Some spiders, like Black Widows, eat their mates after sex. New research shows that male orb-web spiders make this sacrifice for the health of their offspring. In the orb-web spider Argiope bruennichi, it’s a common practice. The female typically tries to wrap up the male at the start of mating so she can eat him even during sex.
In this study, only about 30 percent of the males survive their first mating, but by when the female feeds on them, it makes the sex act last longer, making it more likely they will inseminate their mate. Half of the survivors go on to find a second mate, while the others are more daring and try for the same female again. They are limited to two copulations because of the male’s anatomy.
They had thought that this practice was a “paternal investment into their own offspring, and they provide females with nutrients.” To see if this was the case, they divided the female orb-web spiders into three groups, allowing them to mate with one, two, or three males. Half of each group of females was allowed to eat their mates. For the others, the researchers saved the male. Afterward, they looked at each female’s eggs and offspring. The eggs were counted and weighed and they looked at how many offspring survived simulated cold-weather scenarios and a 20-week period of starvation.
There was no nutritional bonus, however, they found that the offspring was healthier, survived better, and had larger eggs.