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Camponotus Overview

Specimen List

The specimen list on which much of this website is based can be obtained by downloading this Excel file. This is the list of barcoded specimens in my database as of 21 January 2002. Exported fields include basic collection data (date, locality, collector). The list only includes barcoded specimens from Costa Rica.

Using the key and species accounts

The key is a standard dichotomous key (usually two choices per couplet but one with four). It is designed so that it can be printed out on 8.5 x 11 inch paper if desired. The numbering sequence is not continuous but instead jumps in increments of about 10. This allows new species to be added or other modifications to be made without renumbering the entire document. The key has internal hyperlinks so that clicking on a "go to" number will take you to that couplet, and clicking on the number of the couplet itself will take you back to the couplet from which it came. This makes it easy to move up and down in the key, trying different directions. Species are hyperlinked to the species accounts, so that when you arrive at a species in the key you can view the image set and information about range, morphology, and natural history. If the identification does not look right, you can return to the same spot in the key and try another avenue.

The key is based mainly on minor workers. Occasionally notes on the major workers are added when the minors of species are difficult to distinguish. If you have a collection to identify that contains both minors and majors (from a nest series) a good practice is to examine the images of the major workers in the species account and see if they match up with what you have. If you just have a major to identify, with no minors, you might be able to get some distance with the key, especially when looking at mesosomal shape characters, but beyond that you will probably have to just browse species accounts.

As is standard for this website, the species accounts have low-resolution in-line images that load with the page, but clicking on the image will load the high-resolution image. The high resolution image also contains specimen data in the form of text at the bottom of the image. The unique specimen barcode is provided, followed by an abbreviated locality. Full specimen data can be found in the Longino specimen database.

The geographic ranges of species beyond Costa Rica are abstracted from Kempf (1972) and are not very detailed.

Diacritical marks are either omitted or left in the source text as is (entered with a Macintosh). In the latter case they appear as odd characters when loaded with a browser. In particular, I often leave the latitude and longitude degree symbol in the source text, so these will load with odd characters.

This identification guide and set of species accounts for the Camponotus of Costa Rica is very much a work in progress. It should not be viewed as any kind of formal taxonomic work because I have not done much in-depth character analysis, checking of material in other collections besides my own, compilation of previous taxonomic literature, or comparison with types. The purpose of this work is mainly to capture and make available my natural history observations on what I see as Costa Rican species, and to provide a sorting tool for others attempting to identify Costa Rican Camponotus.

Another reason for the present state of this web resource is that Bill Mackay is well along in a revision of the New World Camponotus. He has already done much of the taxonomic legwork and there is no reason to duplicate his effort. In fact, this crude posting is in part motivated by Bill's revision. I wanted to summarize my natural history observations and provide identification tools for my own use, because I intend to send most of my material to Bill for identification. Thus, I expect many of my morphospecies to gradually get real names as they are identified by Bill, and some of the other species names may change as ranges and species boundaries are better understood beyond Costa Rica. Roy Snelling of the Los Angeles County Museum of Natural History also has a long-term interest in Neotropical Camponotus, and many of my identifications of material shown here are based on comparison with the LACM collection.

Species-level taxonomy

It was while sorting carpenter ants from Corcovado National Park that the magnitude of species-level tropical diversity began to dawn on me. For a while it seemed like every carpenter ant I looked at was different. Collecting in a fresh treefall would produce many specimens of perhaps five or six species, and single workers of perhaps six more, each somehow distinctive. Parts of the different species would look identical, but there would be a slight difference in petiole shape, or the amount of pubescence on the gaster, or how many hairs projected from the side of the head. I wanted to attribute these slight differences to intraspecific variation. That would have been fine if the characters had shown continuous distributions. But they didn't. The workers of a common species would all be invariant in some obscure character, and there would be this one odd specimen that was different in that character. Over time and with more collecting, patterns began to strengthen. My species concepts began to "gel" and the different forms did not seem so similar anymore. Gradually I came to accept that there are simply a lot of carpenter ant species. Local communities are diverse (32 species recorded for La Selva Biological Station) and there is high regional diversity (about 60 species for Costa Rica as a whole).

