look for sheltered spots to spend the winter. In more natural settings, I’ve found dozens of these beetles beneath the loose bark of dead trees or in firewood piles during the winter months.

In their native range of eastern Asia, multicolored Asian lady beetles are cliff dwellers. These beetles use visual cues to actively seek out conspicuous, exposed rock faces with cracks to squeeze into. They’re particularly fond of south or west facing cliffs, which get warmed by the sun in the afternoon when they’re most active. The lady beetles fly to these rock outcrops and examine the cracks and crevices to see if a suitable overwintering site has been found.  To us, our homes don’t necessarily resemble cliffs, but to the Asian lady beetles, the basic formula is there: large contrasting objects that stand out in the landscape with an abundance of vertical and horizontal lines resulting from modern design and construction methods. To the beetles, this looks close enough that they’ll fly to structures and wander around seeking out nooks and crannies to slip into as shown in the video clip below from the UW-Madison campus.

From the lady beetle’s point of view, these insects would really prefer to slip into a sheltered crack or crevice, hunker down for the winter, and leave again in the spring. However, when these insects get beneath siding or into a soffit area of our homes, they can accidentally pop out in the living quarters of the home—much to the dismay of the human inhabitants. This isn’t ideal for the insects either, which can face death by desiccation in the dry winter air indoors.

Enjoy these final warm days of autumn, because we’ll all be bundled up inside soon enough—with or without a bunch of lady beetles.

My final two cents: One of the best, long-term approaches to prevent nuisance issues with multicolored Asian lady beetles and other insects (like boxelder bugs and brown marmorated stink bugs) is to have good physical exclusion. This refers to making sure that potential entrance points on structures are sealed up due to good construction methods, caulk, expanding insulation foam, weatherstripping, or similar means.

Given their small general size, multicolored Asian lady beetles can squeeze through cracks or gaps as small as ⅛ inch in size. For perspective, this is about the same height as two pennies stacked atop one another. With that said, if you can easily slide two stacked pennies into a crack or crevice on the side of your house—it’s a big enough opening for multicolored Asian lady beetles to potentially get in!

 

Outdoor Insect Invaders, Outdoor Worms

A Wandering Horde of…Millipedes

It’s a dark, overcast night as the horde emerges from the nearby woods. There’s no real coordination, but thousands of them—perhaps tens or even hundreds of thousands—seem to wander aimlessly through the yard.  Some approach the darkened farmhouse and a few even manage to make it inside…

If this were and episode of The Walking Dead, the protagonists would be in a tough spot, but we’re not talking about zombies in this case.  Instead, the topic is millipedes, which have been surprisingly abundant this summer in parts of the Upper Midwest.

Greenhouse millipede.
Greenhouse Millipede (Oxidus gracilis). Photo Credit: Joseph Berger, Bugwood.org

Most everyone is familiar with millipedes.  They technically aren’t insects, but they are related as demonstrated by their segmented legs and “crunchy” exoskeleton (both are types of arthropods).  These multi-segmented, worm-like creatures can be common in damp areas and are perhaps most recognizable by their slow walk and their habit of curling into a spiral when disturbed.

Unlike the zombies portrayed in on TV, millipedes are really quite harmless.  Some millipede species have been documented as minor crop pests, but in the grand scheme of things, I mostly think of millipedes as being beneficial detritivores.  Millipedes feed on decaying plant materials and they return nutrients to the soil.  Their feeding also breaks down plant materials into smaller pieces, allowing microbes to more easily assist in the decomposition process.  Millipedes can be especially common in damp locations with abundant plant materials: compost piles, rich soil with high organic content, mulch beds, wooded or prairie areas, CRP land, lawns with a heavy thatch layer, and similar.

Millipede curled up in a spiral
A millipede curled up in a classic defensive posture to protect its legs. Photo credit: Joseph O’Brien, USDA Forest Service, Bugwood.org

While mostly beneficial, millipedes can occur in very high numbers under the right conditions and can be a nuisance when they seem to suddenly appear in yards and homes.  Hopkin and Read’s The Biology of Millipedes (1992) describes situations where massive millipede hordes have covered acre after acre of farmland or stopped trains, quite literally, in their tracks.  The Midwest does see large masses of millipedes on occasion and it was a particularly busy year at the UW Insect Diagnostic Lab for calls about these creatures.

The reasons behind millipede mass migrations aren’t fully understood, but moisture is often noted as a common factor.  Other potential reasons range from general weather patterns to habitat disruption, competition, and reproduction.  When millipedes do move about, many species shun the sun and prefer to move at night or during very overcast days.  When they encounter a building, millipedes can sneak inside, although this is really accidental—it’s too dry for them to survive indoors and they typically die within a day or two.

Millipedes on a home's foundation
Thousands of millipedes along a resident’s home. From a case submitted to the UW Insect Diagnostic Lab this summer.

