Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Southern Mexico to northern Argentina. Costa Rica: widespread in lowland habitats, wet and dry forest, to 1100m on Volcan Cacao.
Identification
Black satiny surface; no erect setae on mesosomal dorsum; bright yellow antenna tips. Nearly identical in morphology and behavior to P. verenae, with which it is nearly always sympatric. Pachycondyla verenae has brown antenna tips, and the petiole is slightly more margined posteriorly.
Natural History
In both wet and dry forested lowlands of Costa Rica, this is one of the most common and conspicuous ants. Foraging workers are extremely fast and run over the surface of trails in a nervous, erratic manner, with the antennae rapidly vibrating. Their behavior is reminiscent of pompilid wasps. Foragers are solitary hunters on the ground, where they capture live prey and scavenge on dead insects. They are never arboreal. I have only seen diurnal foragers; I do not think they forage at night. The nests are in dead wood on the ground.
Colonies are apparently monogynous, with a single queen responsible for most reproduction, but there is also a dominance hierarchy among workers (Oliveira and Hoelldobler 1990). Dominant workers are aggressive toward subordinates, have more developed ovaries, lay more eggs, and attend the egg pile more. Dominant workers thus have the potential to reproduce, because they lay haploid eggs even in the presence of the queen, and these eggs may develop into males (Oliveira and Hoelldobler 1990).
Fresneau (1985) investigated foraging in field colonies of apicalis. Workers foraged individually, and no recruitment was ever observed. Foragers had a high degree of regional specialization over time, and seemed to use visual ques for orientation. Tandem running was observed during a nest emigration, but never during foraging. Goss et al. (1989) studied foraging behavior of three colonies and developed a general model of foraging in social insects. Fresneau and Dupuy (1988) studied division of labor, and found that workers exhibit a temporal polyethism common among ants, in which workers begin in brood care, graduate to nest maintenance activities, and lastly become foragers. Fresneau and Dupuy also observed new alate queens participating in tasks similar to workers, a trait they considered primitive relative to other ants.
Soroker et al. (1998) examined colony odor formation, using radioactive tracers to tag lipid precursors. Lipids in the cuticle and the postpharyngeal gland were transferred among workers largely by allogrooming, and not by trophallaxis. Pavan et al. (1997) and Giovannotti (1996) have studied sound production in apicalis and the ultrastructure of the stridulatory apparatus. Schmidt et al. (1980) investigated venom toxicity, and Cruz and Morgan (1997) have examined venom chemistry.
During field work in Corcovado National Park in 1980, I had the opportunity to watch a colony over a period of several months. The nest was inside a 1m diameter fallen tree trunk, which was suspended 1m off the ground by its branches. The nest entrance was on the underside. I found this nest by following a returning forager. While doing a mark-recapture study on Heliconius butterflies, I spent several hours at a time at this site. While waiting for butterflies, I would often capture tabanids, lightly crush them, and feed them to ants. One day I decided to follow an apicalis worker that picked one up. It took a torturous route, up and down, backwards and forwards, taking many dead end routes from which it would return and take another. After some time, it reached the nest entrance, 10-12m from where it started. Within a minute of the time it entered the nest, a second worker arrived at the entrance with another one of my crushed tabanids. These observations are consistent with Fresneau's view that apicalis uses visual cues, such as canopy pattern, for orientation.
Another observation at the same site revealed an interesting feature of apicalis foraging behavior. One morning I set out a handkerchief on which I accumulated a dozen or so crushed tabanids. An apicalis worker found them first, and spent a long time just going from fly to fly biting off the wings. After a while Solenopsis geminata and Crematogaster erecta began to arrive. Two apicalis workers were on the handkerchief by this time, and they began to carry flies off. An apicalis worker dashed in and grabbed one last fly from the Solenopsis, but from then on it was Solenopsis and Crematogaster territory. The lengthy processing of multiple prey items was definitely not beneficial in this context. Maybe the apicalis worker bit off the wings of a dozen flies before doing anything else because that is step one in the program upon seeing dead insects, and seeing more than one dead insect in any one place is not a common event.
At La Selva, I have observed three nests. One was a colony foundress with a single worker in a chamber in a rotten log on the ground.
