Bolas Spider

Image: Kenneth F. Haynes and Kenneth V. Yeargan

It's always a little creepy when a spider acquires an unusual skill. So let's get creepy!

Today we take a look at the Bolas Spider, 66 species of tiny, nocturnal spiders from Africa, the Americas and Southeast Asia.

They really are puny, with females reaching 1.5 cm long and males just 2 mm. They also have that incredibly chunky, rotund abdomen so common in tiny web spinners who have no need to spend their time running around the place.

By day, many Bolas Spiders mimic other things that don't get around much, like snail shells and bird droppings. The bird droppings ones even produce a stink when disturbed, which is extremely rare among spiders. Presumably it's quite common in bird droppings, but I don't often get close enough for a sniff.

Come the night, hunting begins.

The Bolas Spider dangles a glob of glue at the end of a line of silk. This is where they get their name from, the bolas being a really old weapon for capturing animals. Of course, the spider doesn't use it for catching cattle or llamas, we're not wandering around in someone's nightmare after all. No, they use it on moths.

If you ever caught a moth in your hand, you probably experienced a dusting from their wings. Moth and butterfly wings are covered in tiny scales that provide them with all that colouration. In moths, they often come in every conceivable shade of brown. The scales fall off readily, a slight problem for our hands but a big problem for spiders who find moths escape their sticky webs leaving nothing but scales behind.

The Bolas Spider has a solution. Their bolas is covered in watery stuff that flows through the scales so that glue in the middle can stick onto the actual moth underneath. It's evil genius stuff! But it's even worse because Bolas Spiders release pheromones to attract excited male moths hoping to get lucky with a nice female. They get eaten instead. Still by a female though, so they were half right!

Image: Arthur Chapman via Flickr
Eggs sacs of the Bolas Spider

Male Bolas Spiders are simply too tiny to use their own bolas. Instead, they stick their legs out from the side of a leaf and grab hold of tiny flies. This is also what the babies do, so it may be the case that whatever tiny bolas they could produce would simply dry up too quickly.

Even the female eats her own bolas if she doesn't catch anything within about half an hour. Nevertheless, her strategy is so successful that she'll catch one or two moths every night, sometimes more. Add in the venomous bite and she can have a go at prey a fair bit bigger than herself.

Not only is this an amazing example of how venom and sticky silk have enabled spiders to become such impressively successful arachnids, it also ensures that massive, spherical abdomen of hers is well fed.