Male spiders who get eaten after sex choose mating partners carefully, study says

Male spiders who are likely to be eaten by their partner after sex are significantly more “choosey” when selecting a mate than the females, a new study has found.

In many species, the males tend to sleep around to maximise their chances of having children as they have almost abundant sperm. Females often only have a limited amount of eggs and so are usually a bit pickier about who they have sex with.

However researchers suspected that when the males were likely to only have one chance to pass on their genes – due to the high risk of death that the academics described as a form of enforced "monogamy" – they might be a little more discerning.

They set out to test their theory by putting colonial orb-weaving spiders, Cyrtophora citricola, in a room together and waiting to see what happened.

A paper in the Plos One journal about their findings, called Coy Males and Seductive Females in the Sexually Cannibalistic Colonial Spider, described a typical sexual encounter between two spiders.

The female approaches the tiny male until she is about a centimetre away. The male then dashes in and “inserts his pedipalp (the male organ) into the genital opening of the female”.

“The female bites the abdomen of the male while the pedipalp is still attached. The female pulls the male towards her mouthparts, and the pedipalp detaches. Copulation usually only lasts a few seconds,” it added.

The results of the study bore out the theory that males were the choosier of the two.

Researcher Eric Yip, of Ben-Gurion University of the Negev, Israel, said: “We found that males prefer to court and mate with younger, fatter, and therefore potentially more fecund females.”

The females on the other hand exhibited “no mate choice related to male feeding or age”, the paper said.

Of the 80 pairs of spiders that courted, 32 had sex within 30 minutes and 21 of the males were killed and eaten.

Seventeen males had sex once, four managed to do it twice. The 11 male survivors just had sex once. The females were less likely to eat poorly fed males.

The paper said that "post-copulatory cannibalism ... enforces monogamy in most males".

It added that the males may be inadvertently increasing their chances of being eaten by breeding with bigger females.

“These findings suggest a co-evolutionary cycle: cannibalism by females led to mate choice by males, which may, in turn, select for more aggressively courting females,” it added.