All posts by pliesch

Brood X Cicadas in the Midwest?

Will we see Brood X cicadas in Wisconsin or the upper Midwest this year? Read on to find out:

Cicadas—they’re all over the news and soon to be out by the billions. All this buzz is about periodical cicadas, a group of species from the genus Magicicada which emerge once every 17 years (or every 13 years in some cases). Periodical cicadas are only found in the eastern United States and vary by location and the timing of their activity. To help categorize these insects, entomologists refer to each cohort of cicadas as a “brood” and have numbered them with Roman numerals. This year’s cicadas are referred to as Brood X (i.e., Brood ten) and last emerged in 2004.

Two periodical cicadas on a rock
Brood XIII periodical cicadas in Lake Forest, IL in June of 2007. Photo Credit: Janet and Phil via Flickr (CC).

Periodical cicadas are amongst the longest lived insects and their long life span and massive emergences are believed to be a survival strategy—by overwhelming predators with sheer numbers, they simply can’t all be eaten. But the wait for their appearance is a long one.  Periodical cicadas spend 17 years below ground as juveniles (nymphs) feeding on the sap from tree roots, before making their way above ground. Their emergence is associated with soil temperatures, and when the soil has warmed to 64˚F, they emerge. This corresponds to parts of April, May, or June depending on the location on the map.

Once they make their way above ground, the cicadas molt and transform into adults.  Shortly thereafter, a raucous mating free-for-all commences. After mating, the females cut small slits into twigs of trees to deposit their eggs. The eggs hatch and the juveniles head to the soil for their lengthy development. Periodical cicadas don’t live long as adults (a matter of weeks), so it’s a long build up to a noisy grand finale.

Ground covered by periodical cicadas
Ground covered by periodical cicadas. When these insects emerge, it can be by the billions! Photo credit: James St. John, via Wikipedia (CC).

With all the attention in the news, many Wisconsinites and other Midwesterners are wondering if they’ll be able to see or hear Brood X cicadas in their area this year. For Wisconsin, Minnesota, Iowa, and most of Michigan and Illinois the answer is noalthough they aren’t terribly far away either. Brood X cicadas can be found in over a dozen eastern states, but primarily emerge in three main pockets:

  1. Indiana, Ohio and nearby slivers of eastern Illinois and southern Michigan
  2. Southern Pennsylvania and parts of nearby Delaware, Maryland, Virginia, New Jersey, and New York
  3. Eastern Tennessee and nearby parts of North Carolina and Georgia

Periodical Cicada Brood Map from US Forest Service

Map of active periodical cicada broods of the United States. Map credit: USDA Forest Service. Click map for full size version and additional information.While we won’t see Brood X cicadas here in Wisconsin, we will see other periodical cicadas in the not so distant future. Wisconsin is home to Brood XIII cicadas, which last emerged in 2007, meaning that the next big emergence in the Badger State is only a few years off in 2024. In the meantime, we’ll still see and hear plenty of our typical “dog day” cicadas during the warm days of summer.  To learn more about Brood XIII cicadas in Wisconsin, check out this post from last year.

The Monarch’s Precarious Position

Endangered. It’s an imposing term and not one to be taken lightly. Monarchs have been in a perilous spot for years and there have been rumblings of potentially listing monarch butterflies (Danaus plexippus) as endangered by the UW Fish & Wildlife Service. After delays, we finally received a decision in December of 2020—“warranted but precluded”.

Monarch butterfly on the UW-Madison Campus. Photo Credit: PJ Liesch, UW Entomology.

In a technical sense, labeling a species as endangered isn’t as simple as merely placing it on a list. There’s a lengthy review process and potential species are evaluated in terms of how pressing their situation is. In the case of monarchs, the “warranted” part of the decision indicates that monarchs are indeed in need of protection. The alarming part is the “but precluded” statement—it essentially means that other species are facing even more pressing situations and are ahead in line. Some consider us to be in the midst of the “sixth” major extinction event on planet earth, although this one differs in that it’s caused by humans. In short, there are a lot of species that will be facing declines and extinction. At the time of the monarch’s decision from US FWS, there were currently 161 other species listed ahead of monarchs in the priority queue.

Unfortunately, since the US FWS decision last December, we’ve had some alarming news come out about monarch populations. First, it’s helpful to understand monarchs in the US as we actually have two main populations: a western population and an eastern population.

