Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Identification
Minor worker: head length 0.94mm, head width 0.78mm, scape length 1.13mm, Webers length 1.26mm (n=1). Head without vertex collar; promesonotal and metanotal grooves well impressed; propodeal spines short; sculpture on face varying from almost entirely smooth and shining, with faint punctation medial to eyes and on the posteromedial vertex, to almost entirely foveolate; sculpture on pronotum and first gastral tergum similarly variable, from almost entirely smooth and shining to largely foveolate; color varying from light orange to dark brown.
Major worker: head length 1.77mm, head width 1.72mm, scape length 1.13mm (n=1); sides of head without erect setae.
Range
Throughout the mainland Neotropics, from Guatemala to Brazil and Bolivia. In Costa Rica: throughout the country in wet forest areas, to 1500m elevation in Monteverde.
Natural History
This species forms very large colonies. Nests may fill large rotten stumps or rotten logs (figures below). Often tell-tale piles of sawdust surround such nests, from workers excavating the interior. Workers are aggressive, and forage day or night. Large numbers of minor and major workers may be observed swarming out from nests and retrieving live insect prey, with a behavior reminiscent of army ants (figure). Kugler (1979) has termed this "gang-pulling." Workers also have an enlarged pygidial gland that segretes a noxious gummy substance used in defense (Kugler 1979). Workers tend Homoptera and visit extrafloral nectar sources. Colonies may build scattered carton shelters on low vegetation and tend membracids and other Homoptera beneath them. Workers may aggressively defend extrafloral nectar sources (e.g. Passiflora shoots), driving away herbivores and other ants. Colonies use carton construction to form baffles in rotten wood, and galleries running up tree trunks. At Rara Avis, workers were observed tending large riodinid larvae under carton galleries (figure).
Founding queens are found under loose bark of dead wood, in dead branches, and very commonly under epiphyte mats on recently fallen trees.
In Penas Blancas, Longino observed an interaction with phorid flies. Workers were streaming up a tree trunk. Phorids were hovering above. One landed on the head of a soldier. Afterwards, workers grabbed the soldier by the legs and slowly began to drag it down the trunk.
Comments
biconstricta is a complex lineage with many infraspecific taxa in the taxonomic literature. Four of these have type localities in Costa Rica:
biconstricta surda Forel 1912:222
biconstricta bicolor Emery 1890:50
biconstricta bicolor regina (unavailable quadrinomial)
biconstricta rubicunda Emery 1890:50
Wilson (2003) synonymized them all under biconstricta.
In Costa Rica, specimens from the southern Pacific lowlands are light orange. In Monteverde, they are two-toned, with light orange head and mesosoma, and somewhat darker gaster. On the Atlantic slope they are brown to dark brown. The transition can be sharp: specimens of the two-toned Monteverde form are known from open areas in and around Monteverde, on the Pacific slope west of the cloud forest that covers the continental divide; the dark brown form is common in the Penas Blancas Valley, about 5km east of Monteverde on the Atlantic slope. There is also variation in sculpture, but it does not show geographic patterns and varies within populations.
Original images of above color forms: Manuel Antonio, Monteverde, Penas Blancas, La Selva.
Literature Cited
Kugler, C. 1979. Alarm and defense: a function for the pygidial gland of the myrmicine ant, Pheidole biconstricta. Annals of the Entomological Society of America 72:532-536.
Wilson, E. O. 2003. Pheidole in the New World: A Dominant, Hyperdiverse Ant Genus. Harvard University Press, Cambridge, Mass
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
Date of this version: 4 March 2005.
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