Category Archives: Outdoor Worms

A Wood-Boring Insect Mystery

Imagine it’s August and as you wander in from your backyard, you notice a small pile of sawdust at the bottom of the door frame.  It might not be much sawdust, but you also find a few holes in the wood trim nearby.  It definitely seems to be insect damage, but who’s the culprit?

Unexpected insect damage to wood trim.

If you came up with a list of insects in the upper Midwest that can damage the wood of your home, it wouldn’t be terribly long.  For good reason, termites might be the first insect to come to mind, although our eastern subterranean termites are restricted to isolated pockets and are not commonly encountered in Wisconsin.  A close second on the list might be carpenter ants.  Interestingly, carpenter ants don’t technically eat (e.g., digest) wood and merely excavate soft, rotting wood to create a nesting site.  If anything, their presence in a home might be an indicator of a water damage.  Powderpost beetles can also attack wood and are commonly encountered in old barn beams and log cabins.  Carpenter bees help round out a list of the “usual suspects”.  These wood-boring bees can create good sized holes (a half inch across), although with their preference for unpainted softwoods used for trim, siding, and fence posts, their damage is mostly cosmetic in nature. 

Then another clue comes to mind—the nearby shrubs that had been eaten by some kind of worm-like insect over the past few weeks. 

Larva of a dogwood sawfly showing the whitish, waxy coating. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

When it comes to wood-damaging pests, sawflies generally don’t come to mind.  Sawfly larvae—Mother Nature’s caterpillar copycats—tend to feed on plant leaves.  Species like the European pine sawfly, dusky birch sawfly, rose slug sawfly, Columbine sawfly, pearslug sawfly, and birch leafminer sawfly can all be commonly encountered feeding on plants during the growing season.  One species that was common in 2018—the dogwood sawfly—is unique in that it not only causes plant damage but can also damage wood trim and siding of homes.  The dogwood sawfly is one of our commonest pests of native and landscape dogwoods (Cornus spp.).  When larvae are small,  they have a whitish waxy coating thought to mimic bird droppings and they can often be found curled up on the undersides of dogwood leaves.  As larvae mature, they lose the waxy coating and their black and yellow coloration becomes conspicuous.   

Mature dogwood sawfly larva with classic black and yellow appearance.

So how does this plant-feeding species end up damaging wood?  As is the case with any insect that undergoes complete metamorphosis, the larvae need to pass through the pupal stage to make it to adulthood. Insect pupae, however, are generally immobile can make an an easy meal for any predator that stumbles upon them.  Thus, many insects seek out tucked away spots to complete their pupal stage.  When ready to pupate, dogwood sawfly larvae typically create their own hideaway by chewing small chambers in rotting wood such as twigs, branches, or logs near the shrub they had been feeding on. 

Small chambers chewed into a fallen twig—a “typical” spot for dogwood sawfly to pupate.

If rotting wood is unavailable, the larvae may turn to other nearby wood materials—including wood trim and siding.  This typically occurs when larvae had been feeding on ornamental dogwood shrubs planted close to a home.  In the grand scheme of things, these insects don’t cause that much damage to wood, although homeowners won’t be thrilled if they’ve been caught off guard by this unexpected wood-damaging pest! 

Sphinx Moths—Hovering at a Flower Near You

If you’ve watched the flowers in your yard or local park recently, you might have noticed some surprising visitors hovering at the flowers—the hummingbird-like sphinx moths.  Several species in the “sphinx” or “hawk” moth group (Family Sphingidae) are known for their day-flying, hummingbird-like behavior.  From a distance these moths can easily be mistaken for hummingbirds as they skillfully maneuver from flower-to-flower sipping nectar with their long mouthparts.

One of the commonest members of this group in Wisconsin is the white lined sphinx moth (Hyles lineata).  With a wingspan of nearly 4 inches, it’s easy to understand why this species can be mistaken for a hummingbird as it feeds.  The greyish adults are easy to pick out and a white stripe on each forewing helps identify them in the field.  The caterpillars (hornworms) of this species reach nearly 3 inches in length and can feed on a wide range of plants.  While this species is regularly encountered in the Midwest, this year has been especially good for white-lined sphinx moths in Wisconsin.  In mid-to-late July I received many reports of the caterpillars—sometimes in astounding numbers.  In several instances, “outbreaks” of tens of thousands of these large caterpillars were spotted as they migrated across roadways from agricultural fields.  The multitudes of caterpillars have since pupated and transformed into nectar-loving moths—leading to a recent spike of sightings.

