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What Type of Spider Kills the Male After They Mate?

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An interesting feature of reproduction among spiders is that many female species cannibalize their mates. Researchers believe this cannibalism has a simple explanation: males who are eaten are smaller than the females and make an easy meal. An exploration of some spider species notorious for this cannibalism supports this and others explanations as does an examination of the much rarer cannibalization of females by males.

Genus Latrodectus

This genus of spiders includes the most notorious of all mate eating spiders: the black widow. In fact, all of the spiders in this genus are collectively known as the “widow spiders” because most of the females occasionally consume the males. Sexual dimorphism is significant in these species with the females being larger than the males. For example, the female black widow's body is approximately 1/2 inch long with the male's body being half that size or less. Australian redback spiders also belong to this genus. Males have adapted to the potential threat by developing two palps (the organs used to inseminate females) so they can mate twice before potentially being devoured.

Wolf Spiders

Female wolf spiders of some species will cannibalize both suitors and mates. Wolf spiders grow large and resemble tarantulas. More than 200 different species have been identified and usually the female is significantly larger than the male, as is the case with the Australian varieties. A study of female wolf spiders found that potential mates were killed in 10 percent of encounters. More interestingly, the researchers discovered a correlation between mate consumption and offspring success. The offspring of females who ate their mates after copulation had a four-time greater chance for surviving the first month of life.

Misconception of Female Mate Consumption

Although mate cannibalism is sometimes viewed as a routine part of spider mating, this cannibalism does not occur in every mating example. Even “widow spiders” do kill their mates after every sexual encounter, one-third of male redback spiders survive the encounter while most black widow cannibalization occurs only occasionally. In a 2008 study of wolf spiders, researchers found that larger males survived nearly every mating encounter while smaller males only survived 20 percent of the time. These findings suggest size does matter when it comes to the risks of spider mating.

Male Cannibalization of Female Mates

In some spider species, males will cannibalize females. Two species of wolf spiders found in Uruguay, for example, consume female mates. Interestingly, in these species the sexual dimorphism favors the males. One such wolf spider species – the Allocosa brasiliensis – was seen by researchers consuming older females while mating with virgin females. In 2005, researchers found male cannibalism in the Argyroneta aquatica species of spiders. Again, males tend to be larger than females in this species - the only species of spider which lives underwater for its entire life. Researchers also noticed that females of the species would flee from larger males who attempted to mate with them.