Monday, April 27, 2009

It's Getting Cuckoo

Forest tent caterpillar weave masses of white silk in deciduous trees. They shelter in the "tents" and emerge to eat the trees new leaves.

This is the time of year when the trees are leafing out—or trying to leaf out. If a tree is unlucky enough to be infested with forest tent caterpillars, it may have a hard time getting its first batch of leaves out before they are devoured by the tent caterpillars. The caterpillars favor broad-leaved deciduous trees, especially oaks, maples, aspens, and on our farm, ashes and cherries.

The first part of the life cycle of the forest tent caterpillar goes like this: tiny (1/8th of an inch) caterpillars hatch from eggs and begin feeding on newly emerged leaves. The caterpillars congregate into colonies on favorite food trees, which they find by following silken trails laid down by others of their kind that are searching for a new food source. The caterpillars go through five instars or molts before reaching their full-grown size of two inches. While molting or between bouts of feeding, the colonies of caterpillars form large silken mats on a tree, often at the junction of branches and the trunk.

The caterpillars can defoliate a tree in a matter of days. If you stand near a tree that is actively being fed upon by these hungry "cats" you can hear their frass (poop) dropping to the forest floor. Only rarely does the caterpillars' defoliating of a tree result in the tree's death, and then, only with trees that were already otherwise compromised.

The complete life cycle of the forest tent caterpillar, including the riveting portion of their lives when they spin a cocoon and emerge as a moth, can be found here.

These forest tent caterpillars are nearly full-sized.

For now, I'm sticking with the "tents" and the caterpillars that are in them. I know that when I see the white masses of silk, crawling with caterpillars, that it's almost time for the cuckoos to arrive in spring migration. Many's the time I've seen yellow-billed cuckoos chowing down on these hairy crawlies, but the ornithological literature and all the smart people that you find on The Google, indicate that as many as 60 bird species take advantage of forest tent caterpillars as a food source. The list of 60 bird species includes nuthatches, warblers, orioles, blackbirds, grosbeaks, jays, and waxwings. Many birds also steal the silk from the "tents" to use in nest building, including the blue-gray gnatcatcher, as seen here in a BOTB post from 2006.

Yellow-billed cuckoo, an avid eater of tent caterpillars.

For me, the appearance of the blobs of white silk and the dark caterpillars crawling all over the son-to-be-leafless trees, means only one thing: It's cuckoo time!

Labels: , ,