Pyramid ant  (Dorymyrmex insanus)

Dorymyrmex insanus is classified as Vulnerable (VU) on the IUCN Red List (1).

Dorymyrmex insanus is sometimes referred to as the ‘crazy ant’, a name that, along with the scientific name ‘insanus’, refers to its frenzied movements and ability to swarm upon prey and enemies (3). Dorymyrmex insanus has a smooth and shiny body which is light brown to dark brown or blackish-brown in colour (2) (4). It has a pyramid-shaped projection on the first abdominal segment which is diagnostic of all pyramid ants (those belonging to the genus Dorymyrmex) (3). A beard-like structure of hairs under the head of Dorymyrmex insanus, known as the ‘psammophore’, is usually present and is used to carry eggs, seeds and excavate soil around the nest entrance (5) (6). All pyramid ants possess anal glands that produce an odour that has been described as smelling like rotten coconuts (4).

Dorymyrmex insanus is native to the USA and Mexico. Its range extends from northern Mexico and central Texas, north to Kansas and west to southern California (2).

This ant favours hot, open, dry habitats, including deserts (3). Dorymyrmex insanus nests are excavated in a variety of soil types in sunny, open areas (4), sometimes near, or partially under, a large shrub, such as a creosote bush (Larrea tridentate) (3) (7).

Dorymyrmex insanus lives in colonies containing 2,000 to 3,000 individuals (4) in nests excavated in soil. The entrance to a Dorymyrmex insanus nest is a small hole in the ground, marked by a characteristic volcano-like mound of excavated earth measuring up to ten centimetres wide (3) (7).

Within each colony there are three classes or ‘castes’ of ants: males, workers and queens. As in most ant species, the virgin queens (winged females) mate with winged males, and afterwards, the males die while the queen sheds her wings and finds a suitable location to excavate a new nest. Here, the queen lays eggs and cares for the larvae and pupae until they reach maturity. These adults are typically all workers (sterile females) and assist the queen by caring for the next brood, foraging for food and expanding the nest. It is only once the colony is well established that winged virgin queens and males will be produced (8). Dorymyrmex insanus virgin queens and males spend winter in the nest before emerging in June (4), when they commence their search for a mate and a new nest site. A colony will persist as long as the queen is able to produce viable eggs (8).

Dorymyrmex insanus workers (the wingless, sterile females) are very active and opportunistic predators, feeding on a varied diet that includes vertebrate carcasses, termites, flies, beetles, and honeydew (3) (7). The workers form long trails that can be seen moving rapidly over and around objects as they search for food (3). Dorymyrmex insanus has a great tolerance for heat and can forage for food in temperatures that are too high for many other ant species (4).

It is possible that populations of Dorymyrmex insanus may be threatened by the invasion of the Argentine ant (Linepithema humile). The Argentine ant, native to South America but now widespread in temperate and subtropical latitudes around the world, is thought to out-compete Dorymyrmex insanus for food resources (9).

There are no known conservation measures currently in place for Dorymyrmex insanus.

To learn more about the conservation of ants and other insects see:

• The Xerces Society:
  http://www.xerces.org/
• Buglife:
  http://www.buglife.org.uk/