Sexual Cannibalism

In fishing spiders, sex is violent. Males are often attacked by females during sex, and if killed, they’re promptly eaten1. There is little a male spider can do in defense, as females often exceed 14-times their mass2 in an intimidating display of gender size-dimorphism. This is equivalent to your “better half” having about 2,600 pounds on you.

Females of the raft spider (D. fimbriatus) are especially aggressive, attacking 75% of males during courtship1,3, and in the six-spotted fishing spider (D. triton) precopulatory predation of males can reach 30%4. While to most these are lousy odds, the directive for reproduction in these species is so great that death is an acceptable outcome.

In the dark fishing spider (D. tenebrosus), males die “in the saddle”. This occurs shortly after copulation and is claimed to be due to the mutilation of their genitals2,5. Death can be so sudden, as to leave the spider dangling from their mate.

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1. Arnqvist and Henriksson 1997. Sexual cannibalism in the fishing spider and a model for the evolution of sexual cannibalism based on genetic constraints. Evolutionary Ecology, 11: 255-273.

2. Schwartz et al. 2013. Spontaneous male death and monogyny in the dark fishing spider. Biology Letters, 9: 20130113.

3. Johnson 2000. Sexual cannibalism in fishing spiders (Dolomedes triton): an evaluation of two explanations for female aggression towards potential mates. Animal Behavior, 61: 905-914.

4. Johnson 2005. The role of body size in mating interactions of the sexually cannibalistic fishing spider Dolomedes triton. Ethology, 111(1): 51-61.

5. Schwartz et al. 2014. Obligate male death and sexual cannibalism in dark fishing spiders. Animal Behavior, 93: 151-156.       

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