At this time of year, several species of caterpillars become obvious feeding on trees. Control is relatively simple if deemed necessary. Many caterpillars feed in groups, where removal by hand or pruning is effective. They are controlled with Bacillus thuringiensis kurstaki, sold as Dipel, Thuricide, and other brand names, as well as by many other insecticides. In the last issue, fall webworm, mimosa webworm, and white-marked tussock moth were addressed. In this issue, additional common summer caterpillars are described.
Yellownecked caterpillar feeds in groups, defoliating large branches. Young larvae are reddish, with white stripes; older larvae are black, with eight broad, white to yellow stripes and a yellow to reddish “neck” dorsally behind the head. Mature caterpillars are about 2 inches long. When disturbed, all in a group raise the front and hind portions of their bodies quickly in unison. They may be first noticed by the large feces, produced in large quantities. The feces (black, barrel-shaped, up to 3/16 inch long) is noticeable when attacked trees overhang driveways, streets, sidewalks, and patios. Yellownecked caterpillars are common on oaks, walnut, hickories, maple, and other trees.
Walnut and sumac caterpillars are similar in size and habits to their close relative, the yellownecked caterpillar. Walnut caterpillar is found mainly on walnut, butternut, pecan, and hickories. It is similar in color to yellownecked caterpillar except it has only a few, narrow, white stripes, no yellow or red “neck,” and long, obvious, white hair as a mature, black larva. Sumac caterpillar feeds on sumac, including ornamentals. It is similar in appearance to the yellow-necked caterpillar, with eight broad, yellow stripes; but the body stays reddish even in mature larvae. Like the yellownecked, both species strip large branches of their leaves and produce noticeable feces.
Cecropia and typically feed singly on oak, elm, maple, and other trees but develop into huge, green caterpillars 4 to 6 inches long, with diameters up to 1 inch. Cecropia caterpillars have two rows of large, bright red and yellow protrusions running down the back, with blue protrusions down the side. Polyphemus caterpillars have thin, diagonal white stripes without colorful balls or other protrusions. Although many leaves are eaten per caterpillar, control is rarely instituted because the caterpillars are so large and unusual in appearance.
Hickory horned devil is another large, solitary, green caterpillar that eats many leaves to achieve its 4- to 6-inch length. This caterpillar has several long, orange horns with black tips protruding dorsally from behind the head and some short, black horns at the posterior. It feeds on walnut, hickory, sycamore, sweet gum, ash, and other trees.