Sexual cannibalism is common among most predatory species of mantises in captivity. It has sometimes been observed in the field, where about a quarter of male-female encounters results in the males being eaten by the female. Around 90% of the predatory species of mantises participate in sexual cannibalism. Adult males typically outnumber females at first, but their numbers may be fairly equivalent later in the adult stage, possibly because females selectively eat the smaller males.In Tenodera sinensis, 83% of males escape cannibalism after an encounter with a female, but since multiple matings occur, the probability of a male’s being cannibalized increases cumulatively.
The female may begin feeding by biting off the male’s head (as they do with regular prey), and if mating has begun, the male’s movements may become even more vigorous in its delivery of sperm. Early researchers thought that because copulatory movement is controlled by a ganglion in the abdomen, not the head, removal of the male’s head was a reproductive strategy by females to enhance fertilization while obtaining sustenance. Later, this behavior appeared to be an artifact of intrusive laboratory observation. Whether the behavior is natural in the field or also the result of distractions caused by the human observer remains controversial. Mantises are highly visual organisms and notice any disturbance in the laboratory or field, such as bright lights or moving scientists. Chinese mantises that had been fed ad libitum(so that they were not hungry) actually displayed elaborate courtship behavior when left undisturbed. The male engages the female in a courtship dance, to change her interest from feeding to mating. Under such circumstances, the female has been known to respond with a defensive deimatic display by flashing the colored eyespots on the inside of her front legs.
The reason for sexual cannibalism has been debated; some consider that submissive males gain a selective advantage by producing offspring. This theory is supported by a quantifiable increase in the duration of copulation among males which are cannibalized, in some cases doubling both the duration and the chance of fertilization. This is contrasted by a study where males were seen to approach hungry females with more caution, and were shown to remain mounted on hungry females for a longer time, indicating that males which actively avoid cannibalism may mate with multiple females. The same study also found that hungry females generally attracted fewer males than those that were well fed. The act of dismounting after copulation is dangerous for males, for at this time, females most frequently cannibalize their mates. An increase in mounting duration appears to indicate that males wait for an opportune time to dismount when the female is hungry, so is likely to cannibalize her mate.
By Renee Zhan ’16