Camponotus seems to be one of those explosively radiating genera that give taxonomists headaches. If you think of a morphological hyperspace, with each spatial axis being a character series such as pilosity or propodeum shape, the genus Camponotus is a well-defined hypervolume or subspace. Individual ants map to points in that subspace. In local communities of perhaps 30 species the points form discrete clusters, and these are the discrete species in the community. However, as you add greater and greater geographic extent to your sample, the subspace gradually fills in. It seems like every possible combination of characters occurs, and characters vary continuously along the axes. You lose the ability to carve the subspace into smaller subspaces. In other words, it becomes difficult to find any well-supported monophyletic taxa within the genus.

Polymorphism

Camponotus has major workers and minor workers. Major worker development always involves allometry of head size. The mesosoma of major workers is slightly larger than minor workers, while the head is proportionately much larger. In some species the major head looks like an inflated version of the minor head, with no special modifications. In others the head shows various degrees of development of "phragmosis," which is the use of a living body part as a doorway or plug for nest entrances. All degrees of development of phragmosis occur among different species, from heads with a somewhat thickened and weakly truncate anterior portion, to a nearly cylindrical head with sharply truncate and flat anterior face. For the species with highly phragmotic heads, there seems to be a variety of convergent mechanisms for making them, involving different relative proportions of the clypeus and anterior face, and these phragmotic heads are stuck on a variety of different mesosomal forms. It appears that strong phragmosis has evolved independently in several different groups of Camponotus.

In species with weakly differentiated majors there is a high variance in minor worker size and the minors grade into the majors. Majors are just the largest of the workers, but because of the strong allometry the largest workers have very large heads and tend to be very noticeable. However, species with strongly phragmotic majors appear more strictly dimorphic rather than polymorphic, with low variance in minor and major worker size, and a big morphological gap between them.

Subgenera

Historically the genus has been divided into a number of subgenera. I am not comfortable with the subgenera because I see so much intergradation among them. Subgenus names that most Neotropical species have been assigned to are Tanaemyrmex, Myrmobrachys, Myrmocladoecus, and Myrmaphaenus. I ignore subgenera for this website.

Although this page does not contain any literature review about Camponotus taxonomy or biology, one very recent paper needs to be mentioned. Brady et al. (2000) provide a preliminary molecular phylogeny for a set of species within and around Camponotus. The monophyly of Camponotus is questioned because of the uncertain position of Polyrhachis and Dendromyrmex, and the monophyly of various subgenera is not supported. In particular, the phragmotic species placed in subgenus Colobopsis seem to occur in multiple parts of the phylogeny. Those seeking an entry to literature on Camponotus taxonomy can start with this paper.

Characters

I have not discovered any new character systems. I have used traditional characters that can be seen with a dissecting microscope.

Head shape. In full-face view the sides of the head in front of the eyes may be weakly convex and converging toward mandibles, or straight, or actually diverging so that the head is widest at the mandibles, which gives the whole head a shovel-like appearance. The head posterior to the eyes is usually evenly rounded, but may be somewhat elongate, becoming subtrapezoidal. In one species the head behind the eyes actually converges to a strongly constricted neck behind which is a flanged or flaring occipital collar.

Scape pilosity. The scape pilosity can be differentiated into pubescence and erect setae. Pubescence is a dense layer of fully appressed to subdecumbent setae that are distinctly shorter than the width of the scape. The pubescence can be so short, appressed, and sparse as to be nearly invisible. At the opposite extreme is pubescence that is relatively long and subdecumbent, giving scapes a scurfy or wooly appearance. Erect setae are strongly differentiated from pubescence. They are isolated erect to suberect hairs that are usually distinctly longer than the width of the scape. Many species lack erect setae. Others have 1-5 erect setae spread along one edge of the scape. These can be very fine and difficult to see, and the scapes need to be observed at many angles until the light catches the setae and reveals them. In only one species are there abundant erect setae. In another species the pubescence is quite long, close to the width of the scape, and fully erect. However, the hairs are very dense and very regular, suggesting strongly modified pubescence rather than erect setae. The scapes are usually terete (round in cross-section) but one species (coruscus) they are flat.

