Ground spiders use super-tough silk to hunt creatures twice their size
Fantastically strong piriform silk is the secret weapon of Gnaphosidae spiders that actively hunt much larger arachnids, writes Andrew Masterson.
Here’s a good piece of advice for arachnids, made apparent by research published in the Journal of Experimental Biology: do not, on any account, pick a fight with a flat-bellied ground spider that goes by the name of Drassodex heeri.
Even if you’re twice as a big, you’ll lose. There’s no real survival value in running away, either. Chances are, if it sees you, it will take the initiative and attack.
Attacking is what Drassodex heeri does: it’s a hunting spider of the family Gnaphosidae, a collection of 2200 species that eschew the standard arachnid approach of waiting in a web until something tasty blunders into it. Instead, they go out and hunt prey, which often includes other, larger spiders.
This behavior has long fascinated scientists because, on the surface, it seems like a peculiar evolutionary adaptation. Actively hunting large, well-armed prey carries with it a considerable risk of injury.
The fact that the strategy clearly works for the ground spiders prompted an investigation by a group of researchers from Germany, Australia, the Czech Republic and Poland to discover why.
The findings reveal that the ground spiders produce large amounts of extra-strong silk from rear-end dispensers – known as spigots – that are modified to ensure they don’t clog up in the heat of battle.
“Hunting spiders that feed on dangerous prey like ants or other spiders are an extreme example of dangerous feeding, risking their own life over a meal,” writes the team, which is led by Jonas Wolff, a behavioural ecologist from Australia’s Macquarie University.
The researchers studied the hunting techniques of Drassodex heeri by, essentially, setting one up in a series of pitched battles against other spider species and filming the results.
The key to success, they observed, lay in the production of type of silk known as piriform. Most other species of spiders produce only small amounts of piriform silk, which is super-tough, comparatively rigid, and used to anchor webs to supporting structures.
Ground spiders, however, produce it in abundance, through modified spigots, using it to, first, anchor itself to the ground as soon as it pounces on its prey, and then wrapping it around its victim’s legs, rapidly immobilising it.
Ground spider piriform differs from that of most other species not only in quantity but also in quality. Wolff and colleagues found it comprised an elastic central fibre encased in two layers of glue covered in nano-tendrils. This, the team writes, makes it “very stretchy and tough, which is an outstanding feat for a functional glue”.
Indeed, that turns out to be something of an understatement. In further analysis the team determine that the stickiness and elasticity of the piriform silk mean it can withstand shear forces a stunning 750 times greater than those endured by most artificial glues.
All of which produces another important take-home message for even really, really big spiders: if you find yourself tied up by Drassodex heeri, you are absolutely going to stay that way.