Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Identification
Minor worker: head length 0.72mm, head width 0.67mm, scape length 0.71mm, Webers length 0.94mm (n=1). Scapes feebly foveolate; head broadly rounded behind; promesonotum evenly arched, mesonotal suture absent; propodeal spines short, upturned; face, pronotum, and gaster smooth and shining; katepisternum and propodeum coarsely rugose and shining or completely smooth and shining; dorsal pilosity abundant, long, flexuous, those on posterior half of promesonotum curved anteriorly; color red brown.
Major worker: head length 2.19mm, head width 1.79mm, scape length 0.77mm (n=1). Face densely reticulate rugose; conspicuous antennal scrobes extending to just above eye, surface of scrobe smooth and shiny; hypostomal margin with low, broadly rounded medial lobe, pair of robust subtriangular teeth located closer to midline than to recessed teeth flanking mandibles; dorsal pilosity abundant; head with abundant setae projecting from sides of head in face view.
Range
Costa Rica: Atlantic lowlands (La Selva Biological Station and adjacent Barva transect to 500m elevation).
Natural History
This species inhabits lowland rainforest and so far is only known from a small area in Costa Rica. Workers are moderately abundant in Winkler samples, Berlese samples, and at baits on forest floor. Workers occasionally occur in Malaise samples.
Nests are in clay soil. Stefan Cover and E. O. Wilson independently observed nests in clay soil at La Selva. Longino observed a nest in a clay bank at the Cantarrana site on the Barva transect (300m elevation). A column of workers was climbing up the bank and entering a hole. Several centimeters deep was a chamber about 3cm wide and 5mm tall, filled with workers and brood. A small tunnel led down from this chamber to a very similar lower one, 1-2cm below the first. When the top chamber was opened, workers flowed down into the lower chamber. When the lower chamber was opened, workers continued to flow down another tunnel, presumably to a yet lower chamber that was not excavated. There was abundant brood, many large soldiers, and the occasional adult male.
Comments
We used to recognize a distinct morphospecies, JTL-081, that differed from vestita in the sculpture of the katepisternum and propodeum. In vestita the katepisternum and propodeum (dorsal and lateral surfaces) were overlain with coarse rugae. In JTL-081 these surfaces were mostly smooth and shining (see images below). The differences seemed discrete, with no intermediates. Measurements of minor worker head length and scape length revealed the pattern in the graph below, in which the vestita were all larger than JTL-081. We now treat these as a single species, but the pattern remains unexplained. Perhaps the workers lacking rugae are nanitics. However, in collections (Winkler, baiting) this form is as or more abundant than the rugose form.
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Above: minor worker of morphospecies JTL-081, now considered a form of vestita.
Above: graph of HL vs. SL for P. vestita minor workers. Red points are rugose form; black points are smooth form.
Page authors:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. longinoj@evergreen.edu
Stefan Cover, Museum of Comparative Zoology, Harvard University, Cambridge MA 02138 USA. scover@oeb.harvard.edu
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