Heads or Tails?

What am I looking at?

This image shows the caterpillar stage of two slug moths – a blue spun glass slug moth (Isochaetes beutenmuelleri) and a purple monkey slug moth, also called a hag moth (Phobetron pithecium).

Biology in the background

At the caterpillar stage, slug moths use a different defensive strategy than most caterpillars – they are nearly transparent, and their bodies are covered in spiky tubercles that fall off, aiding in the caterpillar’s defense. In later stages, the tubercles of the monkey slug grow longer and curly, giving the caterpillar the appearance of an exoskeleton molted by a spider, an interesting form of mimicry.

These caterpillars live in the eastern United States, with their range extending as far west as Texas and Colorado. They feed on oak and beech trees. The spines on the caterpillars’ sides contain a poison that can irritate your skin if you touch them. Like all Lepidopterans (the order that includes butterflies and moths), slug moths undergo complete metamorphosis.

In the fall, the caterpillars spin oval or spherical cocoons made of brown silk, then overwinter in a state of suspended animation, also called diapause. In the spring, they pupate (form a chrysalis), and the adult moths emerge through a hinged flap at one end of the cocoon in the summer, generally from June through August. The moths are relatively unremarkable in their coloration, which is why they’re named for their visually striking caterpillar stage.

A spun glass caterpillar can grow up to 7 millimeters long, or roughly half the size of a human thumbnail, and a monkey slug caterpillar can grow up to 25 millimeters long, or roughly twice as big as a human thumbnail.

Technique

These images were created using macrophotography.