Huge Female, Small Male

July 7, 2003 — For the first time, scientists have identified a member of the animal kingdom that dies spontaneously during sex.

While other animals, such as salmon and mayflies, die shortly after mating, the male Argiope aurantia is the first known species for which mating is an instantaneous trigger for death.

According to a paper published in the current Royal Society Biology Letters, the male spider must insert both of his sexual organs, called palps, into the female's genital opening. Death happens just after insertion of the second palp.

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"The exact physiological mechanisms leading to death are unknown," said biologist Matthias Foellmer of Concordia University in Canada, and co-author of the paper with Daphne Fairbairn of the University of California, Riverside. "I can only speculate that males experience something similar to an irreversible seizure."

After observing 115 matings both in the wild and captivity, Foellmer and Fairbairn were able to document when the males died. Since death occurs during sex, the body of the dead male remains attached to the female by the swollen second palp. This suggests an evolutionary reason for the seemingly untimely demise.

"Dead males stuck in the female prevent other males from copulating in many cases, because males often fail to pull the dead male out of the female, although they try hard," explained Foellmer. "Therefore, dead males probably act as whole body mating plugs when mating with molting females (when the females slip out of their old exoskeletons). The female cannot pull the male out for at least 15-20 minutes."

This delay is critical, according to Foellmer, because the female generally tires and returns to her web to rest. When revived, the female pulls out the male and eats him.

Males of this species are much smaller than females and do not have much of a chance. Females frequently attack males, but the deaths documented by Foellmer and Fairbairn did not involve any female aggression.

The strategy is consistent with that of other spider species. Male redback black widow spiders, for example, commit suicide by enticing the females to eat them. This allows them to mate for a longer period of time if they are consumed during sex.

Jutta Schneider, a behavioral ecologist at the University of Bonn in Germany, said the surprising fact about Argiope aurantia males is that they "kill themselves, while in other species they have the females do the job for them."

Schneider added, "It is exciting that in each Argiope species studied so far, males are very limited in the number of matings they get — they use each of their two mating organs only once. But the actual mating behavior of males differs between species and so does their way of dying."