Caterpillar venom is a complex mixture of toxins

Some animals use venom to capture prey; others use it as a defense against predators. Because the most-studied defensive venoms have relatively few components, biologists assumed that applied to all defensive venoms. But these weapons can be quite complex, according to a new study.

Andrew A. Walker and Glenn F. King of the University of Queensland and coworkers used liquid chromatography/mass spectrometry to analyze venom from Doratifera vulnerans caterpillars, which use venom to protect themselves from predators. The venom was much more complex than the researchers expected. They found 151 peptide and protein toxins from 59 protein families (Proc. Natl. Acad. Sci. U.S.A. 2021, DOI: 10.1073/pnas.2023815118). Defensive venoms in animals such as bees and fish have only a handful of components, whereas predatory venoms in spiders and snakes can have hundreds of components. The most abundant peptide families in the caterpillar venom include analogs of an insect neuropeptide, linear cationic peptides, and cysteine-rich peptides that resemble ones in spider venom.

The researchers don’t know why the caterpillars’ venom is so complex. “It could be that there is a large range of predators, or it could be that the venom is being used in multiple ways that aren’t obvious,” Walker says.

Most of what is known about venomous animals is based on only a few groups of animals, such as snakes and cone snails. As researchers study more types of venomous animals, they could find that complex defensive venoms are common. “It could be that the dogma of ‘simple defensive venoms’ is just wrong,” Walker says.

“It seems clear that the venom of Doratifera vulnerans is very complex, both in terms of chemistry and biological activity,” says Helena Safavi, who studies venoms at the University of Copenhagen. “It’s a very nice study that expands our understanding on the complexity of defensive venoms.”

The complexity of the caterpillar venom “is great news” from the perspective of identifying useful molecules, Walker says. Venom toxins have been used as drugs. “We expect some of these toxins will have interesting 3D structures and biological functions,” he says.