An invasive insect

First of all, an update on those cowbirds from last week.

Recent days have revealed a plethora of fledged nestlings of all sorts, particularly rose-breasted grosbeaks and eastern phoebes. Late last week, I looked out in the morning and saw a group of four fluffy juvenile Baltimore orioles lined up on top of the bird feeder hooks, watching their dad demonstrate how to operate the suet feeder.

Tucked in with this group, looking completely at home, was a juvenile brown-headed cowbird. It was about the same size as its foster father and siblings and seemed happy to follow the family around for a few days before wandering off to join the blackbird crew. I do wonder how this baby knows it isn’t an oriole since that’s who raised it, but at any rate it’s off to enjoy its child-free lifestyle.

A recent trip to the Spread Eagle lakes in Florence County highlighted a problem that has been literally plaguing the South Shore area over the past couple of summers. The usually luxuriant oak trees lining South Lake and Long Lake were looking pretty sparse thanks to an invasive pest that’s been in the news since I was a kid: spongy moth caterpillars.

Spongy moths were known as gypsy moths until 2022, when their name got an overhaul as their former name is considered to be a slur by Romany people (Sidebar: I know a lot of people get pretty lathered when a species name gets changed, but I have to ask: Who is really being harmed by referring to a bug as spongy instead of as an ethnic slur?). But whatever their name, this invader from Europe and Asia has been causing problems for arborists and landowners for decades.

Spongy moths were introduced in 1869 by an amateur entomologist hoping to breed a new silkworm that was disease resistant. Being an amateur, he let some of them escape and since then, it’s been the spongy moth’s world and we’re just living in it. Spongy moth caterpillars resemble the native Eastern tent caterpillar, with their spiny hair, but they have a series of red and blue markings instead of the tent caterpillar’s yellow stripe. Tent caterpillar infestations also manifest earlier in the season and fill the trees with their silken shelters.

Infestations of spongy moths (named after their goopy egg masses) tend to spike every 5-10 years depending on weather conditions. Along the South Shore last summer was particularly bad. A visit to a Big Top Chautauqua concert in July 2023 (Gladys Knight was amazing by the way) looked more like November than summer: the oak trees were almost completely denuded. We lost a couple of poplar trees in the town of Gingles (along with one from the summer before thanks to tent caterpillars), but at least those trees will put up suckers and regenerate in the future.

Spongy moths especially like oak and birch trees in our area, and an infestation up in the Bayfield Fruit Loop is problematic for apple growers (it’s also gross trying to pick strawberries that are crawling with bristly caterpillars). But unlike an invasive pest like the emerald ash borer, spongy moths are more of a nuisance than an existential threat to native forests.

In fact, some defoliation can be beneficial to forest health. The increased sunlight creates diversity in the understory and the weakening caused by defoliation weeds out diseased trees. And the larvae and their droppings are great soil fertilizers. Still, two summers of defoliation is hard on any forest, and our warm dry winter supported these pests for another round this year. Persistent infestations leave trees vulnerable to other pests.

Thanks to their spiny texture, spongy moth caterpillars don’t have a lot of persistent predators. Their most persistent predators in our area are black- and yellow-billed cuckoos, and sadly there are just not enough of them to make an impact during an infestation. It’s a good deal for the cuckoos, though; their struggling populations get a boost during caterpillar years, and it’s been fun seeing and hearing them around the past few summers.

Meanwhile, the soaking wet spring and summer we’ve had may already be doing a number on our crawly neighbors. Wet conditions encourage fungal growth that kills off larvae. In fact, the tree trunks along South Lake in Spread Eagle were covered in dead spongy caterpillars last weekend. I’m hopeful that these critters will be less populous next summer and our oak trees can once again provide some shade.