This week in the woods, we’ve observed an abundance of insect life and birds that both depend on these insects and keep their populations in check.
While other aphid species tend to defend themselves by excreting noxious chemicals, woolly alder aphids produce curly, waxy white filaments resembling wool. The filaments entangle preying insects and arachnids, and when the sap-sucking aphids gather on their alder and silver maple hosts, they resemble mold or fungus and deter larger predators. It is a good thing that the camouflage doesn’t always fool birds like this purple finch, which had just had a lunch of aphids; otherwise, the native pests could get out of control. In the Autumn 2007 issue of Northern Woodlands, Virginia Barlow shares one calculation about woolly alder aphid populations: “In the absence of enemies, and given plenty of food and good weather, a single female could give rise to over 600 billion offspring in a single season,” she writes. “And, although aphids do commonly number in the range of a million per acre, predators, pathogens, and parasites fortunately abound, and not every photosynthesizing surface is in danger of being covered with their plump bodies.”
Larvae of the asteroid moth, which also goes by the name goldenrod hooded owlet moth, feed through summer and into fall, primarily on late-season flowers like their namesake goldenrod and asters. As this post from the Ohio State University Extension explains, the caterpillars’ coloration varies significantly, usually bright green, sometimes brown, as in this photo by Ann Little, but always with black stripes and a broader yellow stripe down the back.
Unlike other difficult-to-distinguish species in the Symmerista genus, the orange-humped mapleworm (seen here in sugar maple leaf litter in Vershire, Vermont, photographed by Ann Little) feeds almost exclusively on maple leaves in its larval stage, with a strong preference for sugar maple. Like many tree species, sugar maples defend themselves from insect defoliation with bitter tannins; after accumulating in leaves all spring and summer, these compounds now reach their highest concentrations (and highest visibility, as contributors to the brown in fall foliage). This deterrent’s peak effectiveness and the withdrawal of nutrients from leaves coincides with orange-humped mapleworm larvae burrowing into the soil and pupating for the winter.
Just as trees defend themselves against caterpillars, caterpillars defend themselves against their own numerous predators. Without the tough external skeletons of many other insects or the flight of their adult forms, Lepidoptera larvae employ other defenses: disguise as twigs, leaves, bird droppings, or snakes; false eyespots to appear like larger animals; difficult-to-digest hairs or spines; bright coloration that advertises toxicity or poor taste; sheltering on well-defended plants and in silk tents; venting of pesticide-like fog or bad smells from their skin; making high-pitched whistles; dropping from trees on threads; and feeding patterns that prevent leaves from betraying their presence to discerning birds. The orange-humped mapleworm has a false head, which it may raise as distraction, like it does here, and its bright yellows and oranges broadcast its chemical protection.
This blackpoll warbler – in its drab fall plumage and distinguishable from a bay-breasted warbler for its yellow legs seen here and in other photos – dined on what may have been an orange-humped mapleworm in the canopy above the one photographed shortly beforehand. In West Fairlee, Vermont, a blue-headed vireo found itself a larva to eat. Because of caterpillars’ richness in protein and fat, insect-eating birds tend to favor them over other insects when feeding their young and to fuel migration. Blackpolls especially need the energy for the thousands of miles to their wintering grounds; they will double their weight in preparation for their epic autumn journey from the Northeast over the Atlantic Ocean to South America, sometimes non-stop, reaching altitudes as high as 20,000 feet, and with an average speed of 25 miles per hour. Ornithologists Janet and Tim Williams call it the metabolic equivalent of a human running four-minute miles for 80 hours. The researchers found that if blackpolls burned gasoline instead of body fat, they would get 720,000 miles to the gallon.
What have you noticed in the woods this week? Submit a recent photo for possible inclusion in our monthly online Reader Photo Gallery.
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