White-lined sphinx moth (Hyles lineata). Photo Credit: Andy Reago & Chrissy McClarren; Wikipedia

In addition to the white-lined sphinx moth, several other hummingbird-like sphinx moths have been common this year—the “clearwing” hummingbird moths (Hemaris spp.) and the Nessus sphinx moth (Amphion floridensis).

The rusty-colored “clearwing” moths (Hemaris spp.) are smaller than the white-lined sphinx moth, and have a wingspan of approximately 2 inches.  Their shaggy appearance and patches of yellow coloration lend a resemblance to large bumble bees.  Characteristic transparent “windows” in the wings help identify these moths.  Several Hemaris species can be encountered in the Great Lakes region with subtle differences in appearance and biology.  Both the “hummingbird clearwing” (Hemaris thysbe) and the “snowberry clearwing” (Hemaris diffinis) can be common, while the “slender clearwing” (Hemaris gracilis) is associated with pine barrens and is rarely encountered.

The hummingbird clearwing moth (Hemaris thysbe) showing the transparent “windows” in the wings. Photo Credit: Andy Reago & Chrissy McClarren; Wikipedia

The “Nessus Sphinx” (Amphion floridensis) is another hummingbird mimic that was commonly reported earlier in the summer.  Although somewhat similar in size and coloration to the Hemaris clearwing species, the Nessus sphinx moth has opaque wings and two distinct yellow bands across the abdomen.

The Nessus sphinx moth (Amphion floridensis) in action. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

In addition to being a joy to observe, sphinx moths are a great example of “non-bee” pollinators.  Their unique behavior and anatomy allows them to form interesting relationships with some of the plants they pollinate.  In an extreme example, the Christmas Star Orchid (Angraecum sesquipedale) from Madagascar possess extremely long tube-like floral structures which contain the nectar.  Upon learning of the unique anatomy of this orchid, the famed naturalist Charles Darwin speculated that a moth with equally long mouthparts must exist to pollinate them.  It took over a century to document, but a sphinx moth wielding foot-long mouthparts was finally observed pollinating the Christmas Star Orchid.

Sawflies: Caterpillar Copycats

As the old saying goes: if it looks like a duck, swims like a duck, and quacks like a duck, it’s probably a duck.  Following that logic: if it looks like a caterpillar, walks like a caterpillar,  and feeds on plants like a caterpillar, it’s probably a caterpillar—right?

This isn’t always the case and one important example would be the sawflies.  Sawfly larvae look an awful lot like true caterpillars (which turn into moths or butterflies), but these creatures are actually related to ants, bees and wasps.  In contrast, adult sawflies have a distinct wasp-like appearance which hints at the true evolutionary relationships of these creatures.

Elm sawfly adult. The wasp-like appearance reflects the relationship of sawflies to ants, bees, and wasps.

With a little know-how, you can learn to tell apart sawfly larvae from true caterpillars. In addition to three pairs of true jointed legs on the thorax, true caterpillars possess 4-5 pairs (or fewer for “inchworms”) of stubby, blob-like prolegs on their abdomen—each tipped with tiny velcro-like hooks (crochets) that can be seen under magnification.  Sawflies have more pairs of prolegs (7 pairs) and lack crochets.

Larva of the dogwood sawfly. Note the strong resemblance to a caterpillar, but this larva has seven pairs of stubby prolegs on the abdomen.

There are dozens of sawfly species in the Midwest, some of which can be considered plant pests, while others can go unnoticed due to their small size or cryptic habits.  The commonest sawfly species can be pests of pines and other conifers, elms, birches, and other hardwoods, and ornamental flowers and shrubs such as dogwoods, roses, and columbines.  If you’ve ever spent time thumbing through a caterpillar guide book and can’t seem to find a match, there’s always a chance you might be looking at a sawfly.

