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also much less common than other styles of consuming close relatives (as in sibling by sibling, or mothers by offspring; see essay 10 in Ever Since Darwin and essay 6 in The Panda’s Thumb ). Documented examples exist only for arthropods (insects and their kin), and only thirty species or so have been implicated (though the phenomenon may be quite common in spiders). They cite three examples as best cases.
The female praying mantis ( Mantis religiosa , and several related species) will attack anything smaller than itself that moves. Since males are smaller than females in almost all insects, and since mating requires proximity, male mantises become a premier target. In his classic paper of 1935 (see bibliography), K. Roeder writes: “All accounts agree as to the ferocity of the female, and her tendency to capture and devour the male at any time, whether it be during the courtship or after copulation…. The female may seize and eat the male as she would any other insect.”
      A male therefore approaches mating with the punch line of that terrible old joke about how porcupines do it: very carefully. He creeps up slowly, trying at all costs to keep out of the female’s sight line. If the female turns in his direction, he freezes—for mantises ignore anything that doesn’t move. Roeder writes: “So extreme is this immobility that if a male is in the act of raising a leg when first the female is detected, it will be kept poised in the air for some time, and many curious positions may be observed.” Thus, the male continues to approach like a child playing the street game of “red light”—drawing near while his adversary and potential mate averts her eyes, freezing instantly when she looks around (although the penalty for apprehended motion is death, not a return to the starting line). If the male succeeds in creeping up within springing distance, he makes a fateful leap to the female’s back. If he misses, he’s mantis fodder; if he succeeds, he achieves the Darwinian summum bonum of potential representation in the next generation. After mating, he falls off as far away as he can and then skedaddles with dispatch.
      So far, the story sounds little like a tale of active male conspiracy in his own demise—the requirement, please remember, for an argument that males are directly selected for sexual cannibalism. Perhaps males are simply trying their darndest to get away, but don’t always make it. The strong argument inheres in that great curiosity mentioned at the outset of this essay: decapitated males perform better sexually than their intact brothers. Roeder has even discovered the neurological basis for this peculiar situation. Much of insect behavior is “hard wired,” so unlike the flexibility of our own actions (and a primary reason why sociobiological models for ants work so poorly for humans). Copulatory movements are controlled by nerves in the last abdominal ganglion (near the back end). Since it would be inconsistent with normal function (and unseemly as well) for males to perform these copulatory motions continually, they are suppressed by inhibitory centers located in the subesophageal ganglion (near the head). When a female eats her mate’s head, she ingests the subesophageal ganglion, and nothing remains to inhibit copulatory movements. What remains of the male now operates as a nonstop mating machine. It will try to mount anything—pencils, for example—of even vaguely appropriate size or shape. Often it finds the female and succeeds in making of its coming death the Darwinian antithesis of what Socrates called “a state of nothingness.”
A hungry female black widow spider is also a formidable eating machine, and courting males must exercise great circumspection. On entering a female’s web, the male taps and tweaks some of her silk lines. If the female charges, the male either beats a hasty retreat or sails quickly away on his own gossamer. If the female does not respond, the