A sticky case of eight-legged housework

View Images

Tear off a piece of sticky tape press it down on a nearby surface and pull it off. You’ll find a thin layer of dirt comes off with it. Rinse, and repeat. Congratulations –you’ve just had a taste of housework, spider-mite-style. The spider mite Stigmaeopsis longus is a sociable critter that works together to build silken nests on the undersides of leaves. In these enclosed spaces, hygiene is paramount. For example, the colony’s members all use a toilet at the entrance of the nest, never defecating inside. They’re also fastidious cleaners and Miki Kanazawa from Hokkaido University has found that they scrub using the same substance that they build their homes with: silk.

She sprinkled small grains of red sand into one of the nests and filmed the females as they went about their chores. Each one pressed her mouths onto one side of the leaf, secreted a drop of silk and walked to the other side, dragging a thread in her steps. She repeated this again and again until, eventually, all the red grains were trapped in a sticky mass on the nest’s ceiling.

The females do exactly the same thing to build their nests in the first place, but Kanazawa found that they did it more often, the more grains she sprinkled into the nest. If the floor is dirtier, the mites weave more silk, confirming that this action is about cleaning as well as construction. It’s a necessary act because the floor of the nest is where the precious eggs sit. By keeping them clean, the females ensure that they will survive. To demonstrate how important this is, Kanazawa removed females from some wild nests. She found that the eggs were half as likely to survive, even if she prevented any predators for attacking them.

Reference: Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2010.1761