DARWIN’S BARK SPIDER
Lucy Cooke on a ruthless and highly emasculating huntress
SEDUCTION IS ALWAYS AN awkward game. Stakes are high, as is the suitor’s vulnerability. But when the object of your desire is a ferocious predator that eats animals that look like you for breakfast, dating becomes a dance with death.
This is particularly true of Darwin’s bark spider (Caerostris darwini). The female is Goliath to her mate’s David; about 14 times his weight. To seduce her, the male must gingerly traverse her enormous web – a succession of tripwires designed to sense the slightest vibration – and copulate, all without triggering her attacking instinct.
The big spider in the middle of a web is, in fact, always female. Males are little more than walking sacs of sperm without the time, or need, for hunting. Their webs and weaponry are puny in comparison – females have the longest fangs and most potent venom. They also live longer and grow larger in order to nourish as many eggs as possible. To do so they’ve become nature’s greatest (and deadliest) engineers.
Darwin’s bark spider is a world record holder. Her silk is the toughest biological material ever studied – twice as strong as any other spider’s and 10 times tougher than Kevlar. She uses it to spin the biggest webs ever recorded: one orb measured 2.8m2, with anchor lines over 24m long. She casts over streams, with the web resting above water where it can trap flying insects as they hatch. One was found to contain 32 mayflies – their short life rendered even shorter by this extraordinary hunter.
She’s not averse to catching and eating her sexual suitors before, during or after sex. Studies have shown that cannibalism provides the female with superior sustenance, as the nutrients derived from the male are effectively tailor-made for making baby spiders. Sexual cannibalism is thus the ultimate act of paternal care, as long as the munched male is actually the father.
Darwin’s bark spider females are promiscuous, so the male must not only stay alive long enough to inseminate, he must also prevent her from mating with others. To achieve this end, evolution has equipped him with some kinky solutions: bondage and genital mutilation.
First, he times his approach when the female is vulnerable – just after she’s moulted, her exoskeleton still soft. He then binds her legs with his silk so she can’t grab him. Next, he drools on her genital slits. This behaviour, not found in other spiders, may be an attempt to seduce her by signalling mate quality, or to digest previous suitors’ sperm. After insemination, he ensures no other spiders follow suit by plugging the female with his own chewed off genitals. An emasculating finale that secures his legacy, if not his life.
Catch up with Lucy’s BBC Radio Four three-part series Political Animals
Lucy is a broadcaster, zoologist and author of Bitch: A Revolutionary Guide to Sex, Evolution and the Female Animal.