Passive dispersal in arachnids

Some arachnids (spiders, mites and pseudoscorpions) are able to use both active and passive dispersal. The best-known passive dispersal method in arachnids is called eballooningi and starts with etiptoe behaviouri. Using threads of silk, spiders can move from place to place with air currents. Usually the spider aeronauts are small, but sometimes larger ones can also be transported in this way. Some mites spread passively also by using threads of silk, or use their own body as a carrying surface. A great number of mite species intentionally use other animals (e.g. insects) as carriers, and this phenomenon is known as phoresy. Similarly, pseudoscorpions sometimes infest insects. The most probable reasons that may cause passive dispersal are: overpopulation, changeable physical conditions, and ecocatastrophe. Passive dispersal is one of the major ways of colonization of new areas and habitats, which extends geographical ranges of species. The oldest traces of passive dispersal come from the Tertiary period, but it is thought to have existed also in the late Mesozoic. From an evolutionary point of view, the most interesting is the phoront-host relationship, as a result of co-evolution (e.g. Rhinoseius mites with hummingbirds).