Anton Gilson, of Balclutha Primary School, asks :-

Can spiders climb?

Cor Vink, an entomologist with the Biosecurity Group at AgResearch and the Adjunct Curator of Spiders at the Entomology Research Museum at Lincoln University, responded.

Yes, spiders are very good at climbing. They are helped by claws at the end of each leg that can hook into very small cracks in surfaces, which are only visible with a microscope. Some spiders are even better climbers as they have dense tufts of hair, called scopulae, under their claws. In some spiders the entire bottom surface of their last leg segments (metatarsus and tarsus) can be covered by scopula hairs.

Spiders that have scopulae on their feet can easily walk on smooth surfaces, such as glass. The end of each scopula hair splits into thousands bristles. This means that a spider with scopuale has many thousands of microscopic contact points that stick to extremely thin water films that are present on smooth surfaces.

Sometimes people find a spider stuck in a bath as they can’t climb up out. These are web building spiders that only have claws at the end of their legs. The bath surface is too smooth for their claws to grip. Spiders with scopuale, usually species that do not hunt using webs, could easily climb out. It is a myth that spiders found trapped in baths come up through the plughole; they have just been wandering along and happen to have fallen into the bath and can’t climb out.

The climbing ability of spiders is also helped by the fact that many of them produce a silk dragline. This is stuck to the surface every now and then as the spider walks along. If it falls off something it can then pull itself back up using its dragline.