Head pilosity. In full-face view, species show great variation in the abundance of erect setae that project from the sides of the head. Almost all species have setae projecting from the posterior and posterolateral margins of the head, posterior to the compound eyes. However, there is great variation in the presence or absence of hairs between the eyes and the insertion of the mandibles. This character is often discrete, with a species having either (1) no hairs in this space, or at most 1-3 short setae clustered at the mandibular insertions, or (2) relatively abundant hairs distributed more or less evenly from mandibles to eyes.

Pronotum shape. The lateral face of the pronotum may round gradually into the dorsal face, or there may be a carina that separates the two. The carina may be complete, or it may partial. If partial, it is always present anteriorly, fading posteriorly.

Mesosoma shape. The overall lateral profile of the mesosoma, especially the combination of meso-metathorax and propodeum, varies greatly among species and I use it as a high-level separatory character to differentiate major groups. The mesosoma varies from relatively elongate (anterior-posterior axis much longer than dorsal-ventral) to shorter and more compact. The former tend to be larger species; the latter smaller. The prothorax is always separated from the rest of the mesosoma by a distinct suture. The dorsal face of the mesonotum varies in length and proportion relative to the propodeum. The mesopropodeal suture may be (1) broad and deep, breaking the dorsal profile, (2) present as a distinct suture but not breaking the dorsal profile, or (3) completely absent, the mesometathorax and propodeum forming a solid, seamless sclerite. When the mesopropodeal suture is absent, the approximate fusion point of the propodeum and mesonotum is indicated by the location of the covered metathoracic spiracle (not the propodeal spiracle). The dorsal face of the propodeum may be distinct from the posterior face, the two meeting at an angle, or the faces may be undifferentiated and form one even convexity. When separated and meeting at an angle, the angle can be very obtuse to nearly 90 degrees. When distinct, the dorsal face can be shorter then, subequal to, or longer than the posterior face. The meso-metanotal-propodeal complex grades among three states: (1) strongly tectiform or tent-like, with sides sloping to a narrow dorsal ridge, (2) somewhat box-like anteriorly, with distinct lateral and dorsal faces, converging and becoming tectiform posteriorly, so that in dorsal view the dorsal face is subtriangular, and (3) relatively box-like along the entire length, so that in dorsal view the dorsal face is subrectangular. When dorsal and lateral faces are distinct, they may round into each other, or be separated by a distinct carina. As with the pronotum, if a carina is present it begins anteriorly, fades posteriorly.

Propodeal teeth. The propodeum may have a pair of posteriorly-directed teeth at the juncture of the dorsal and posterior faces. In most cases these are species with a box-like propodeum, and the teeth are widely spaced. In one case, it is a rare species among those with a converging, subtriangular dorsal face, and the teeth are closely spaced. Among the species with fully tectiform propodeum, I have not seen any with propodeal teeth.

Mesosoma sculpture. The mesosoma can show various patterns of coarse sculpture, being entirely smooth, or entirely punctate, or some combination of smooth and punctate areas. Punctation can vary in density and depth. In some cases puncta can be irregularly oriented in lines, but I have not seen any Costa Rican species that are distinctly rugose or strongly striate or costate. The microsculpture can result in the integument surface being shiny (sublucid) or mat (dull, not shining).

Mesosoma pilosity. Dorsal pilosity varies from sparse to dense. Underlying pubescence may be absent, restricted to the dorsum, extending part way down the sides, or fully covering the mesosoma.

Petiole shape. The petiole is usually anteroposteriorly compressed and scale-like or lenticular. Less often the petiole is anteroposteriorly thickened. In lateral view the anterior and posterior faced can converge and meet at a sharp crest, or at a relatively rounded dorsum. In some cases the petiole can be subquadrate in lateral view, with a distinct, somewhat flattened dorsal face that is separate from anterior and posterior faces. The petiolar dorsum may be produced into a posteriorly directed medial tooth. Species with a petiolar tooth always have propodeal teeth, but not vice versa.

Gaster pilosity and pubescence. Like the scapes, the first gastral tergite has two kinds of hairs: erect setae and pubescence. They are usually sharply differentiated, with erect setae being relatively long and erect to suberect, and pubescence being short and appressed to subdecumbent. The gastral pubescence may be relatively sparse or dilute, exposing much of the underlying integument, or it may be very dense, nearly obscuring the underlying integument, and giving the gaster a yellow or white sheen. To see this well the specimen often has to be rotated at various angles with respect to the light. Dense pubescence can be easily seen at some angles and become nearly invisible at others.

