The body of most limacodid caterpillars is covered with long, brittle spines, which break off easily and lodge into the skin of anybody foolish or unlucky enough to get in contact with them. Each spine is connected to a small venom gland and is filled with a mix of compounds, among them histamines and formic acid. These toxins tap right into our nociceptors (pain receptors), and produce immediate sharp pain, followed by swelling or rash. Not surprisingly, these insects have few natural enemies, and those that attack them do so by being able to hit them between the spines, and thus avoid being stung.
Many species of limacodids advertise their unpleasant properties with beautiful, striking colors, employing the principle that is known to every bird and lizard, but one that we humans often forget: if it’s pretty, it’s gonna hurt you. But I knew that when I was photographing a cluster of threateningly black and yellow slug caterpillars in a rainforest of Suriname, and was very careful not to brush against them. It all went very well, that is until I got a little too close and the liana on which they were sitting snapped back, and all of them smacked against the palm of my hand. My screams were apparently heard half a mile away, and I had no use of my arm for the next 24 hours.
Adult limacodid moths lack any formidable defenses, and instead rely on crypsis, blending into their surroundings. Some, like Costa Rican Perola producta, are difficult to identify at first sight as moths even by seasoned entomologists.