Pheidole anastasii

A common and abundant forest species.

Identification
One of a number of species once suggested (Wilson 2003) to be the single highly variable species P. bilimeki. P. anastasii overlaps in its range with the now more strictly defined P. bilimeki. These two species maintain clear ecology differences, primarily in habitat preferences, that are diagnostic: P. anastasii nests in plant cavities in the shaded understory of mature or second growth wet forest. In contrast, bilimeki nests almost anywhere, including in rotten wood and under stones, but occurs mostly in open and highly disturbed areas.

Distribution
Panama to Guatemala and southern Mexico (Chiapas).

Distribution based on Regional Taxon Lists
Neotropical Region: Belize, Costa Rica, Guatemala, Honduras, Mexico, Nicaragua, Panama. Palaearctic Region: Denmark, Germany.

Biology
Longino and Cox (2009) - Pheidole anastasii is a very abundant species in the low arboreal stratum of primary wet forest understory throughout Costa Rica. Nests may be found in almost any kind of cavity or sheltered space, and they may augment their nest space by building galleries and tunnels with carton or earthen construction. Nests have been observed in cavities in live stems of Psychotria (Rubiaceae), Witheringia asterotricha (Solanaceae), and Pausandra trianae (Euphorbiaceae), bracts of Ischnosiphon (Marantaceae), clasping petiole bases of Araceae, and the bulbous leaf bases of Tillandsia bulbosa (Bromeliaceae). It is a common opportunistic inhabitant of myrmecophytes such as saplings of Cecropia, portions of myrmecophytic Ocotea trees abandoned by Myrmelachista, and myrmecophytic Piper species. In every Costa Rican population of myrmecophytic melastomes (those with petiolar or laminar pouches; Conostegia setosa, Clidemia sp., Tococa sp.) that has been observed (Corcovado, La Selva, Tortuguero), this species has been the most abundant inhabitant. It was the dominant ant in a study of Conostegia setosa at La Selva (Tennant 1994). The species also nests in dead sticks and branches on or above the forest floor, and under bark flaps on tree trunks. When nests are in myrmecophytic melastomes, carton galleries may occur on the outside, connecting pouches and extending down the stem to the ground.

Colonies appear to be polydomous. Workers are generalist foragers, and may be taken at baits or in samples of sifted leaf litter. Colonies have occasionally been found as exotics in greenhouses in the United States (New York, Washington D.C.), which is no surprise given the frequency with which it is found in live plant cavities in Central America.

Specimens from the Caribbean coast of Panama, at the southernmost limit of the species, are the most aberrant. Minors and majors are identical to Costa Rican P. anastasii with respect to shape and measurements, but differ in color. Instead of being clear yellow orange, minors are a dusky gray brown and majors similar but with the posterior third or more of the head yellow (approaching Pheidole punctatissima). The specimens were collected in ant-plant domatia in forest understory, thus matching the behavior of P. anastasii.

At La Selva Biological Station, in lowland rainforest on the Atlantic slope, P. anastasii is one of the most abundant ants in the forest understory. At Sirena in Corcovado National Park in southeastern Costa Rica, P. anastasii is a common understory ant in mature and second growth forest, much like it is at La Selva.

Pheidole anastasii has a relatively consistent morphology and behavior over most of its range. Most collections are from Costa Rica (over 350 separate collection events in JTL's specimen database) but a few collections have been examined from Panama, Nicaragua, Honduras, Guatemala, and Mexico (Chiapas). All collections are from wet forest habitats, most from below 500m elevation but with a few to a maximum of 1200m. The northernmost record is from rainforest near Tikal in the Peten of Guatemala, and these specimens are indistinguishable from Costa Rican material.

Nomenclature

 *  anastasii. Pheidole anastasii Emery, 1896g: 76 (s.w.) COSTA RICA. Forel, 1901h: 78 (q.). Junior synonym of bilimeki: Wilson, 2003: 378. Revived from synonymy: Longino & Cox, 2009: 40.

Description
Longino and Cox (2009) - Pheidole anastasii, Pheidole bilimeki, Pheidole jamaicensis and Pheidole punctatissima share the following traits:

Minor worker: head width (not including eyes) 0.38 to 0.55mm; scape length 0.40 to 0.60mm; scape index (100 * scape length / head width) 95 to 125; face and mesosoma uniformly foveolate; promesonotal groove very weakly or not at all impressed; with short upturned propodeal spines; postpetiole broad and low, somewhat flattened, lower than petiolar node; first gastral tergite with anterior third to entire surface shagreened; pilosity on mesosomal dorsum sparse and stiff; pilosity on hind tibia fully appressed and short.

Major worker: head width 0.74 to 1.09mm; scape length 0.44 to 0.63mm; scape index 50 to 68; face largely foveolate rugose, with variable extent smooth and shiny posteriorly; hypostomal margin with two closely-spaced medial teeth; first gastral tergite with anterior third to entire surface shagreened.

In comparison with P. bilimiki, minor workers of Pheidole anastasii have relatively longer scapes and the posterior margin of the head is more rounded, both majors and minors are uniformly yellow orange.