Female black-widow spiders and praying mantis most often eat their partners after sex. Now, a new study has found that this creepy cannibalism may be meant for having healthier babies.
Researchers at the University of Hamburg in Germany found that male orb-web spiders make this ultimate evolutionary sacrifice for the good health of his offspring.
Sexual cannibalism is the act of one partner eating the other after sex. In the orb-web spider Argiope bruennichi, the female tries to grab and wrap up the male at the onset of mating so she can snack on him during sex.
In the lab, the researchers found that only about 30 per cent of the males survived their first mating, but by letting the female gnaw on them, the males prolonged their sex, making it more likely they will inseminate their partner.
Of the survivors, half go on to find a second mate while the others try again for the same female, researchers said. “Two main hypotheses explain the evolution of sexual cannibalism,” study researcher Klaas Welke told LiveScience.
The males might be offering themselves up “to gain access to mating opportunities and to prolong their mating duration.” Or, Welke said, it could be a “paternal investment into their own offspring, and they provide females with nutrients”. In the case of the orb-web spider, males tend to be much smaller than their mates; they’re only one-tenth as heavy, and researchers weren’t sure how much nutritional benefit the females can gain from such pipsqueak partners. “Our findings suggest a paternal investment of males into their offspring,” Welke said.
“Sexual cannibalism may increase male reproductive success and may be very beneficial in a species with a high paternity insurance and a low rate of polyandry as found in Argiope bruennichi.”