|Image: James Niland|
Or so it was once thought...
|Image: Miguel Pérez|
The stabilimentum is a rather decorative structure that many spiders build into the centre of their webs. They tend to look pretty darn snazzy! From lightning strikes and spirals of lightning to circular platforms made of pure lightning. Pure Lightning! Or silk. Maybe.
Video: Theresa Wiltrout
Yeah, probably silk. Ribbons of soft, fluffy silk.
Though some spiders, not least those of the genus Cyclosa, will use corpses and detritus to gussy up their web. Where on earth would spiders be without their decorative corpses? Some kind of insect heaven, I guess. Where the spiders are herbivores and pesticide is sweet, sweet nectar.
|Image: 潘立傑 LiChieh Pan|
But what's it all for, these strange decorations? Apart from being an art installation, I mean.
As you can tell from the name, stabilimentum, it was initially thought that they provide extra stability to the web. It's a reasonable guess, many stabilimenta designs even look a lot like truss bridges. However, this particular hypothesis has been entirely dismissed. Partly because of all the spiders who don't build stabilimenta.
|Image: Jessica Lucia|
Another possibility is practically the complete opposite. Spiders go to a whole lot of effort building their web. They'd rather not lose it to some galumphing oaf like an oblivious bird or other animal. So perhaps the stabilimentum serves as a kind of warning, a sign which means "beware the invisible object".
|Image: Patrick Randall|
Other ideas are that it can be used as a kind of sun shield to help with thermoregulation, or it's a platform for when they moult their exoskeleton or it guides male spiders to a waiting female, or it makes spiders look BIGGER so that hungry lizards think twice...
|Image: Greg Lasley|
All of which makes it seem that there may well be more than one purpose for a stabilimentum. For example, perhaps they really do attract prey and a well-fed spider simply doesn't need one. At the same time, maybe 'warning' birds of the presence of a spider web is actually more like 'advertising' to birds the presence of a tasty spider. Or perhaps, it's the complete opposite, and decorations stop birds from flying into the web but at the same time reduce the number of insects that fly into it, too.
PHEW! It's amazing to think that one of the prettiest and most conspicuous aspects of spider life remains so mysterious. I guess it shouldn't be so surprising that they have a few tricks up their sleeve. After all, they have a lot of sleeves. Or trouser legs.