Thursday, 21 September 2017

Sacrificial virgin spiders let their nieces eat them alive

18 September 2017
Anja Junghanns
By Sandhya Sekar
Habitat: Massive spider webs in southern Africa
It takes a lot to be a good aunt if you’re a velvet spider. In fact, it takes your internal organs. After tending lovingly to your sisters’ eggs and regurgitating food for newborns, it’s time to offer yourself as the main course for the spiderlings to suck you dry.
“[The] spiders literally start feeding on the female while she is alive,” says Trine Bilde at Aarhus University in Denmark. The spiderlings inject enzymes to dissolve her innards and suck out the semi-digested fluids, leaving only the outer shell. “But there is no apparent aggression. It looks as if females are almost inviting spiderlings to feed on them.”
S. dumicola are social spiders that live in large communal nests. Hundreds cooperate to capture prey, defend the nest and take care of the young. The nest is a dense retreat of silk and plant material, with two-dimensional webs to catch prey. Each spider only lives for a year, so can only reproduce once.
In the closely related species S. lineatus, only mated females care for spiderlings. In these spiders, the act of mating seems to cause females to care for other offspring as well as their own – an act called “alloparenting”. However, there are limits: they only let their own spiderlings eat them. Letting your kids eat you is a surprisingly common behaviour known as “matriphagy”.
Eat me!
Bilde and her colleagues wanted to find out whether unmated S. dumicola females also perform alloparenting duties. They bred spiders in the lab and placed them in groups, each with two mated and three virgin females, along with some spiderlings, to observe their behaviour.

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