A prickly American caterpillar's trauma-inducing venom can punch a hole in cells thanks to a mechanism inherited 400 million years ago from bacteria, a team of Australian scientists said Tuesday.

The asp caterpillar, which has a predilection for oak and elm trees in its native North America, looks almost innocuous, with bristles that resemble fur.

But those bristles conceal spines that can deliver "an excruciating sting likened to touching burning coal or blunt force trauma -- often sending victims to hospital", said researchers at Australia's University of Queensland.

Scientists found its venom was unlike anything seen before in insects, said Andrew Walker, who led the molecular bioscience research team.

Its proteins are like the toxins produced by bacteria such as E. coli and Salmonella, which stick to cell surfaces and assemble into donut-like structures that form holes, the team said.

"The venom in these caterpillars has evolved via the transfer of genes from bacteria more than 400 million years ago," Walker said.

Such toxins may have particular potential in future drug delivery because of their ability to enter cells, he added.