Ashleigh Edmonston of Ardgowan School asks :-

If an animal which has venom bites itself, will it die?

Simon Pollard, an arachnologist at Canterbury Museum whose research on spiders that live in pitcher plants featured in a recent BBC series Planet Earth, and who has just returned from Kenya where he has been working on blood-drinking jumping spiders, responded.

Animals use venom to paralyse or kill prey and to defend themselves. For example, spiders have a pair of venom glands and fangs, which work like two syringes. The venom glands have a special lining to stop the venom they contain from damaging the spider, just as our stomach has a lining to stop us from digesting ourselves.

When a spider injects venom into an insect or a dentist injects you with an anaesthetic, both the venom and the anaesthetic travel through blood vessels to the brain. The spider venom damages the insect's brain and the insect stops moving, making it easier for the spider to feed. The anaesthetic makes you unconscious, making it easier for the dentist to work on your teeth. The drugs work because they travelled in their original form, through the blood stream to the brain of both animals.

However, if you and the insect had swallowed the anaesthetic and venom, respectively, it would have had no effect. Digestive enzymes in both your stomachs would have broken down these complex molecules into simpler harmless forms. Consequently, when a spider eats an insect it has injected with venom, it does not suffer any harmful effects from its own venom, because digestive fluid breaks down the poison. But, if a spider bit itself and injected venom into its own body, the venom would kill it. Many spiders are cannibals and some even specialise in eating other spider species. In both cases their venom is effective because it is injected into the victim's body.