In dark fishing spiders, males’ postmating nap is permanent

Species prepares for two pairings but goes into a fatal coma after a single encounter

FIRST AND ONLY A male dark fishing spider (right) self-destructs during his first and only mating experience. He spontaneously collapses into a dead-spider position though his sperm-delivery organ still connects him with a female.

S.K. Schwartz

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Once is apparently enough for male dark fishing spiders. After delivering only half of their available sperm to a single female, males curl up and wait for death.

In the considerable annals of spider sex ending badly, male Dolomedes tenebrosus suffer a fate not described before, says behavioral ecologist Steven K. Schwartz of the University of Nebraska-Lincoln. Males of this widespread North American species prepare sperm for two matings but spontaneously fall into a spidery version of a coma during the first one. Their legs crumple and their bodies hang terminally motionless without any sign of the female having injured them, Schwartz and his colleagues report June 18 in Biology Letters.

Male spiders deliver sperm via a pair of boxing-glove shaped projections, or pedipalps. Male dark fishing spiders load both pedipalps with sperm, but in lab and outdoor matings, males used only one before curling into a deathlike posture. Even when protected from any female attack, males’ hearts stopped beating about two hours after mating, Schwartz says.

If females eat the inert male, his death may gain him especially abundant or healthy offspring, Schwartz speculates. Or a recently fed female may be less likely to mate with the next suitor that comes along.

As dark male fishing spiders prepare to mate, the male (smaller than the female) rocks the female’s body. When he finally inserts one of his sperm-delivery organs into one of her reproductive openings, he suddenly collapses. He no longer responds when researchers pick up or poke at him.
Credit: S.K. Schwartz

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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