The next nest was in a soft rotten stem in the leaf litter. The stem was horizontal, half buried in litter, and half projecting over the trail. The stem was evenly cylindrical, approximately 5cm outer diameter, 3cm inner diameter. The outer, projecting portion of the stem contained soil and nest refuse. A Strumigenys colony was present in this refuse. Continuing basally was the main refuse pile. This was swarming with small white collembola, and numerous shelled gastropods. Basal to the refuse pile was the brood pile, with numerous cocooned pupae, and larvae of all sizes. There were about 100 adult workers, and about 20 adult males. I saw no queen. Approximately a quarter to a third of workers had mites clinging to the pygidium, clustered around the sting. These were visible in the field as small orange tufts at the tip of the abdomen. Later examination in lab revealed that the mites, up to 6 at a time, clung to individual setae on the pygidium. Also, I occasionally found a single mite on the inferior metatibial spine. I found a few mites clinging to tubercles on the larvae. The refuse was composed of abundant chitinous fragments (elytra, pronota, etc.) embedded in brown organic matter. Prionopelta workers were observed in cavities in the walls of the dead stick, beneath the refuse pile. I preserved most of the colony, but left a plastic bag in the lab with four workers and several pieces of the nest, including part of the refuse pile. Several days later I reexamined the contents. The refuse pile was swarming with collembola and immatures of the phoretic mites. The four workers that had remained in the bag were encrusted with adult mites, the mites clinging to setae on the tibiae and tarsi, up to 30 per leg. There was one larger mite, not the same as the phoretic mites, which I found in the refuse pile and preserved in alcohol.
A third nest was just three workers in a small chamber in a small dead trunk. The workers had the same type of mites as before, clinging to the tip of the abdomen.
Type Data
Formica apicalis Latreille 1802:204. Syntype worker: South America.
Comments
Wild (2005) recently revised the apicalis complex. The abstract follows.
The taxonomy of the Neotropical Pachycondyla apicalis species complex is revised. Contrary to the widely-held view that the apicalis complex contains only two species, P. apicalis (Latreille 1802) and P. obscuricornis (Emery 1890), morphological evidence indicates the existence of three broadly sympatric species. Examination of type specimens reveals that the name obscuricornis has been extensively misapplied in the literature, and that the valid name for the widespread species commonly misdiagnosed as P. obscuricornis is P. verenae (Forel 1922). True P. obscuricornis is shown to be an uncommonly collected South American species. The name apicalis is valid as currently employed for that species. A taxonomic key is provided, along with diagnoses, illustrations, and distributional data for all three species.
Literature Cited
Cruz L., L., and E. D. Morgan 1997. Explanation of bitter taste of venom of ponerine ant, Pachycondyla apicalis. Journal of Chemical Ecology 23:705-712.
Fresneau, D. 1985. Individual foraging and path fidelity in a ponerine ant. Insectes Sociaux 32:109-116.
Fresneau, D., and P. Dupuy 1988. A study of polyethism in a ponerine ant Neoponera apicalis (Hymenoptera, Formicidae). Animal Behaviour 36:1389-1399.
Giovannotti, M. 1996. The stridulatory organ of five Ponerinae species: A SEM study (Hymenoptera, Formicidae). Fragmenta Entomologica 28:157-165.
Goss, S., Fresneau, D., Deneubourg, J. L., Lachaud, J. P., and J. Valenzuela Gonzalez 1989. Individual foraging in the ant Pachycondyla apicalis. Oecologia 80:65-69.
Latreille, P. A. 1802. Histoire Naturelle de Fourmis, et recueil de memoires et d'observations sur les abeilles, les araignees, les faucheurs, et autres insectes. 445 pp. Paris.
Oliveira, P. S., and B. Hoelldobler. 1990. Dominance orders in the ponerine ant Pachycondyla apicalis (Hymenoptera, Formicidae). Behav. Ecol. Sociobiol. 27:385-393.
Pavan, G., M. Priano, P. De Carli, A. Fanfani, M. Giovannotti 1997. Stridulatory organ and ultrasonic emission in certain species of ponerine ants (Genus: Ectatomma and Pachycondyla , Hymenoptera, Formicidae). Bioacoustics 8:209-221.
Schmidt, J. O., M. S. Blum, and W. L. Overal 1980. Comparative lethality of venoms from stinging Hymenoptera. Toxicon 18:469-474.
Soroker, V., D. Fresneau, and A. Hefetz 1998. Formation of colony odor in ponerine ant Pachycondyla apicalis. Journal of Chemical Ecology 24:1077-1090.
Wild, A. L. 2005. Taxonomic revision of the Pachycondyla apicalis species complex (Hymenoptera: Formicidae). Zootaxa 834:1-25.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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