The other day, I caught a spider I didn’t recognize — this is not at all uncommon, I’m an amateur trying to learn — and I had to post it on iNaturalist to get it identified. It was a Pirate Spider! I’d never seen one before. If you’re not familiar with pirate spiders, they’ve earned their name: they are predators of spiders that board other spider’s webs and kill the owner and loot her of her life, arrrr.
Pirate spiders are members of the spider group that includes all the “orb weavers” – those that make the prototypical, circular webs we are all familiar with – but they do not make webs.
In fact, they have lost the ability. They can still produce silk, which they use to build egg sacs and wrap prey. But they are anatomically incapable of spinning a web. The number of silk “spigots” on their spinnerets is dramatically small compared to their relatives.
Instead, they invade the webs of other spiders, in a bid to lure and then kill the hapless architect. Gently, they pluck the strings of the web, enticing the host to approach.
Once the host spider has ventured close enough, the pirate makes its move.
First, it encloses its duped prey within its two enormous front legs. These are fringed with massive spines, called “macrosetae”, which they use to trap the host within a prison-like basket.
Then, the final move: the pirate bites its prey and uses its fangs to inject a powerful venom that instantly immobilises it.
I include my photo below the fold.
The diagnostic feature, I take it, is the row of spines all angled in the same direction on the forelegs.