Caterpillars are probably not the first animals that spring to mind when you think of venomous creatures. Naturally, snakes. Spiders and scorpions, too. However, caterpillars?

Yes, exactly. There are hundreds, if not thousands, of venomous caterpillar species in the world, and at least some of them are toxic enough to kill or seriously harm a human. Scientists study them for that reason alone. However, the toxic secretions of caterpillars also contain a potential treasure trove of medicinally beneficial compounds.


Will we reach a point where we can extract useful substances from their venoms? Indeed, according to Andrew Walker, a biochemist and evolutionary biologist at the University of Queensland in Australia. However, a lot of foundational work needs to be done.

Caterpillars are the larval stages of the insect order Lepidoptera, the butterflies and moths. It’s just one of many animal groups with little-known venomous members. (Venoms are toxins that are deliberately injected into another animal, while poisons sit passively in an organism’s body, waiting to sicken a potential predator.) By biologists’ best estimate, venoms have evolved at least 100 times across the animal kingdom.

Many venoms are complex, some containing more than 100 different compounds. And they’re also strikingly diverse. “No two species have the same venom arsenal,” says Mandë Holford, a venom scientist at Hunter College and the American Museum of Natural History in New York City. “That’s why it’s important to study as many species as we can find.”

Indeed, studying venoms could be a better way to find new drug candidates than starting from scratch, because they contain molecules fine-tuned over eons to target specific biological processes in the victim. “They’ve evolved over millions of years, they’ve been tested in nature, and we know they work,” says Holford. “When we try to devise them ourselves in the lab, the success rate is a lot less.”

Most groups of venomous organisms, however, are barely on scientists’ radar. “We have a huge wealth of knowledge about snake venoms and scorpion venoms and spider venoms,” says Nicholas Casewell, a venom biologist at the Liverpool School of Tropical Medicine in the UK. “But there are lots of groups of venomous animals out there that are largely unstudied.”

Caterpillars, in particular, deserve more attention, says Walker, who wrote about venomous Lepidoptera in the 2025 Annual Review of Entomology. Though only about 2 percent of caterpillar species are venomous, by Walker’s estimate, they’re widely scattered across the lepidopteran evolutionary tree. That pattern means venom likely evolved independently several times within the group, potentially yielding an unusual diversity of chemicals. The deadly caterpillars — within the South American genus called Lonomia — have a snakelike venom that interferes with blood clotting. Others have venoms that cause chronic, lifelong inflammatory problems, and a couple cause miscarriages in horses.

Those nasty few are enough to make venomous caterpillars a significant public health issue, in at least some parts of the world, says Walker. “They’re not killing many people regularly like scorpions and snakes do, but compared to spiders there’s not much difference in the impact of the health hazard.” The concern has led some researchers to work on understanding the biological effects of the potentially lethal Lonomia venom, and to develop antivenom to treat affected people.

Though a few other caterpillar venoms have been studied at least a little, most remain almost entirely unstudied, says Walker — and medicine may be missing out. For example, he notes, most lepidopteran venoms cause pain, sometimes intense enough to require opioid painkillers. That’s not surprising, since pain is an excellent way to deter predators — but it also allows researchers to use the venom as a probe to identify pain pathways in the body and pain receptors in lab animals and, potentially, in people. That, in turn, could lead to new drugs.

Research on caterpillar venoms is still sparse enough that no new drugs have resulted yet, but venoms of other organisms have yielded some important therapies. There are blood-pressure and anticlotting medications that were inspired by snake venoms, for example, and a forerunner to the new blockbuster drug semaglutide — better known by brand names such as Ozempic and Wegovy — was based on a molecule extracted from a venomous lizard, the Gila monster.

Thanks to advances in molecular biology and bioinformatics, venoms of all animals, including caterpillars, are increasingly easy to investigate — and that should mean big steps forward soon, says Casewell. “It’s like a treasure trove that’s still sitting out there for us to understand.”