Caterpillar Hunt
Saturday, May 19, 2009

Ecologist John Lill led a group of 15 adults and children on our second Caterpillar Hunt, this one in the Kemp Mill area just below Colt Terrace. He pointed out that caterpillars are among the fastest-growing organisms in nature, increasing in mass 1,000-fold as they mature from egg to larva. He noted that locally, black cherry and oaks are particularly rich in caterpillar variety, tulip tree less so, with maples hosting somewhat fewer still. The cherry hosts many species even though the leaves produce a form of cyanide that is activated upon chewing. Tent caterpillars, among others, have evolved a metabolism that counteracts the poison. John is an insect-plant ecologist at George Washington University, specializing in forest caterpillars.

John showed us how beating on tree limbs can drop unseen caterpillars
onto a white sheet for easier collecting.

The most abundant species we found was the Eastern Tent Caterpillar. John explained that their “tents” provide a thermo-regulated environment for young caterpillars, cooling them on hot days and protecting them from cold on chilly days. By the time of our hunt, these caterpillars had reached their “wandering” phase, when they abandon the tent to travel far and wide in search of a suitable location to form their cocoons and pupate. As pupae, the insects will undergo metamorphosis yielding adult moths sometime in late June or early July.

Last year we saw a number of Gypsy Moth caterpillars, but this year we found only one.

Our sharp-eyed families found tiny caterpillars in the inchworm family (Geometridae). Numbering in the hundreds of species, this group of caterpillars serves as a staple in the diet of migrating and nesting birds.

The first photo shows an unidentified species, while the minute specimen
on the right is a tulip tree beauty (Epimecis hortaria).

John also brought along some additional samples of Geometrids he collected the day before, including the Half-Wing moth caterpillar (Phigalia titea), an excellent stick mimic. It feeds only on the newest foliage and will starve if provided only with mature leaves.

This member of the Geometridae family is the fall cankerworm (Alsophila pometaria). Later in the year, the adult female moth pushes its eggs into bark crevices, where they overwinter. Upon hatching, caterpillars like this one drop down on silken threads to be carried off by spring breezes that disperse the population. Some fall cankerworms reproduce without mating, a phenomenon known as ‘parthenogenesis’ which is unusual among butterflies and moths.

Another type of caterpillar we found was this Oak Leafroller, a member of the Tortricid family of micro-moths. These caterpillars hide themselves in the daytime in leaves either rolled-up or webbed together with silk.

We also found one member of the Owlet Moth family (Noctuidae), the largest family of moths and butterflies with more than 35,000 species world wide. This is probably the Intractable Quaker Moth (Himella intractata).

We found just one butterfly specimen, this puparium of a species in the Brush-footed butterfly family (Nymphalidae), which includes the fritillaries, mourning cloak, red admiral, painted lady, and buckeye.