Okay, venom is not popular among non-snakes. But it does demonstrate a point:
A study of spitting cobras, published in Science reveals how a combination of venom components have evolved to create an instantly painful venom, not once, but on three separate occasions.
This is the first clear example of snake venom evolving for defence, and provides a remarkable example of convergent evolution, or how natural selection can cause the same solution to a problem to evolve multiple times.
Contrary to the theory that venoms are adapted primarily to enable snakes to kill prey, in spitting cobras, a venom which causes instant pain, and a delivery system which enables the snake to spray the venom to a distance of up to 2.5 metres towards the eyes of anything which comes too close, suggests a defence mechanism, rather than hunting weaponry.
Bangor University, “Spitting Cobra venom reveals how evolution often finds the same answer to a common problem” at ScienceDaily
The paper is paywalled.
See also: Evolution appears to converge on goals—but in Darwinian terms, is that possible?