The western population can be found in states such as California, Oregon, Washington, Idaho, Nevada, and Utah west of the Rocky Mountains (a natural barrier to dispersal). While we may think of monarchs migrating to the area outside of Mexico City, this western population heads from their summer grounds to overwinter in parts of southern California. Unfortunately in January of 2021, the Xerces Society reported that only 1,914 total overwintering monarch butterflies were counted—a 99.9% decrease over the last 30 years. For comparison, a similar assessment conducted  in 1997 estimated over 1.2 million overwintering monarchs. Experts have estimated a critical “extinction threshold” of 30,000 monarchs for this western population to hang on. With fewer than 2,000 monarchs spotted in late 2020, the western monarch’s situation can’t get any more urgent.

In the Midwest, we see the eastern monarch population which ranges over much of eastern North America east of the Rocky Mountains. These are the monarchs that make the long perilous flight to overwinter in the mountains outside of Mexico City. While the eastern monarch population’s situation isn’t necessarily as dire as out west, it’s still tenuous to say the least. An assessment of the eastern population is usually released in late winter and the most recent estimate found a 26% drop in overwintering monarch populations compared to last year. Over the last 20 years, the eastern monarch population has declined by approximately 90%. With larger numbers of butterflies in the eastern population, scientists don’t count individual butterflies to gauge their numbers. Instead they estimate the area occupied by densely-packed overwintering monarchs clustered together by the thousands on pine trees at their overwintering habitat in Mexico. The recent assessment found monarchs packed into an area of 2.1 hectares (5.2 acres). While this may sound like a big area packed to the gills with butterflies, it’s estimated that 6 hectares (14.8 acres) of overwintering monarchs is a “critical mass” needed to maintain the eastern population. Unfortunately, the news of both the eastern and western monarch populations comes as a punch to the gut since their numbers have been trending downwards over time.

Assessment of overwintering monarch butterflies, released 2021. Source: MonarchWatch.  Click for more detail.

While monarchs may be in a tight spot, they aren’t gone yet. With the “warranted but precluded” finding, the US Fish & Wildlife Service now considers monarchs a “candidate” species for listing and will continue to assess the situation as higher priority species are added to the endangered species list. In the meantime, if you’re looking for ways to help monarchs, the Wisconsin Monarch Collaborative was created in 2018 to coordinate conservation efforts of this species in our state—check out their website to see what you can do to help the monarchs: https://wiatri.net/Projects/Monarchs/.

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

Fungus Gnats: Tiny Flies Around Your Houseplants

With winter’s arrival, the caseload at the UW Insect Diagnostic Lab is low, although ID requests continue to trickle in. Recently, dark-winged fungus gnats (Family Sciaridae) are one of the commonest insects I’ve seen at the lab. These tiny (1/16 – 1/8 inch long), dark-colored flies are almost always associated with houseplants.

Adult fungus gnat showing the distinctive, curved “Y” fork in the wings.  Photo Credit: B. Schoenmakers, via Wikipedia.

Despite their small size, adult fungus gnats can readily be identified by their wing venation. Using a bit of magnification, the translucent wings of these insects possess an oblong, rounded “Y” towards the tips of the wings. While the delicate adults gnats may catch our attention, the larvae are at the root of the problem. The slender, worm-like larvae possess a dark head capsule and live in moist environments.

The connection with houseplants has to do with the feeding habits of the larvae. Fungus gnat larvae generally aren’t plant pests, but scavenge on fungal spores. If the soil of a houseplant is kept too moist, it can create ideal conditions for them. An abundance of fallen decaying plant materials (leaves, etc.) on the soil surface can also contribute. Some of the commonest sources of fungus gnats (and other houseplant pests) are “outdoor” plants which were brought indoors in the fall.

Adult fungus gnats may be a nuisance, but are harmless and short-lived. They will often be observed near potted houseplants (where females can lay eggs) or at nearby windows. When it comes to fungus gnat problems, the following approaches can be helpful:

Sticky card traps can be a useful non-chemical approach for monitoring fungus gnat populations over time and capturing adults. Photo credit: PJ Liesch, UW Entomology.

1) Dry out the Soil: Fungus gnat larvae thrive in damp soil or potting mix. Cutting back on waterings is often the single most important step in dealing with fungus gnats and the mere presence of these gnats is often an indicator of overwatering. Allowing the soil to dry out between waterings decreases survival of the larvae. For succulents and other popular plants that are tolerant of dry conditions, cutting back on waterings can often correct a fungus gnat issue over time without any additional steps.

