The two terms – ‘venomous’ and ‘poisonous’ – are often used interchangeably to describe an organism that deploys toxins for the purposes of attack or defence. Biologically, though, they have specific meanings.
What does venomous mean?
Venomous species such as jellyfish, black widow spiders and adders actively deliver their chemical arsenal into their victim with a bite or sting.
What does poisonous mean?
But poisonous ones – for example ladybirds, poison-arrow frogs and yew berries – are more passive, and only unleash their toxins when nibbled or touched.
However, eat a venomous animal and you could find it proves to be poisonous, too.
Are snakes poisonous or venomous?
Many people call a snake ‘poisonous’ when they mean ‘venomous’. The latter involves injecting prey with a toxin (venom), whereas the former is secreting a defensive toxin (poison) that an attacker would prefer not to touch.
Just two groups of snakes are known to be poisonous. North American garter snakes appear to acquire toxins when they eat newts, at least temporarily.
Asia’s keelback snakes also obtain toxins from prey, this time toads, but retain the noxious chemicals in special glands in their neck. This has been known for a while, but recently scientists discovered a twist in the tale.
One species, the groove-necked keelback of China and Vietnam, feeds on earthworms instead of toads, yet still boasts the unpleasant deterrent. Earthworms don’t possess toxins, so where is this snake getting them?
The researchers found it supplements its wormy diet with firefly larvae which, like toads, manufacture the deadly substances it needs.
by Ben Hoare
How common are venomous mammals?
Venom is used by many species, but its occurrence is relatively rare in mammals. The most famous venomous mammals include slow lorises, which have a toxin-loaded bite, and the male duck-billed platypus, whose hind legs sport venom-delivering spurs.
While these species use venom for defence, certain insectivorous mammals, including solenodons and some shrews, include poisonous substances in their hunting armoury.
We even have one such species in the UK – the water shrew, whose saliva contains venomous proteins. Delivered via a sharp bite, these toxins affect the nervous system and help to immobilise a range of invertebrate prey, including worms, beetles and crustaceans, as well as small fish and amphibians.
Here are 10 of the most venomous animals
Main image: Adder with its tongue out. © Matthew Goodacre/500px/Getty
