An African bugleweed synthesises in its tissues a substance similar to the hormone that controls the development of caterpillars. If a caterpillar is persuaded, experimentally, to ingest that substance, then when it turns into a butterfly it will develop two heads and die.*
I'm put in mind of an adolescent gang of caterpillars, urging on the littlest, "G'wan, mate, have a nibble. You're not scared, are you?"
* David Attenborough, The Private Life of Plants, p70.
