Acarids

Acarids, or acari, are a diverse group of arachnids comprising the mites and ticks. They occupy a wide range of habitats and include tens of thousands of described species, found from soil and leaf litter to freshwater, marine environments, and animal bodies. A defining feature is a body typically divided into a gnathosoma (capitulum) bearing the mouthparts and a generally unsegmented idiosoma, with eight legs in adults. Larvae usually have six legs, while nymphs and adults have four pairs.

Ecology and life cycle: Acarids exhibit varied lifestyles, including free-living detritivores, herbivores, predators, and ectoparasites. Ticks are largely hematophagous parasites of vertebrates, feeding in punctuated bouts; mites likewise show a range of habits from predation to scavenging and plant feeding. Reproduction is typically sexual, with complex life cycles that may include multiple larval and nymphal stages before reaching adulthood. Some lineages show parthenogenesis or host-dependent development.

Ecology and impact: In agriculture and stored products, acari resemble pests such as spider mites (Tetranychidae) that damage crops, and storage mites like Acarus siro and Tyrophagus putrescentiae that affect food and feed. Beneficial mites, including Phytoseiulus and other predatory species, are used in biological control. In medicine and veterinary science, mites such as Sarcoptes scabiei and Demodex spp. can cause disease or allergic responses in humans and animals. Ticks, including hard ticks (Ixodidae) and soft ticks (Argasidae), are notable vectors of diseases such as Lyme borreliosis, babesiosis, and rickettsial infections.

Taxonomy: Acari is commonly treated as a subclass or infraclass within Arachnida, divided into two major clades: Acariformes and Parasitiformes. Ticks are placed in Parasitiformes (with Ixodida and related groups).