To further explore the world of sawflies, check out this article from the Wisconsin Master Gardener Program.

Wisconsin’s Top Insect Trends of 2015 (#5 – #1)

In this post, we’re continuing to count-down 2015’s top insect trends in the state.  This is the final post in a three part series.  Part I (2015’s diagnostic lab statistics) can be found here and Part II (Top Insect Trends Numbers 10-6) can be found here.

5) Pollinators
With all the headlines about bees, it’s not surprising to see pollinators in the top insect stories again in 2015.  Similar to other years in the recent past, honeybees and other pollinators have been facing declines.  Unfortunately, Wisconsin saw some of the highest honeybee losses in the country, with over 60% colony loss during the 2014-2015 period.  Some good news over the past year has been the development and release of pollinator protection plans.  A federal pollinator protection plan was released in May with the goals of reducing honeybee losses, increasing the population of Monarch butterflies, and increasing pollinator habitat.  In addition, a Wisconsin pollinator protection plan was announced in 2015, and was just released in January of 2016.   Due to the recent declines and their importance to agriculture in the state and nation, pollinators will continue to be in the spotlight in the future.

A ground nesting bee (Colletes sp.) near the stump of the former President's Oak on the UW-Madison campus. Photo Credit: PJ Liesch
A ground nesting bee near the stump of the former President’s Oak on the UW-Madison campus. Photo Credit: PJ Liesch

4) Spring caterpillars
An unexpected insect trend in the spring of 2015 was the surprising abundance of a number of caterpillar species feeding on plants in the landscape.  Caterpillar species, such as the humped green fruitworm, speckled green fruitworm, eastern tent caterpillar, forest tent caterpillar, gypsy moth caterpillar, and the euonymous caterpillar are typically present to some extent, although their numbers have been low the past few years.  For a number of potential reasons, these species had a great spring and during a period in May and June, caterpillars made up roughly 30% of the cases coming in to the diagnostic lab.  Weather patterns (i.e., rainy weather) and natural predators/parasites/diseases can have significant impacts on caterpillar populations each year, so it’ll be interesting to see if we’re faced with a plethora of caterpillars again in 2016.  Additional details of this story were featured in a blog post last June.

3) Viburnum Leaf Beetle
In terms of a new emerging pest with the potential to impact a commonly planted landscape shrub, Viburnum Leaf Beetle is near the top of the list.  As of late 2014, we only knew of a single infested viburnum bush in northern Milwaukee County, which raised the question: is the infestation small enough to contain and/or eradicate?  Some ground truthing this past spring identified many new infestations in SE Wisconsin, in many cases miles from the original site.  At the moment, the viburnum leaf beetle seems to be centered around the four county area where Milwaukee, Waukesha, Washington, and Ozaukee counties meet.  While this insect only feeds on viburnums (and related plants like Arrowwood), the damage can be significant.  It may be some time before this pest spreads elsewhere in the state, but if you have viburnum plants in your yard in SE Wisconsin, be weary!  Additional details of this case were featured in a post last June.

VLB Damage
“Skeletonizing” feeding damage from adult viburnum leaf beetles. Photo courtesy of Paul Weston, Cornell University, Bugwood.org

2) Brown Marmorated Stink Bug
Populations of the invasive Brown Marmorated Stink Bug increased dramatically in 2015 and this insect takes the overall #2 spot in this list (up from #8 last year).  This invasive species was first spotted in the state in 2010, and each year a handful of lone adults have been found in Wisconsin.  In the fall of 2015, we had more sightings of BMSB (30+), than in the past 5 years combined! (Spoiler: this trend has continued into early 2016)  At this point, the “hot spots” in the state are: Dane County, the greater Milwaukee area, and the Fox River Valley.  In addition to being an indoor nuisance pest, BMSB can also feed on and damage a wide variety of plants in home gardens, agricultural fields and orchards.  In other places in the country, the first reports of plant damage have typically been noted ~3-5 years after the initial detection of this species.  With that said, 2016 could be the year that BMSB really takes off and starts wreaking havoc for gardeners and agricultural growers alike.  Additional details of this case can be found in this post from last October.

