Other ectoparasites found on gills are leeches and, in seawater, larvae of gnathiid isopods. The beak of birds plays a role in removing skin parasites (ectoparasites) such as lice. Water mite larvae act as ectoparasites of water striders. The tricolored bat is the host to several species of endoparasites (internal parasites) and ectoparasites. It is affected by a number of ectoparasites (external parasites) and endoparasites (internal parasites). Parasites can be internal (endoparasites) or external (ectoparasites). Cypermethrin is used in agriculture to control ectoparasites which infest cattle, sheep, and poultry. The labouls include over 2000 species of obligate insect ectoparasites, with cellular thalli. They are wingless and eyeless, as are many other ectoparasites. The Anoplura are all blood-feeding ectoparasites of mammals. Ticks satisfy all of their nutritional requirements as ectoparasites, feeding on a diet of blood. These envelopes screen the sleeping fish from predators and ectoparasites. Anting to get rid of ectoparasites is another hypothesis for anting in songbirds. These are more specialized and are used for defense against predators and larger ectoparasites. Bshary and Grutter found that cleaner wrasse prefers the client tissue mucus over ectoparasites.