Ticks of domestic animals directly cause poor health and loss of production to their hosts. Ticks also transmit numerous kinds of viruses, bacteria, and protozoa between domestic animals. These microbes cause diseases which can be severely debilitating or fatal to domestic animals, and may also affect humans. Ticks are especially important to domestic animals in tropical and subtropical countries, where the warm climate enables many species to flourish. Also, the large populations of wild animals in warm countries provide a reservoir of ticks and infective microbes that spread to domestic animals. Farmers of livestock animals use many methods to control ticks, and related treatments are used to reduce infestation of companion animals. Variety of ticks affecting domestic animals Ticks are invertebrate animals in the phylum Arthropoda, and are related to spiders. Ticks are in the subclass Acari, which consists of many orders of mites and one tick order, the Ixodida. Some mites are parasitic, but all ticks are parasitic feeders. Ticks pierce the skin of their hosts with specialized mouthparts to suck blood, and they survive exclusively by this obligate method of feeding. Some species of mites may be mistaken for larval ticks at infestations on animal hosts, but their feeding mechanisms are distinctive. All ticks have an incomplete metamorphosis: after hatching from the egg, a series of similar stages (instars) develops from a six-legged larva, to eight-legged nymph, and then a sexually developed, eight-legged adult. Between each stage is a molt (ecdysis), which enables the developing tick to expand within a new external skeleton. Ticks are grouped in three families, of which two have genera of importance to domestic animals, as follows. The family Argasidae contains the important genera Argas, Ornithodoros, and Otobius. These genera are known as soft ticks because their outer body surfaces lack hard plates. The family Ixodidae contains 14 genera, including Amblyomma, Dermacentor, Haemaphysalis, Hyalomma, Ixodes, Margaropus, and Rhipicephalus. Also, the important boophilid ticks, formerly of the genus Boophilus, are now classified as a subgenus within the genus Rhipicephalus. These genera are known as hard ticks because their outer surfaces have hard plates. Within these genera are, very roughly, 100 species of importance to domestic animals. Some of these species are also important to humans. The only countries that do not have some kind of problem with ticks on domestic animals are those that are permanently cold. An outline classification of the Acari, including the