2) Sticky Card Traps: These traps look like bright yellow index cards, but are covered with a sticky adhesive. When purchased at local hardware stores, garden centers, or online, they usually include small stakes to help place these cards into pots. The adult fungus gnats are attracted to the color of the traps and can become stuck in the adhesive. Used alone, these traps will not eliminate fungus gnats. However, these traps are a non-chemical way to capture adults and can help when used in combination with other approaches. If you have significant fungus gnat numbers, swapping out sticky cards on a regular basis can help monitor for trends over time.

3) Soil Monitoring: If you have lots of houseplants, determining which plant(s) is/are harboring the larvae can be a challenge. One helpful approach is to place slices of potato on the soil surface of potted plants. If larvae are present in a given pot, some may come to the surface to feed on the readily-available starches of the potato. Checking the potato slices for the presence of the dark-headed larvae can help determine where to focus your attention.

4) Cultural Practices: If fungus gnats are really bad, it can sometimes make sense to discard a problematic plant to prevent it from serving as a continual source of fungus gnats. Alternatively, a favorite plant could be washed to bare roots and re-potted in fresh potting mix. When obtaining new plants, it can be helpful to isolate and monitor new plants for fungus gnat or other insect activity before placement amongst other houseplants.

5) Soil Treatments: With severe or persistent infestations of fungus gnats or in cases where watering can’t be reduced, treating the soil is an option to directly target the larvae. The commonest option is to use a product labelled for use on houseplants containing Bacillus thuringiensis israelensis (Bti). These products are based on a naturally-occurring bacteria that is toxic to fly larvae. Such products can be applied as a liquid drench (e.g., Gnatrol) or as granules (e.g., Mosquito Bits) to the soil surface and watered in. Such products won’t eliminate fungus gnats overnight, but can be effective over the course of several weeks.

6) Sprays for Adult Fungus Gnats: Spraying for adult fungus gnats with is not generally effective or recommended.  Targeting the adults will only provide temporary relief and it is much more effective in the long-run to target the larvae at the heart of the problem.

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.

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!

 

Riding the Wind: Storms Transport Rare Moths to Midwest

The largest moths you’ll likely encounter in the northern United States are the giant silk moths (Family Saturniidae).  We have a handful of species in the Upper Midwest which can be encountered with some regularity during the summer months: cecropia moths, polyphemus moths, luna moths, promethea moths, and imperial moths.  True to their name, the giant silk moths don’t skimp on size—they generally have wingspans in the range of 3 – 6 inches, depending on the species.  These moths are native to our area and the impressively large caterpillars feed on the leaves of various hardwood trees.

An adult polyphemus moth (Antheraea polyphemus) resting on a tree trunk in northern Wisconsin. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

Finding an adult giant silk moth or one of the caterpillars is always a special occasion.  However, there’s an even more impressive large moth, which occasionally pops up in our area—the Black Witch (Ascalapha odorata).  The black witch has a wingspan of around 6 inches and can often be mistaken for a bat due to its dark colour.  This tropical species doesn’t natively occur in our area and originates in parts of South America and Central America.  However, the adult moths are somewhat regular “strays” and find their way as far north as parts of Canada.  Still, black witches aren’t common in Wisconsin (or the US in general), and I typically only hear of a few reports in the state each year.

An impressive cecropia moth caterpillar (Hyalophora cecropia). Photo Credit: Judy Gallagher via Wikipedia.

Wind plays an important role in the movement of black witches from their native habitat.  One report even documented an adult black witch traveling with a strong westerly wind to an island in the south Atlantic—a distance of over 2,000 miles from South America.  In the upper Midwest, dips in the jet stream and storm systems can play an important role.  Since starting at the UW Insect Diagnostic Lab in 2014, I’ve seen several cases where black witches are spotted in late summer after hurricanes have hit the Gulf Coast states.  Along these lines, hundreds of black witch moths arrived in Texas as Hurricane Claudette passed through in 2003.  Following such an intense journey, the moths are often damaged, with tattered wings or other injuries.  Surprisingly, some moths seem to arrive in nearly pristine condition, like this beautiful specimen spotted in Door County last month shortly after hurricane Sally made landfall.

