Photo: Long-horned Slug caterpillar, Judy Gallagher
Judy Gallagher is an ASNV board member and a regular surveyor of local wildlife who also captures photos of what she sees, in particular the less common species.
Near the end of August each year, I get together with several nature photographer friends for our annual caterpillar safari. No caterpillar is too small or plain for our group to photograph, but we particularly love finding slug moth caterpillars. With their bizarre shapes and variety in almost every imaginable color, they are the jewels of the caterpillar world.
Abbreviated Button Slug with abdomen up, Judy Gallagher
Slug moths are members of moth family Limacodidae. There are at least 1,800 species worldwide, with approximately 20 species found in Virginia. Adult slug moths are often nondescript. They are hairy, and hold their wings tent-like above their abdomen. Many, but not all, hold their abdomen tips up.
Parasa species caterpillar, showing the slug-like appendages for which the family is named, Judy Gallagher
Unlike most other moths, slug caterpillars lack prolegs, the tiny legs that allow caterpillars to move around. They have sucker-like appendages on their underside and secrete a mucus-like fluid over the appendages, much like a slug, which is why they're called slug moths. Another unusual feature of slug caterpillars is that they withdraw their heads into their thoraxes when at rest.
Some slug caterpillars have spines, and the first instar or growth stage doesn't eat, molting almost immediately into the second instar, which does eat. As with most other caterpillars, first instars of non-spiny slug caterpillars eat. Slug caterpillars feed on deciduous trees, including oaks, hickories, cherry, hornbeam, maples, hackberry, birches and willows. It's rare for them to cause serious injury to their host plant.
Saddleback Caterpillar, Judy Gallagher
The Saddleback caterpillar is the most common local spiny slug caterpillar. As the name implies, it looks like a colorful saddle. Poisonous spines surround the saddle, and those who have encountered these spines liken it to having hand sanitizer on an open wound, except the pain lasts a long time. The brown marking in the middle of the saddle looks like a large eye, repelling some predators.
Saddleback Caterpillar with wasp cocoons, Judy Gallagher
The Saddleback caterpillar’s poisonous spines deter most vertebrate predators, but they don't discourage wasps. A species of braconid wasp uses its ovipositor to lay eggs in the caterpillar. The parasitic wasp larvae feed on the inside of the caterpillar, emerging from the caterpillar to form cocoons.
Spun-glass Slug, Judy Gallagher
The Spun-glass Slug is another captivating spiny caterpillar. Each of the spun-glass arms can break off, depositing painful spines in the unsuspecting victim. This does not harm the caterpillar, and it sheds all its glassy arms before it pupates.
Monkey Slug, Judy Gallagher
The Monkey Slug caterpillar or Hag Moth is another caterpillar with arms. Some scientists think that it mimics a large hairy spider to avoid predation. This may be true for related tropical species that live in an environment where there are large hairy tarantulas, but it seems unlikely for our local species. Like the Spun-glass Slug, the Monkey Slug can lose its spiny arms without real injury. The name Hag Moth comes from the arm appendages that look like a hag's disheveled hair.
Skiff Moth caterpillar, Judy Gallagher
The Skiff Moth caterpillar doesn't have spines, but it blends in well with its surroundings. The brown markings resemble leaf imperfections. The caterpillar secretes droplets when attacked, and this deters some predators. Some Skiff Moth caterpillars have pairs of white spots that mimic the eggs of parasitic flies. This may dissuade a parasitic fly from laying eggs on a caterpillar that looks like it has already been parasitized.
Long-horned Slug caterpillar, Judy Gallagher
And now for a colorful one. The Long-horned Slug caterpillar is resplendent in orange, purple, yellow, and blue-green. Its spines aren't as impressive as those of the Saddleback caterpillar, but its warning coloration tells predators to keep away.
Most slug caterpillars are less than an inch long and several are under 1/2 inch, so searching for slug caterpillars can be challenging. But turn over leaves and you may discover hidden treasure. Be careful though -- some of the jewels sting!
View more of Judy’s Observations from Meadowood articles here.