One spider that stands out from the eight-legged crowd, due to the fact that it’s rarely found outdoors and doesn’t use silk much, is the spitting spider, Scytodes thoratica.
Where do spitting spiders live?
Spitting spiders are particularly fond of old buildings and museums. It has been suggested that they may well be non-natives imported on construction materials and have since become naturalised in the southern half of the UK. Whatever their origin, they’re a fascinating addition to our more furtive fauna.
I found my first spitting spider by accident: a late-night B-movie and a thirst for an accompanying beer had me heading for the kitchen. I snapped the light on and it immediately caught my eye. I always ‘twitch’ spiders, but this one was different to anything I’d seen before. It was the way the spider was moving that made me do a double-take – it walked with a deliberate, stealthy cat-crawl over the white-washed stone wall.
What do spitting spiders look like?
Those eight legs – spindly and smooth save for a scattering of sensory hairs called trichobothria – were distinctive, as was the colouring of its body, a waxy, jaundiced-yellow speckled with brown.
But it was the unmistakable humped appearance of the cephalothorax (the front portion of a spider’s two main body divisions) that clinched the identification. No other British spider bulges with such intent.
How do spitting spiders hunt?
The hunting strategy of this arachnid puts you in mind of a more vicious Peter Parker. For just as Spiderman, Parker’s superhero alter ego, slings webs to ensnare villains, so our spider relies upon a similar approach to catch its prey, but with one crucial difference: the spitting spider’s webbing isn’t just sticky, it’s venomous.
Why are they called spitting spiders?
They are called spitting spiders because they spit out a sticky venom onto their prey. Protruding from its head are two sacs, one containing a venom, the other a silky glue-like substance. When the spider stumbles into a booklouse or similarly small invertebrate, it contracts the muscles of these sacs. The goo they contain is then forcibly ejected through the tips of the raised chelicerae (the spider’s ‘fangs’).
The attack is fast and deadly accurate: the goo fires from the tips of the chelicerae at a speed of around 30m per second and can pin down a future dinner standing more than 1cm away. It’s almost incredible, given the spider is doing this in the dark by detecting the minuscule vibrations caused by the prey.
The two times I’ve seen spitting spiders hunting, the catch happened so quickly that it didn’t register. One moment there was a spider and a booklouse; the next the booklouse was pinned to the ground under a delicate zig-zag of grey stitches.
The process that produces the zig-zag pattern is even faster than the speed at which the venomous silk is spat out. As the spider lifts its fangs, they vibrate at a rate of 300–1,800Hz, causing the strands of fluid to flick from side to side. The final, beautiful detail is that, upon impact, the strands contract by 50 per cent, tightening the net around the spider’s next meal.
Main image © André Karwath aka Aka, CC BY-SA 2.5 <https://creativecommons.org/licenses/by-sa/2.5>, via Wikimedia Commons