Behavior

Camponotus are generalist foragers. They seem particularly fond of carbohydrates and are frequent visitors to extrafloral nectaries. I rarely see them being active predators. They do not recruit large numbers to resources. When recruitment is observed in Camponotus, it appears to be by tandem running. Many of the smaller species are diurnal foragers, while large species are often nocturnal. Diurnal species are often black or dark colored. Nocturnal species are often lighter red brown to yellow.

The vast majority of species in the Neotropics are arboreal. Many nest in plant cavities, usually dead stems, but sometimes in live stems. Some nest in chambers among epiphyte roots and canopy soil, and may be found by lifting and cutting into epiphyte mats. Two Costa Rican species make nests of sewn-together leaves. They use larval silk to attach leaves together and to make silk sheets and baffles. The nest walls are a combination of leaves and silk sheets. Nests in dead stems may be in (1) cavities in large-diameter soft rotten wood, (2) narrow-gauge chambers in large-diameter hard dead wood, or 3) in hollow dead stems down to 3mm outside diameter. It is not clear how much excavating Camponotus do themselves versus occupying beetle galleries and other preexisting cavities. Species clearly vary in the amount of excavating they do. Some species frequently move among nest sites and will make use of any cavity, no matter how ephemeral. These can be house pests, nesting in cardboard boxes or among clothes in a drawer. Other species nest in hollow spaces deep in the trunks or branches of live trees. These nests may be long-lived and strongly defended by major workers. Some species may nest opportunistically in ant-plants, but they may also be found in other plant cavities, live and dead. Dinah Davidson has observed a South American species that is an obligate plant-ant, but I know of none among the Costa Rican fauna. However, some species clearly seem prone to nesting in live stems, while others are found strictly in dead stems. Colonies are often polydomous, with numerous separate nests, each nest being relatively small. Colonies generally appear to be monogynous, because founding queens are most often found alone in small chambers. Camponotus striatus is the only species for which I have observed a polygynous nest.


Addendum: Fernández (2002) revised Dendromyrmex and formally synonymized it under Camponotus, making it a subgenus of Camponotus. I have updated the website to include the two Costa Rican species of Dendromyrmex (chartifex and nitidior) as species of Camponotus. This distinctive pair of species makes small nests by pulling live leaves together or folding over leaves and sewing them together with silk produced by the larvae (Wilson 1981). The walls of the nest are a combination of the leaves and a fine brown carton material made of silk and masticated plant fibers. Two other Costa Rican species of Camponotus, textor and JTL-045, make similar nests.

Species of the subgenus Dendromyrmex lack a soldier caste, unlike all other Camponotus. The workers of the small colonies are quite uniform in size. Interestingly, the two other species that make silk nests, senex textor and JTL-045, have very weak polymorphism, with soldiers only weakly differentiated from minor workers.


Literature Cited

Brady, S. G., J. Gadau, and P. S. Ward. 2000. Systematics of the ant genus Camponotus (Hymenoptera: Formicidae): a preliminary analysis using data from the mitochondrial gene cytochrome oxidase I. Pages 131-139 in A. D. Austin and M. Dowton, editors. Hymenoptera. Evolution, biodiversity and biological control. CSIRO Publishing, Collingwood, Victoria.

Fernández C., F. 2002. Revisión de las hormigas Camponotus subgénero Dendromyrmex (Hymenoptera: Formicidae). Papéis Avulsos de Zoologia, Sao Paulo 42:47-101.

Kempf, W. W. 1972. Catalogo abreviado das formigas da Regiao Neotropical. Studia Entomol. 15:3-344.

Wilson, E. O. 1981. Communal silk-spinning by larvae of Dendromyrmex tree-ants (Hymenoptera: Formicidae). Insectes Sociaux 28:182-190.


Page author: John T. Longino longinoj@evergreen.edu


Date of this version: 24 August 2004.
Previous versions of this page: 22 January 2002
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