Sexual cannibalism is very common in some species like the male coin spiders. Black widow and Redback female spiders are famous for slaying their partners soon after mating. The male widow spiders that are considerably smaller in size, are often seen voluntarily offering themselves to be eaten, with a hope that the female will give birth to his offspring. Sometimes, the males reaching out females are mistaken for prey and are killed even before copulation occurs.
Insemination of Young Females with their Sperms
However, in a recent study, researchers have discovered male spiders’ unique behavior to avoid becoming post coital snacks for the females. They noticed that the male redback (L. hasselti) and brown widow spiders (L. geometricus) opt for juvenile female spiders, which have not yet attained maturity. This behavior ensures insemination of young females with their sperms, so that after attaining maturity, produce his offsprings and the male escapes being eaten by them, giving them opportunity to mate more than once.
The co-author of the study, Maydianne Andrade of the University of Toronto Scarborough observed this behavior while conducting unrelated research on two widow spider genus. The research revealed that though in the juvenile stage, the genitals of the females were well developed, but remain sealed. The juvenile female bodies are covered with shell like-exoskeleton. The males of both these species use fangs to cut open the female exoskeleton and enter their genitals to deposit their sperm in the females’ sperm receptacles, called spermathecae.
Live to find another mate
The male spiders carry out this behavior just at the right time, a few days before the final molting, when the genitals are fully matured but not yet exposed. The males are extremely cautious while mating and do not cause any injury to females and has no effect on the juvenile females’ development or fertility.
Such premature advances give males certain advantages. Mating with an immature female gives the male a chances to deposit their sperm in the female spermathecae and plug them, ensuring prevention from other males from replacing his sperms. Plus they don’t get eaten and so can live to find another mate.
Juvenile insemination is not common
The new male technique may sound very safe, but it is not very easy for the male spiders to spot females in the narrow time frame when the female genitals are internally matured but not exposed. Unlike adult females, juveniles do not release any airborne pheromones that can attract males. But still juvenile insemination is not very uncommon as the research team found that nearly a third of female juvenile widow spider are being mated.
Until now, the researchers were aware of only one side of the story where the larger dominant female has all the power, but now the other side of the story is known too. The team is yet to find answer to question as to why the young females do not end up feasting on males; and what is the benefit of such mating for them?