An adult female black witch (Ascalapha odorata) moth, which was spotted in a warehouse in Door County, Wisconsin in September of 2020. The moth is in surprisingly good condition for having been transported several thousand miles in a short period of time. Credit: photo submitted to the UW Insect Diagnostic Lab.

If you do ever spot a black witch, consider yourself lucky.  If you’re extremely lucky, you might even spot one of the rarest moths that strays to the Midwest—the “owl moth” (Thysania zenobia)—another large moth which has only ever been spotted in Wisconsin a few times and is much rarer than the elusive black witch.

Great Golden Digger Wasp: Another Asian Giant Hornet Look-Alike

With the media craze about “murder hornets” this past spring, I’ve seen a definite increase in reports of Asian giant hornet look-alikes at the UW Insect Diagnostic Lab this summer.  Many folks recognize the commonest look-alike in the Midwest, the eastern cicada killer (Sphecius speciosus), which becomes active in July around the time that their prey (cicadas) start emerging.  Another look-alike is one that you might not have bumped into before—the great golden digger wasp (Sphex ichneumoneus).  Similar to Asian giant hornets, great golden digger wasps are large and nest in the ground, which are reasons why they may be mistaken for the former.

If you haven’t spotted one before, great golden digger wasps can be a bit intimidating in appearance as they can easily be over an inch long.  However, their anatomy and appearance are quite different compared to Asian giant hornets.  Great golden digger wasps are mostly black with a rusty-reddish color at the base of the gaster (“abdomen”).  Their legs are the same reddish color and the black thorax and head possess fine golden setae or “hairs” (hence “golden” in their name).  In contrast, Asian giant hornets have distinctive black and yellow stripes on their gaster and a vibrant yellowish-orange head.  Great golden digger wasps belong to the “thread-waisted” wasp family (Family Sphecidae) and have a long, slender petiole (“waist”).  This isn’t as thin and narrow as the “waist” of the related black and yellow mud dauber (Sceliphron caementarium), but still is quite noticeable when viewed from the side.

Great golden digger wasp
Great golden digger wasp (Sphex ichneumoneus); note the slender petiole or “waist”. Photo credit: Judy Gallagher, via Wikipedia.

In terms of their biology, both Asian giant hornets and great golden digger wasps do nest in the ground, but the similarities end there.  The Asian giant hornet is really quite similar to our ground-nesting yellowjackets in terms of their nesting behavior.  These are social creatures which start nests from scratch in spring and build up in size over the course of the warmer months.  Colonies ultimately die out in fall except for the “new” queens which overwinter.  With a large colony of relatives to defend, social wasps can be defensive, especially when colonies are at peak size.

In contrast, great golden digger wasps are solitary ground nesters.  Without a large colony of relatives to defend, they’re usually non-aggressive and very unlikely to sting.  Stings are only likely if one were to pick one up bare-handed—in which case you might be asking for it!  Similar to cicada killer wasps, each female great golden digger wasps excavates small tunnels in sandy soil and provisions them with prey for their young to feed on.  In the case of the great golden digger wasp, prey consists of katydids, crickets, and relatives from the “grasshopper” group (Order Orthoptera).  Rather than kill outright, the females inject their prey with a paralytic “cocktail” to keep them alive and fresh for their young to feed on—what a way to go!  In addition to hunting katydids, adult great golden digger wasps visit flowers and can be beneficial pollinators.

Great golden digger wasp on flower
Great golden digger wasp (Sphex ichneumoneus) drinking nectar from a flower. Photo credit: Roy Niswanger, via Flickr.

Because they’re unlikely to sting humans, controlling great golden digger wasps is rarely justified and these magnificent creatures can simply be admired.  Ultimately, these wasps are strongly associated with sandy soil, so if you see them in your yard every year and would prefer to not have them around, modifying the landscaping may be a long-term option to dissuade them from an area.


Author’s note: As of August 2020, Asian giant hornets have not been found in Wisconsin or anywhere in the Midwest.  In North America, these insects are only known from far northwestern Washington state and nearby parts of British Columbia. 

See this earlier post for additional details on the Asian giant hornet.

Some Insects Don’t Understand Social Distancing

In the grand scheme of things, most insects (and spiders) are loners.  Perhaps they set a good example for us in 2020 with their social distancing.

