Scorpions are the only arachnid group that has abdominal
stingers, producing toxic venom. The bite of a black widow
spider injects toxic, but seldom deadly venom. Arachnids feed
mostly on insects; many arachnids are predators of agricultural
insect pests.
Ticks and mites number more than 50,000 species. Certain
mite species inhabit the dust in our houses and the follicles
of our eyelashes. These chelicerates live in myriad terrestrial,
marine, and freshwater habitats. Some species are vectors of
Lyme disease and encephalitis. Other mites and ticks are pests
of domestic animals. Mites and ticks feed on vertebrate blood,
invertebrates, fungi, and plants.