Intertidal Spiders (Desidae)

The species-poor family Desidae currently comprises just under 330, mostly medium-sized species and is unusual for three reasons. First, the habitat of many Desidae is in the tidal zone of the world’s oceans. Spiders, as emphasized in every spider book, occur (with the exception of one species) only on land. This assessment seems to have overlooked the Desidae, which are very aptly called intertidal spiders. This is because they live on mudflats, a habitat that is only exposed at low tide. Here, they occur as free-hunting spiders. Thanks to their scopulae (adhesive hairs for good climbing on smooth surfaces), they are perfectly adapted to this habitat and catch, for example, small crustaceans. When the sea level rises again at high tide, they retreat into cavities in the ground, between rocks, or in animal structures such as empty barnacle or mussel shells. There, a silk web protects them from the water and provides the spider with an air space.