Of course, insects have to find a mate to reproduce at some point in their lives*, but out of the 1 million+ described insect species, being truly “social” isn’t the norm.  There certainly are some well-known examples of insects that are eusociali.e., they live together as a colony.  Examples include ants, certain types of wasps (such as yellowjackets and paper wasps), some bees, termites, and a few other interesting examples.  However, there are many insects that are much more solitary in their habits.  If you think of our bees in the Great Lakes region, we have roughly 500 species.  Other than honey bees, bumble bees and a few others, the vast majority of these species are solitary creatures with each female doing her own thing.

Two herds of Cerastipsocus venosus barklice. Photo submitted to UW Insect Diagnostic Lab.

Interestingly, there’s a quirky insect that can be commonly encountered this time of the year and it missed the memo on social distancing.  I’m referring to an interesting species of barklouse (Order Psocodea): Cerastipsocus venosusBarklice are relatives of true lice (e.g., head lice and pubic lice) but they’re really quite harmless to humans and tend to be scavengers.  Barklice make up an obscure group of insects and many entomology students simply identify them to “order” level as this group can be challenging to narrow down further to family, genus, or species.

Group of Cerastipsocus venosus juveniles. Note the striped abdomens which make them easy to identify. Photo submitted to UW Insect Diagnostic Lab.iny

If you haven’t encountered Cerastipsocus venosus (aka “tree cattle”) before, it might catch you off guard to find a group (formally known as a “herd”) of these small insects hanging out together on the bark of a tree or a rock in your yard.  The tiny juveniles are particularly striking with yellow stripes on their abdomens.  The adults are larger (up to 1/4″ long) and possess black wings.

A Cerastipsocus venosus adult. Note the black wings, which are only found in the adults. Photo submitted to UW Insect Diagnostic Lab.

Rest assured, these barklice pose no threat to trees or other plants in our yard and these native insects simply nibble on lichens, and pieces of dead tree bark.  Every year I get many reports of these insects in mid- and late- summer at the UW Insect Diagnostic Lab and there’s no need to spray or do anything about these if you spot them in your yard.  These barklice don’t seem to stay in the same place for very long, so perhaps their herds just move along looking for greener pastures.


*Some insects are able to reproduce asexually, and don’t technically have to find a mate…

Cicada Mania in Wisconsin?…Not ‘Til 2024

Perhaps you’ve heard some buzz about periodical cicadas (Magicicada spp.) lately. These insects resemble our typical “dog day” cicadas, which we see in mid-to-late summer in Wisconsin, but they are orange and black with vibrant reddish eyes instead of a dull greenish color. Parts of the US are currently seeing mass emergences of periodical cicadas, which appear by the millions every 13 or 17 years depending on the species. I’ve had a number of questions this last month asking if this was “the year” for us to see them in Wisconsin, but it’s not time for the big show…yet.

Left: A common “dog day” cicada; photo credit: PJ Liesch, UW Insect Diagnostic Lab. Right: A peridoical cicada; photo credit: Jay Sturner, via Wikipedia

Periodical cicadas are sorted into cohorts known as “broods”, which occur in particular geographic areas and emerge at specific points in time. For the most part, these insects are excellent timekeepers and some broods have been documented as far back as the 1600’s in the eastern US. There are entire websites and apps dedicated to these insects and their schedules, and scientists have labelled broods with Roman numerals to help differentiate the cohorts.

Map of active periodical cicada broods of the United States. Map credit: USDA Forest Service. Click map for full size version and additional information.

With all the broods out there, some parts of the US do see these cohorts overlap in space, but these can be separated by the years in which they emerge.  In Wisconsin, the situation is fairly straightforward as we only see a single brood: Brood XIII. Brood XIII’s 17-year cicadas last emerged in 2007, meaning that we’ve got four more years to wait until their mass emergence in 2024.

Interestingly, I’ve received a number of photos and reports of periodical cicadas in Wisconsin over the last month or so. I’ve had several confirmed reports from the Lake Geneva area (Walworth County) a confirmed report from southeastern Dane County, and a suspected report from Sauk County.  While most periodical cicadas stick to the schedule, occasionally some of these insects veer off course. These out-of-sync individuals are referred to as “stragglers” and it turns out that Brood XIII has a history of these stragglers. In the late 1960’s, large numbers of stragglers were documented in the Chicago area. Likewise, many of the Chicago suburbs are seeing a similar phenomenon this year. With that said, we did technically see some periodical cicadas this year, but we’ll have to wait a few more years before the real “fireworks”.