LONDON - Tarantulas and chili peppers may not appear to have anything in common, but an encounter with either the spider or the plant can be a painful experience.

Scientists at the University of California at San Francisco have discovered that they use similar tactics to frighten off predators by causing pain.

The venom of tarantula Psalmopoeus cambridgei, which is a native species in Trinidad and Tobago, contains toxins that trigger the same pain receptor on nerve cells throughout the body as hot chili peppers.

Capsaicin, the main pungent ingredient in hot chili peppers, sets it off.

“We have identified a new mechanism whereby venoms produce pain, and we have shown it is similar to one used by pepper plants to generate a similar sensation,” said David Julius, a molecular biologist at the university.

Both the spider and the plant have evolved a common mechanism to deter predators, he added.

When Julius and his colleagues, who reported their findings this week in the journal Nature, tested the venom of the spider in the laboratory on cells that contained the receptor it sparked a response, but not in the cells without the receptor.

The researchers also isolated three compounds from the spider venom. Mice with the receptor showed signs of pain and inflammation when the compounds were applied to their paw.

But there was no response in transgenic mice without the receptor.

The researchers whose work is focused on understanding the molecular basis of pain sensation believe other spiders may also use a similar defense mechanism.