Dorymyrmex insanus

One of a number of species throughout that world that have earned their common name, crazy ant, from their noticeably frenetic foraging-activity. Among other species given this moniker D. insanus has the distinction of bearing a latin name that matches its common name.

Identification
Dorymyrmex insanus is one of a confusing tangle of western Dorymyrmex forms that are in need of taxonomic revision. The species of southwestern North America have been shifted between different genera and species names numerous times over the past 100 + years. Snelling (1995) nicely summed up the plethora of problems with insanus: "No North American ant has been cursed with such a singularly unfortunate taxonomic history as that described by Buckley (1866) as Formica insana."

Fisher and Cover (2007) state "In all Dorymyrmex, the propodeum has a single, more or less vertical tooth, or "cone," at the junction of the dorsal and posterior faces." If you find a worker ant within the confines of the Colorado Plateau with this morphology you have collected a Dorymyrmex species. If the workers possess a black gaster and light colored (various shades of yellow- red) head and mesosoma, you have collected Dorymyrmex bicolor. If the workers are concolorous brown or gray your best solution, pending a revision of the group, may be to provisionally assign it the name insanus.

Cuezzo and Guerrero (2011) provided the following diagnosis but its accuracy is questionable until a more thorough revision of the Dorymyrmex is completed: Worker Medium brown to dark. Head longer than wide, lateral sides parallel and slightly convex. Posterior margin of head with a weak median emargination. Pronotum with 0–2 erect setae. Pro-mesonotum slightly convex with a weak subangle behind, forming a feeble tubercle in the same line of propodeum in profile. Queen Maximum cephalic width at the level of compound eyes, weakly narrow behind. Male Dark brown to black. Maximum head width after level of eyes. Posterior margin of head feebly concave in the middle; only three teeth present on the masticatory margin of the mandible. Forewing with no discoidal nor cubital cells.

Distribution based on Regional Taxon Lists
Nearctic Region: United States. Neotropical Region: Brazil, Colombia, Costa Rica, Cuba, El Salvador, Greater Antilles, Guatemala, Honduras, Mexico, Panama, Paraguay, Venezuela.

Range SW United States and N Mexico. Difficulty in delimiting the various forms in this group leads to some ambiguity concerning its distribution.

Biology
These ants, like all North American Dorymyrmex, thrive in hot, open xeric habitats. Workers are opportunistic predators that can quickly recruit many individuals to newly discovered food. Their diet is quite varied. Foragers will readily imbibe honeydew, or any nutritious liquids they encounter, but will also feed on vertebrate carcasses.

Nesting and Foraging Behavior
A number of factors help make these ants a conspicuous part of the southwestern U.S. ant fauna. Nests occur in open ground or in sites with a low profile vegetative ground cover. Their ability to thrive in hot, open dry areas allows them to also do well in disturbed sites. This in turn puts them into direct contact with anyone that spends time outside, be it out in the desert or in heavily settled areas, in the southwest. Their ground nest entrances are small holes in the ground that would be relatively inconspicuous except for the small crater mounds (up to ~ 10 cm in diameter) of soil that surround them. These mounds are made all the more obvious by their tendency to occur in clusters.

In Colombia, Dorymyrmex insanus is commonly found in lowlands. This species nests close to the sea level (75m.) in anthropic sub-xerophytic deciduous forests and in temporal cultivated areas. Some populations are restricted to arid and open areas of central Colombia, between 400 and 700 m, where small herbs cover the ground.

Workers tend to be quite active and tolerate heat better than most species that they co-occur with - although they will stop foraging during the most intense heat of the day during the warmest times of the year. Foragers can form long foraging trails that contain many individuals. These streams of undulating ants flow over, under or around objects that are in the path of such a trail. While individuals workers are small, their dark coloration often contrasts with the lighter soils where they make their nests. Quick movements, foraging trails full of workers, creating small but often conspicuous soil mounds, and an ability to be out in force during hot, sunny days when most ants remain in their nests all make Dorymyrmex insanus a noticeable ant.

Conservation Status
Cuezzo and Guerrero (2011) - D. insanus was considered as a vulnerable species by de IUNC Red List as fitting the “D2” criteria of the vulnerable (VU) category in the “1994 Categories & Criteria,” meaning the population has an acute restriction in its area of occupancy (typically less than 100 km2) or in the number of locations (typically less than five). With the distributional data provided here, this species can be considered to exceed the above criteria and, therefore, should be removed from the list of endangered species.

Castes

 * Worker

Nomenclature

 *  insanus. Formica insana Buckley, 1866: 165 (w.q.) U.S.A. Cuezzo & Guerrero, 2011: 18 (m.). Combination in Dorymyrmex: McCook, 1879: 185; in D. (Conomyrma): Smith, M.R. 1951a: 837; in Conomyrma: Snelling, R.R. 1973b: 4; in Dorymyrmex: Shattuck, 1992c: 85. Junior synonym of pyramicus: Mayr, 1886d: 433; Wheeler, W.M. 1902f: 22. Revived from synonymy as subspecies of pyramicus: Santschi, 1920d: 381. Junior synonym of pyramicus: Creighton, 1950a: 348. Revived from synonymy as species: Snelling, R.R. 1973b: 5. Material of the unavailable name antillana referred here: Snelling, R.R. 1973b: 5. See also: Buren, Nickerson & Thompson, 1976: 306; Shattuck, 1994: 84; Snelling, R.R. 1995: 3.

