The fire ant Solenopsis invicta is a species that is expanding its range around the world and is one of the species that is most often involved in medical emergencies. The species is aggressive and has a painful sting. A person typically encounters fire ants by inadvertently stepping into one of their mounds, which causes the ants to swarm up the person's legs, attacking en masse. The ants respond to pheromones that are released by the first ant to attack. The ants then swarm and immediately sting when any movement is sensed. People who are sensitive to the venom can die of anaphylaxis. In a survey of 29,300 physicians in the United States of America (in 1989), reports of 83 fatalities were obtained. Some fire ant attacks on humans confined to beds have also been noted it has been noted that fire ants can be a particular threat in medical facilities in some locations since they can have nesting colonies inside human habitations.
Argentine ant, Linepithema humile Argentina, Southern Europe, Southern USA, California Very small, attack mostly other ants. The main supercolony (Italy, Atlantic coast of Spain) is said to be the largest cooperating ant population in the World.
Pharaoh ant, Monomorium pharaonis Worldwide
Bulldog ants, genus Myrmecia are found in Australia and belong to the ant subfamily Myrmeciinae, and are among the most primitive extant ants. All but one of the sixty or so species are found in Australia. This species is known to cause some fatalities in sensitive humans.
Legionnaire ants are most interesting southern boreal obligate dulotes of the Formicinae subfamily. Their host is, like a similar convergent species, Formica sanguinea, ants of the Formica fusca group. Although absent from the British Isles, Polyergus rufescens is present on the continent, and many observations of its behaviour were made by Auguste-Henri Forel.
Like the unrelated British-found parasite to Tetramorium caespitum, Strongylodus testaceus (first discovered in Britain by Horace Donisthorpe), the legionnaire ants display greatly adapted, strongly falcate mandibles, which they use for piercing the heads of F. fusca et al. during raids.
Yellow crazy ant, Anoplolepis gracilipes Christmas Island They kill red crabs on Christmas Island, and generally destroy the ecosystem for the other 17 species of terrestrial crab found there, including the largest terrestrial invertebrate in the known world (the coconut crab).
Driver ants, genus Dorylus The Old world, esp. West Africa and the Congo Basin Unlike the army ants of the New World, Old World army ants have a functional sting, but rarely use it; this is more than compensated for by their razor-sharp, falcate mandibles. Dorylus spp. colonies also reach larger sizes than Eciton. The Siafu ants on Mount Meru in Tanzania were implicated in the death of a missing tourist to the Congo.