Millipedes can be frustrating when mass migrations occur as there’s not much that can be done to completely stop them.  It’s not uncommon to have cases where hundreds or thousands of of millipedes crawl onto the foundation or siding of a home every night.  If they mostly stay outside, that’s one thing, but this summer I’ve had multiple cases where large numbers of millipedes (hundreds) had snuck under a building’s siding and then rained down through ceiling light fixtures.  This sounds like something out of a sci-fi film, but if you were trying to sell your home it could be a real-life nightmare scenario.  In such cases, there simply isn’t any way to make the millipedes magically disappear.  Insecticides may be tempting but only help to a certain extent because more millipedes can simply show up the next day.

If you’re staring down a millipede horde, one of the most important approaches is physical exclusion.  Inspecting the exterior of a home and physically sealing up cracks, crevices, and other potential entrance points with caulk, expanding foam, or new weather stripping can be a chemical free, long-term solution to at least keep millipedes outdoors.  Because millipedes prefer damp areas with decaying plant material, keeping landscape pants, fallen leaves, and thick layers of mulch away from the foundation of a home could also help reduce hiding areas for millipedes.

Luckily, millipede mass migrations eventually run their course and quiet down on their own.   This year, I saw a spike in millipede reports starting in mid-June and running into early August before subsiding.

Ants, Indoor/Kitchen Insects, Outdoor Insect Invaders

Identifying Insects by Smell, Part 2: Odorous House Ants

When it comes to ants at the UW Insect Diagnostic Lab, the top species seen at the lab include carpenter ants (Camponotus spp.), pavement ants (Tetramorium immigrans), and odorous house ants (Tapinoma sessile).  Odorous house ants were the most commonly reported ants at the lab in 2018, possibly due to the rainy conditions which can force these ants indoors in their search for food.

Odorous House Ant. The single flattened node is hidden under the gaster. Photo credit: April Nobile, specimen: CASENT0005329, from www.antweb.org.

Identifying ants by sight and smell
The tiny brownish odorous house ant measures in at only an eighth of an inch long, but a few features allow for quick identification.  Ants are generally broken into two main groups depending on the numbers of bumps or “nodes” in their constricted waist.  Odorous house ants are considered “one node” ants, although their single node is flattened and is hidden from view by the gaster (sometimes mistakenly referred to as the “abdomen” of ants).  This is strikingly different than other ants, such as carpenter ants or field ants, where the single upright node can even be visible to the naked eye.  This flattened node of odorous house ants is a key identifying feature but does require magnification to interpret this trait.

Carpenter ant—note the visible node or “bump” in the narrow waist. Photo Credit: Judy Gallagher, via Wikipedia.

Interestingly, the easiest way to identify these ants isn’t by sight, but by smell.  Identifying insects by smell may sound odd, but can be a quick and dirty way to confirm the identity of this ant species, and a few other ants like citronella ants.  When squished, odorous house ants have an odor reminiscent of coconut, although some say rotting coconut or even blue cheese.  This scent fades with older, dried-out specimens but is usually quite noticeable in fresh ants.

Country ant, city ant:
Odorous house ant colonies occur both indoors and outdoors in the Midwest, but the overall location of these ants in the landscape can have a drastic influence on colony structure and behavior.  In natural areas (such as forests), odorous house ant colonies tend to be small (often <100 workers) and the ants are generally “well behaved”.  In urban areas, these ants can produce much larger populations with multiple queens, tens of thousands of workers and many different nesting sites. They can behave like an invasive species in such situations.

When it comes to their nesting habits, odorous house ants don’t produce mounds like other common ants.  Instead, these ants are fond of preexisting cavities—small hollow voids beneath rocks or man-made objects, amongst log piles, fallen leaves, mulch beds, or similar spots.  I’ve even seen them take advantage of the cozy space inside of a fake rock “Hide-a-Key” on several occasions!  Indoors, odorous house ants like to nest in hollow cavities such as wall voids, especially if a moisture source is nearby.  These ants can also easily wander indoors when foraging, making them a common indoor nuisance invader.

SMall black ant—an odorous house ant worker
Odorous House Ant (Tapinoma sessile) worker. Photo Credit: JJ Harrison via Wikipedia

Got dessert?
In addition to their essence-of-coconut scent, odorous house ants are also known for having a notorious sweet tooth.  Ant species vary quite a bit in their food preferences, with certain ants seeming to favor the “keto diet” with a strong preference for proteins or fats.  In contrast, odorous house ants have a particular fondness for carbohydrate-rich materials, such as honeydew from aphids, nectar from plants, or sugary human foods.  As a result, these ants routinely invite themselves to picnics and into kitchens.  However, their sugar-loving ways can also be their Kryptonite and odorous house ants usually respond well to sugar-based baits when they do find their way indoors.

Beetles, Borers, In the News, Invasive Species, Outdoor Insect Invaders, Phenology, Ticks

Spring’s Coming…and so are the Insects

With daylight saving time beginning over the weekend and warmer temperatures knocking at our door, spring is finally crawling our way.  Last winter is one we won’t soon forget—the season started out mild before temperatures plummeted with January’s polar vortex.  During the coldest stretch, our coping strategy might have involved layers of blankets and reruns on Netflix, but what about the bugs? Questions regarding the winter impacts on insects have been some of the commonest at the UW Insect Diagnostic Lab this year.  There will undoubtedly be some impacts of this year’s polar vortex, although many insect species are well-equipped to deal with the cold.  Before we know it, overwintering insects will become active again in the Midwest and many species will simply shrug off the polar vortex as if it hadn’t happened.  For insects that didn’t fare as well in the cold, high reproductive capacities will likely allow their numbers to bounce back relatively quickly.