1) Magnolia Scale
While scale insects have already been mentioned in the “sucking insects” section (#9 on the list), one species in particular, the Magnolia scale (Neolecanium cornuparvum), seemed to stand out amongst all other insects in 2015.  This species is often present in low numbers in the state, but the conditions must have been perfect for their populations to explode last year.  During the months of June and July, reports of Magnolia scale were coming in on almost a daily basis.  Being one of the unusual scale insects, Magnolia scale adults look more like a fungus than an insect (note the whitish blobs in the image below).  Not only did this bizarre looking species pummel Magnolia shrubs and trees in many parts of the state, but the honeydew produced by these insects rained down below, attracting ants and yellowjackets and leading to the growth of unsightly black sooty mold.  A number of predators, parasites, and diseases typically keep Magnolia scale in check, but with the extremely high infestations noted last year, it’s likely that we’ll continue to see some Magnolia scale activity into 2016.  If you experienced magnolia scales first hand, there’s a helpful factsheet available here.

Magnolia twig coated with whitish, fuzzy magnolia scale adults.

Spring is Caterpillar Season

Caterpillars, and the moths and butterflies they become (Order Lepidoptera), normally make up less than 20% of the cases in the diagnostic lab, while beetles (Order Coleoptera) usually make up the largest chunk of the pie (almost 30%).  However, spring often tells a slightly different story around the lab:Pie Chart-May 2015So what does this mean? Well, as far as caterpillars are concerned, it’s been a great spring in Wisconsin. Perhaps you’ve even noticed some happily munching on the trees and shrubs in your yard. If you’re curious to meet the culprits, there’s a good chance they’re on this list:

1) Speckled Green Fruitworm
2) Humped Green Fruitworm
3) Linden Looper
4) Gypsy Moth
5) Eastern Tent Caterpillar
6) Forest Tent Caterpillar
7) Euonymus Caterpillar

Of all the caterpillar species that have popped up this spring, the speckled green fruitworm (Orthosia hibisci) has been the biggest surprise. It’s usually present, but in low enough numbers that damage isn’t common. Despite having the word “fruit” in its name, this species feeds on more than just fruit trees—it also feeds on a long list of hardwood trees and shrubs and even some conifers. This spring I’ve had reports of it damaging: maples, oaks, hackberry, lindens, elm, serviceberry, apple, spruce, peonies, roses, and other plants.

Speckled Green Fruitworm
Speckled green fruitworm on a rose bush in Madison, WI. Photo credit: PJ Liesch, UW-Entomology

The humped green fruitworm (Amphipyra pyramidoides), has a similar feeding pattern to its speckled cousin and has also been common this spring. An interesting thing about the green humped fruitworm is that the caterpillars turn into copper underwing moths. Perhaps that name sounds vaguely familiar? If you’ve been following this blog, you may remember the invasion of the copper underwings from last summer. It’s too early to tell, but with the numbers of green humped fruitworm caterpillars I’ve been seeing, I wonder if we might see the copper-colored adults sneaking into buildings again in the coming months. . .

Green Humped Fruitworm
Green humped fruitworm on a rock near Coloma, WI. Photo credit: PJ Liesch, UW-Entomology

Like the fruitworms, the linden looper (Erannis tiliariaa type of inchworm) and the nefarious gypsy moth (Lymantria dispar) also feed on a wide range of plants and have been popping up this spring. I haven’t had any reports of large-scale significant defoliation by gypsy moth, but there are pockets of damage and gypsy moth certainly seems to be more active than last year at this time. Hopefully with the rains we’ve had lately, the fungal disease, Entomophaga maimaiga, will pop up to smack down the gypsy moth numbers.

