Myrmicinae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Mexico, Belize, Costa Rica. Costa Rica: San Luis Valley near Monteverde.
Identification
The extremely long petiolar peduncle and short compressed node is unique among Costa Rican Pheidole, and is a very rare condition in Pheidole in general. This, together with the large propodeal spines and strong rugose sculpture, give this ant a very distinctive habitus. It is unmistakable, although it may be difficult at first glance to tell it is a Pheidole! The petiole looks exactly like those of the long-petiolate Temnothorax formerly in Macromischa.
Natural History
The types were collected in Mexico. In Wilson's (2003) revision he reports a minor worker from Teoviscocla, near Cuichapa, Veracruz, Mexico. It was collected in 1960 by a Cornell University Field Party, at a 1600m elevation site, tropical forest with plantings of coffee. Gordon Snelling just reported another collection from Belize. He reported it on his Name that Ant website.
I know this species from only one locality in Costa Rica. In 1989 I was visiting the San Luis waterfall. The San Luis valley is on the Pacific slope below Monteverde, and near the upper part of the valley, at about 1100m, is a tall waterfall. From the base of this waterfall a major stream flows down a wooded ravine and out into the upper farms of the valley. I found several workers foraging on stones at the very edge of the stream, near the base of the waterfall. I returned in 1994 and found a few additional workers in the same circumstances.
Comments
This is a spectacular ant. When I first encountered it I didn't know where to put it. The petiole made me think of Macromischa. They sat around in my Leptothorax (now Temnothorax) drawer for over a decade, gathering dust (figuratively). In preparing the Leptothorax of Costa Rica web pages, I took a close look at them again. On close inspection of the mandibles it immediately became clear that they had the characteristic Pheidole dentition (Figure: small, large), as outlined in Bolton's key to genera. I then leafed through Wilson's revision looking at the illustrations until I found a match at ursus. On the off chance P. ursus would have some information on the web, I did a search and encountered Gordon's Name that Ant!
I still think this is a very strange Pheidole, and I hypothesize it is a very primitive one. The propodeal spines and the petiole structure look exactly like those of Pheidole primigenia Baroni Urbani, an extinct species from Miocene amber of the Dominican Republic (Baroni Urbani 1995, also see figure in Wilson 2003:12). It could be that long petioles were popular in the Miocene, but as ants increasingly dominated the terrestrial realm they became a liability (easily snipped by other ants). Long-petiolate Temnothorax could date from the same era, with a relict stronghold in Cuba and a very sparse occurrence on the MesoAmerican mainland today. Thus P. ursus could be an ancient and relict Pheidole, with a spotty distribution in mid-elevation habitats of MesoAmerica.
Literature Cited
Baroni Urbani, C. 1995. Invasion and extinction in the West Indian ant fauna revisited: the example of Pheidole (Amber Collection Stuttgart: Hymenoptera, Formicidae. VIII: Myrmicinae, partim). Stuttg. Beitr. Naturkd. Ser. B (Geol. Palaontol.) 222:1-29.
Wilson, E. O. 2003. Pheidole in the New World: A Dominant, Hyperdiverse Ant Genus. Harvard University Press, Cambridge, Mass.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. longinoj@evergreen.edu
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