Thus, 2019 isn’t going to be insect-free by any means and intuitively this makes sense.  We know that every year insects make it through the winter months and become active as temperatures creep up in spring.  Looking at an evolutionary time scale, this year’s cold snap wasn’t the first time that the species in our area have encountered frigid temperatures before, and many creatures are adapted to survive surprisingly cold conditions.   We might have chosen to block it out of memory, but the Midwest experienced a very similar situation a mere five years ago.  Weather patterns in January of 2014 saw temperatures dip to -20˚F and colder in some spots of the Midwest.  The following summer, we still had plenty of insect activity in the region.

Thermometer from a cold and crisp Wisconsin morning. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

Since we don’t see insects bundling up with tiny mittens and scarves, how do they make it through the winter?  It turns out that insects and other arthropods have a number of strategies to help them survive.  For starters, insects typically have a particular life stage (e.g., egg or pupa) that is more tolerant of adverse environmental conditions, such as freezing or desiccation.  Passing through the winter as a more resilient life stage is a good starting point.

Some of the other strategies are surprisingly similar to humans.  Just like snowbirds heading to warmer states for the winter, certain insects like monarch butterflies and green darner dragonflies migrate southward to avoid the coldest temperatures.  Our official state insect (the honey bee) doesn’t migrate, and instead chooses to remain active.  Honey bee colonies shiver together as an insect version of central heating to keep the inside of their hive a constant temperature.  Other insects simply seek shelter and overwinter in protected locations to avoid the worst of the cold.  Insects like the multicolored Asian lady beetle, boxelder bugs, and the invasive brown marmorated stink bug are fond of sneaking into man-made structures to spend the winter.  If insulation and central heating make homes warm enough for us, it’s plenty warm to prevent insects from freezing.  In more natural settings, such insects might end up sheltering in rock piles or beneath the loose bark of a dead tree.  Those locations might not be as toasty as a house, but they can still provide adequate respite from the cold—meaning that insects using this strategy should have been well protected from this year’s cold spell.  Similarly, many insects and other arthropods spend the winter below ground or on the surface of the ground amongst a layer of insulating leaf litter.  In addition, many parts of Wisconsin had a solid covering of snow by the time the polar vortex arrived, so creatures such as ticks had a thick layer of insulation from the coldest of the cold.

Another strategy utilized by insects is the production of natural antifreeze compounds (specific alcohols or proteins) which serve as cryoprotectants to help prevent freezing within their bodies.  We know that a cup of water will turn to ice at 32˚F, but dissolve salts or other substances in that same water and it will require colder temperatures to freeze it.  Insects producing high concentrations of these cryoprotectants can remains unfrozen at surprisingly low temperatures, similar to a bottle of high-proof spirits kept in a freezer.  Taking it even further, the common black and brown woolly bear caterpillars seem to embrace the cold and actually allow ice to gradually form within their bodies.  This may sound like a fatal mistake, but by regulating the formation of ice crystals on their own terms, woolly bear caterpillars are able to control where ice formation occurs and limit it to specific areas of their bodies to prevent damage.  If the same caterpillars were unprepared and froze rapidly, their cells might burst like a can of soda put into a freezer.

The ubiquitous woolly bear caterpillar (Pyrrharctia isabella) is well adapted to winter conditions. Photo credit: Dave Govoni via Flickr.

And then the ash borer…
The insect I’ve gotten the most questions about lately has been the emerald ash borer.  While not native to our area, this invasive pest comes from similar latitudes of eastern Asia and the cold-hardy larvae are fortified with cryoprotectants as they spend the winter beneath the bark of ash trees.  These natural antifreeze compounds have their limitations though, and just like sidewalk salt failing to melt ice on a really cold day, the cryoprotectants only work down to certain temperatures before freezing (and death) occurs.  For emerald ash borer, the point at which freezing spontaneously begins to occur (the supercooling point) is when temperatures dip into the range of -13˚F to -23˚F.  This year’s polar vortex did see temperatures fall into and below that range, which would have killed plenty of emerald ash borer larvae, although the insulating effects of the tree bark likely provided some buffering.

The pale end of a surviving emerald ash borer larva sticking out from its tunnel. When larvae are killed by freezing, they typically become discolored. This sample came from the Milwaukee area in early March, 2019. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

Emerald ash borer populations will almost certainly take a hit from this year’s polar vortex, but it’s not going to be a knockout blow.  Give it some time and the reproductive capacity of this invasive species will allow populations to rebound.  The news reports of cold-induced EAB mortality in early February might have been encouraging, but scientific models from the US Forest Service suggest that to really knock down EAB in the long run, we’d have to experience arctic blasts on a regular basis—news that many Midwesterners aren’t likely to receive warmly.

Further Reading: For a great read on how wildlife survive the winter, check out Bernd Heinrich’s Winter World