This species name has long been a cause for consternation. No type material was designated with the original description, and the description is quite vague. This is made more troublesome by our contemporary knowledge that workers in this genus show few distinguishing characteristics. The name Dorymyrmex insanus has in the past been assigned to specimens from North, Central and South America, as well as the Caribbean. Trager (1988) described some species from the southeastern United States that had previously been referred to D. insanus and Snelling (2005) clarified Caribbean Dorymyrmex were all assignable to the distinctive Dorymyrmex antillanus. This eliminated the range of D. insanus from including these areas, and is one of the few seemingly unambiguously correct revisionary changes that correctly apply to D. insanus. Subsequent treatments of this ant (Johnson 1989, Snelling 1995, Cuezzo and Guerrero 2011) differed in their conclusions about the identify and species boundaries of D. insanus. There is clearly a need for a more thorough and careful revision, including the use of molecular genetic evidence from many samples across the full breadth of the range of Dorymyrmex, to resolve problems with this name and sibling species with similar worker forms. Only then will it be clear if the Cuezzo and Guerrero (2011) description given below provides a solution to providing the best possible description of the ant D. insanus.

Worker
Cuezzo and Guerrero (2011) - (n = 55): HL: 0.78–1.16; HW: 0.70–1.00; EL: 0.22–0.57; EW: 0.15–0.22; SL: 0.80–1.12; WL: 1.08–1.44; CI: 79–96; SI: 74–119; REL: 25–71; OI: 26–82; TLI: 125–147.

Head, mesosoma, and gaster medium brown to dark; some specimens are almost black. Head and dorsal part of mesosoma covered with a dense and whitish pubescence but lighter than in D. brunneus. Head: subquadrate, convex laterally. Compound eyes placed in first cephalic third. Scape surpassing the posterior margin of head by 1/3 of its length. Posterior margin of head concave medially. Psammophore with short setae, disposed in a double file, forming a semicircle; the hairs in the top line are disposed far from the foramen magnum and do not reach the oral cavity. Mesosoma: profile interrupted in the middle, promesonotal profile higher than apical summit of propodeal tubercle. Mesonotal sclerite, in profile, forming an angle defining two faces, one dorsal and one posterior but not forming a real tubercle. In profile, the dorsal face of propodeum is feebly sinuate. Metasoma: petiolar scale directed dorsally. No ventral petiolar process.

Male
Cuezzo and Guerrero (2011) - (n = 4): HL: 0.55–0.6; HW: 0.58–0.63; EL: 0.25–0.28; EW: 0.15; SL: 0.25–0.28; WL: 1.08–1.23.

Body dark brown, mandibles yellowish brown except masticatory margin which is reddish brown. Whitish pubescence covering all the body. Head: square with round occipital corner; posterior margin of head feebly concave in the middle. Mandible falcate, with subparallel inner and outer sides, with only three teeth: apical tooth three times longer than the preapical one; there is no well differentiated angle between masticatory and basal margins; basal margin completely devoid of tooth or denticles. Posteriormargin of clypeus wide, reaching torulus; anterior margin of clypeus convex. Scape long (> or = to EL) surpassing posterior margin of compound eye; pedicel as long as each flagellomere. Compound eye large, exceeding the lateral margin of head. Hyaline ocelli well developed; lateral ocelli placed close to the posterior cephalic margin. Mesosoma: pronotum projected forwards as an elbow; parapsidal furrows strongly divergent, reaching the middle part of pronotum. Mesonotum twice longer than wide in lateral view. Anepisternum and katepisternum completely divided by a mesopleural suture. Profile of propodeum continuous, dorsal and declivitous faces not well defined. Forewing with no discoidal nor cubital cell. Hindwing with 0–3 closed cells.Hamuli with 12 hooks. Metasoma: petiole low; scale apically rounded in lateral view; ventral petiolar process short. Pygostyle short, stout and covered with white, erect setae. Stout paramere, differentiated from volsella by a sulcus; digitus curved surpassing the volsellae in length, no cuspis present; aedeagus ventrally serrate.

Type Material
Neotype. 1w, Interstate 20, 12 mi E Big Spring,Howard Co., Texas, USA, 16 April 1981, coll.byW. F. Buren, designated by Snelling 1995.

Etymology
Descriptive. Buckley's original description included a parenthetic addition "Crazy Ant" following the listing of the proper name. Both insanus (= insane) and crazy ant are fitting for characterizing these Dorymyrmex's frenetic movements and their ability to swarm upon and engulf prey, enemies and other food items.

Determination Clarifications
Despite the certainty expressed in the following passage, the validity of past and present determinations of this species are difficult to assess (see the beginning of this section and the identification section above for additional details).

Cuezzo and Guerrero (2011) - Taxonomical limits of this species are here clearly defined. In the past, the names of Dorymyrmex pyramicus and D. insanus were used as synonyms, in a sort of confusion, considering both species as one with a wide distributional range (from Texas, USA, to Argentina). Snelling (1995) was the first to recognize this mistake and to propose a clear description of D. insanus, designating a neotype worker and neoparatypes. According to him, D. insanus can be found from Central Texas to Kansas and westward to Northern California. In the same paper, Snelling says that the southern limit of its range is unclear in part due to inadequate collecting. With new material examined from Central and South America, we can confirm the presence of D. insanus in Central America and in the northern part of South America.