Linden Looper
Linden looper caterpillar from Middleton, WI. Photo credit: PJ Liesch, UW-Entomology
Gypsy Moth
Gypsy moth caterpillar from Monona, WI. Photo credit: PJ Liesch, UW-Entomology

Then there are the “tent” caterpillars, which have also been common this spring: the eastern tent caterpillar (Malacosoma americana) and the forest tent caterpillar (Malacosoma disstria). The eastern tent caterpillar is the species that makes the silken tents in apple, crabapple, and black cherry trees where the branches meet the trunk of the tree. Despite its name, the closely related forest tent caterpillar doesn’t make any tents…

Eastern tent caterpillar near Coloma, WI. Photo credit: PJ Liesch, UW-Entomology.
Eastern tent caterpillar near Coloma, WI. Photo credit: PJ Liesch, UW-Entomology
Forest tent caterpillar near Coloma, WI. Photo credit: PJ Liesch, UW-Entomology.
Forest tent caterpillar near Coloma, WI. Photo credit: PJ Liesch, UW-Entomology

Lastly, if you’ve got a burning bush (Euonymus alatus) or another type of euonymus, you might have noticed some webbing on your plant from the euonymus caterpillar (Yponomeuta cagnagella). In some cases, the webbing from these polka-dotted caterpillars can cover the entire plant, making you think that giant mutant spiders have taken over. Complete defoliation can occur with this species, but thankfully, most healthy plants leaf out again and are generally fine.

Euonymus caterpillar and webbing on burning bush near Cambridge, WI. Photo Credit: PJ Liesch, UW-Entomology
Euonymus caterpillar and webbing on burning bush near Cambridge, WI. Photo Credit: PJ Liesch, UW-Entomology

Now for some good news: while all of these spring caterpillars have the potential to significantly damage plants, they only have a single generation per year—meaning that they’re just about done wreaking havoc for the year in the southern part of the state. That’ll give us just enough time to get ready for the next batch of insects coming up soon: squash vine borer, squash bugs, Japanese beetles and many more!

How to Keep Your Mind off the Early Winter

First, daylight savings time ends leaving it dark in the late afternoon.  In the time it takes you to say Catoptrichus frankenhauseri three times quickly, the snowflakes are flying again.  Then there’s the winter driving conditions.  The worst part of it all (from an entomologist’s perspective) is there simply aren’t as many insects to find during the Wisconsin winter.  [Although, I can assure you there are still insects to find if you know where to look. . .Before you know it, the conditions will be just right to look for snow scorpionflies, winter stoneflies, snow fleas and others, but I’ll save that for another time.]

For those that aren’t daydreaming about collecting insects off the frozen tundra, there’s nothing better to get your mind off the flurries outside than thinking about some cool insect cases from this past year (bonus: there’s even green leaves in the images).  One of the prettiest insects that popped up in the lab this summer was the caterpillar of the Funerary Dagger Moth (Acronicta funeralis).  This curious critter is sometimes called a “paddle caterpillar” due to the paddle-like structures that dangle from the jet-black and yellow-spotted body.  Not only is this one of the neatest looking and most distinctive caterpillars out there, but it also has the distinction of gracing the cover of David Wagner’s “Owlet Caterpillars of Eastern North America”, one of the best caterpillar guides available.

Funerary
Funerary Dagger Moth Caterpillar (Acronicta funeralis); Photo credit DZ Johnson

It’s not a very common species, but has been documented from much of the eastern US.  The caterpillars feed on maples and a number of other trees and shrubs.

Funerary Dagger Moth Caterpillar (Acronicta funeralis); Photo credit DZ Johnson
Funerary Dagger Moth Caterpillar (Acronicta funeralis); Photo credit DZ Johnson

 

Tobacco Hornworm et al.

It’s not unusual for gardeners to find large caterpillars of the Tobacco Hornworm munching on their tomato or pepper plants.  Hornworm caterpillars get their name from the horn-like structure at the back end of the insect and while many species of hornworm caterpillars are known from Wisconsin, the tobacco hornworm is one of the largest and can reach lengths of over 3″.  If all goes well, the caterpillars eventually transform into large, grayish sphinx moths with a series of yellowish dots on the sides of the abdomen.

However, tiny parasitic wasps will sometimes kill a caterpillar before it can turn into an adult moth.  Female Cotesia wasps inject eggs into a tobacco hornworm caterpillar and the developing wasp larvae live as internal parasites.  At a certain point, the wasp larvae have matured and move to the outside of the caterpillar to spin silken cocoons and transform into adult wasps.  Biological control in action!

Hornworm
Tobacco hornworm caterpillar with dozen of cocoons from parasitic wasps. Photo courtesy of Deb Zaring.