Fall Webworm

Over the years many people have asked about the “tent caterpillars” that appear on hardwood trees in the late summer and fall. I’ve explained to them that these aren’t eastern tent caterpillars but are instead the webs of the fall webworm (Hyphantria cunea) that have both a very different life history and very different impact on the trees they inhabit than do tent caterpillars. 

From Bugwood.org

The webs we see on hardwood trees in the fall are formed by the caterpillars of an insect that as an adult is a non-nondescript white moth having a wingspan of about three-quarters of an inch. Fall webworm caterpillars hatch from eggs that the female moth lays on the underside of leaves in early summer. Newly hatched larvae begin to spin a web to enclose the branch-tip leaves on which they feed. As the caterpillars grow they enlarge the web to cover more and more leaves and eventually the webs become large enough to attract the attention of the people who ask about the “tent caterpillars”.

The webs are quite tough and easily defeat the efforts of most birds and small mammals that would otherwise prey on the caterpillars. If the web is breached, the caterpillars immediately drop from the web. Those that fall to the ground have little chance of survival, but if they merely fall to a lower branch they have a remote chance of returning to the web or creating a new web on the host tree.

As the days shorten and the caterpillars mature they emerge from the webs, drop to the ground and pupate over winter in the leaf litter on the ground or in the soil. The adults emerge in late spring or early summer, mate, lay eggs and die.

Because fall webworm caterpillars only feed in late summer and fall, their impact on host trees is minimal. The trees have already formed the leaf and flower buds for next year and have manufactured virtually all of the sugars they need to survive the winter and grow the following spring. However, the webs sure are ugly and often hang on the trees all winter – their impact on aesthetics can be significant. 

Just as invasive exotic species are a problem in our forests, fall webworms have become invasive in Europe and Asia after their accidental introductions in Europe and Japan during the 1940s. 

So how do fall webworms differ from the eastern tent caterpillars with which they are so often confused? Tent caterpillars build their tents in the spring; fall webworms, true to their name, are active in the fall. Tent caterpillars can defoliate entire trees and even kill small trees; fall webworms seldom do either. Tent caterpillars typically use their webs to hide from predators but leave their webs to feed; fall webworms feed within their webs. Tent caterpillar webs are in the crotches of trees –

Fall webworm webs are on the tips of branches –

Bear-ly More Than A Fortnight

Fortnight -- noun \ˈfȯrt-ˌnīt\ : a period of 14 days : two weeks 

In a bit more than two weeks – 16 days to be exact – three of my camera traps captured photos of black bears on eight different days. This summer the cameras have gotten pictures of opossums, gray squirrels, porcupines, raccoons, coyotes, bobcats, wild turkeys and white-tailed deer but black bear has been the predominant species in the photographs a sampling:

Day 1

Day 3

Day 4

The next week ushered in the hottest week of the summer, with temperatures approaching 90° and humidity to match. Activity was seemingly focused at the vernal pool, with the bears coming to wallow in the relatively cool water.

Day 10

Day 11

Day 11

Day 11

Day 13

Day 14

Day 16

Day 16

Wildlife always raises questions. Where were the bears during those six days? How far do they travel to wallow in the pool? How many different bears visit the pool and what are their interactions? There's a not too distant stream that is cooler than the stagnant pool, do they also soak there?

Hummingbird Clearwings

A couple of weeks ago I walked through the largest patch of wild bergamot (Monarda fistulosa) that I’ve ever seen – it covered well over two acres of an old field that’s gradually reverting to forest. Wild bergamot is a lavender flowering species in the same genus as the more familiar bergamot called “bee balm” or “Oswego tea”.

Flying rapidly from flower to flower was what at first glance could easily be mistaken for a hummingbird. But it wasn’t, it was actually an insect – a hummingbird clearwing moth (Hemaris thysbe).

Except for three other closely related species, hummingbird clearwings are unlike any other moth. Most obviously, they fly by day sipping nectar from a wide variety of flowers.

The second obvious feature of these moths is their transparent wings; the center portion of both the forewings and hind wings is transparent. So much so that details of objects behind the wings can be clearly distinguished.

As they fly, their long proboscis is coiled, but it’s extended as they approach a flower.

They spend only a second or two with their proboscis inserted into any individual flower, then move on to another.

The hummingbird clearwing moth is about half the size of the ruby-throated hummingbirds that feed on the nectar of many of the same species of flowers. The large patch of wild bergamot in this old field had attracted numerous hummingbird clearwings that flew so rapidly from flower to flower that it was difficult to get a decent photograph.