Stenamma schmittii

Every Ant Tells a Story - And Scientists Explain Their Stories Here
Jump to navigation Jump to search
Stenamma schmittii
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Stenammini
Genus: Stenamma
Species: S. schmittii
Binomial name
Stenamma schmittii
Wheeler, W.M., 1903

Stenamma schmitti casent0104796 profile 1.jpg

Stenamma schmitti casent0104796 dorsal 1.jpg

Specimen labels

A forest species that forms colonies containing hundreds of workers.


Smith (1957) - The worker can be distinguished by the size and structure of the eye; the nature and appearance of the sculpturing of the body; the usually well developed and very distinct mesoepinotal impression; shape and proportions of the petiolar and postpetiolar nodes. The worker is most apt to be confused with that of Stenamma impar. It differs especially in the smaller eye, the larger and more coarsely sculptured and also more opaque body.

Stenamma schmitti is a highly variable species in many respects. Such variations especially apply to the size of the eye and the number of ommatidia in its greatest diameter; the number (usually 4-6) and size of the basal teeth of the mandibles; the size and shape of the mesoepinotal impression, size of the epinotal spines, shape and proportions of the petiolar and postpetiolar nodes. The color and sculpture of the body are very variabLe as is also the degree of development of the longitudinal rugulae and shagreening on the first segment of the gaster.


Quebec, Maine to North Carolina and west to Minnesota and Missouri

Distribution based on Regional Taxon Lists

Nearctic Region: United States (type locality).

Distribution based on AntMaps


Distribution based on AntWeb specimens

Check data from AntWeb


Smith (1957) reports: It appears Stenamma schmittii is primarily a woodland loving form which is capable of living in fairly dry to moist habitats. Colonies are usually found nesting in the soil beneath stones, logs, rotten wood, moss, leaf mould, and other debris and are often difficult to find. The species has been collected at altitudes ranging from only a few hundred feet to approximately 5,000 feet. Mary Talbot has excavated a number of colonies in the Droste Woodsin St. Charles County, Missouri. She has found colonies apparently containing from only one to four chambers and at depths of 5 to 15 inches. It appears that there is only a single mother queen per colony. The largest colony examined, on September 29, 1950, consisted of four chambers at depths of 5, 6, 7, and 10 inches. The colony contained 310 workers, 31 alate females and 35 males, 9 eggs, and 67 larvae. No pupae were seen, nor was the mother queen found. Miss Talbot did not think that this was a hibernating colony. Her general observations on Stenamma schmittii indicate that alate females and males are produced in late summer, by some colonies at least, and that these castes overwinter in the parental nest until the following spring. The most common if not the only immature stage in which the ant overwinters is the larval.

Talbot (1957) added additional information from a study where she excavated soil during the cooler months of the year, in a Missouri woodland, on order to survey ant nests. Stenamma schmitti was slightly less common, being collected seven times. Males and females were found in September and October. Evidently flight is late in this species. Chambers were well defined and slightly larger than those of the previous species. Four colonies had one chamber, while the remaining three occupied two, three, and four chambers respectively. The depth of chambers ranged from five to fifteen inches, and the mean was 10.5 inches. Complete colonies were collected only four times; these gave a mean population of 227, of which 121 were workers.

Smtih (1957) also provides a communication from Brown regarding schmitti: ""The workers appear to have no set way of approaching the collembolans, but merely rush their prospective prey with mandibles opened wide. The collembolans usually manage to escape if attacked in an open space between the leaves in my jar, but if caught in a crevice or pocket, they have little chance of getting away. The attack by the ants is clumsy and hurried, in contrast to the finesse displayed by the collembola catching dacetines, and there Seems little doubt that springtails form only' a part of their diet. Use of the sting has not yet been observed but the rapid immobilization of the colIembolan renders stinging a possibility to be considered when conditions of observations can be made more favorable than they were in the cases studied."


The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • schmittii. Stenamma brevicorne subsp. schmittii Wheeler, W.M. 1903d: 167 (diagnosis in key) (w.) U.S.A. Smith, M.R. 1957b: 144 (q.m.). Raised to species: Creighton, 1950a: 138.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.



Smith (1957) - Length 2.5-3.5 mm. Second through the sixth funicular segments broader than long, the last segment of the antennal club approximately as long as the combined lengths of the three preceding segments. Eye extremely small to very small, the greatest diameter 0.10 mm and composed of three to six ommatidia. Thorax, in profile, usually with a very pronounced mesoepinotal impression which is often 0.10 mm in length and proportionally as deep. Epinotum commonly sloping posteriorly, the base and declivity meeting to form a pair of distinct but variably sized spines, which range from about one-sixth to one-fourth the length of the base of the epinotum. Petiolar node, in profile, rounded to subangular resembling that of impar but perhaps not quite so extreme; from above and behind, although it resembles that of impar, it is usually blunter and more rounded. Postpetiolar node, from above, subcampanulate to subrectangular, with the bluntly rounded apex of the node directed somewhat posterodorsad. Longitudinal rugulae at the base of the gaster varying from obsolescent to moderately well developed, ranging in length from less than 0.10 mm to slightly more.

Frontal area smooth and shining. Front with posteriorly diverging, longitudinal striae, remainder of head largely reticulate or rugulose.reticulate, with punctate interspaces. Sides of thorax longitudinally rugulose and also densely punctate, the punctures sometimes predominating over the rugulae, especially in certain parts; mesopleuron often largely punctate. Thorax above, varying from fine to very coarsely regulose.reticulate or rugulose with punctate interspaces; often the rugulae on the promesonotum have a longitudinal trend. Petiolar and post petiolar nodes largely densely punctate but not always opaque. The shagreening on the first gastric segment varies from obsolescent to moderately well developed, the sculpturing more evident in some lights than others. Head and thorax subopaque or opaque, the petiolar and postpetiolar nodes less so, the gaster smooth and shining.

Body highly variable in color ranging from a yellowish brown or light brown through reddish brown to almost blackish; appendages lighter, gaster usually light at the base and apex with an infuscated, transverse band midway of its length.

This is a highly variable species in many respects. Such variations especially apply to the size of the eye and the number of ommatidia in its greatest diameter; the number (usually 4-6) and size of the basal teeth of the mandibles; the size and shape of the mesoepinotal impression, size of the epinotal spines, shape and proportions of the petiolar and postpetiolar nodes. The color and sculpture of the body are very variable as is also the degree of development of the longitudinal rugulae and shagreening on the first segment of the gaster.


Smith (1957) - Similar to the worker except as described below.

Length 4-4.3 mm. Anterior ocellus located 0.35-0.40 mm back of frontal area. Antennal scape failing, by its greatest breadth or less, to attain the posterior border of the head. Greatest diameter of eye approximately 0.2 mm and with 12-14 ommatidia. Viewed frontally, the anterior border of the eye is located about 0.25-0.30 mm posterior to the base of the mandible. Thorax from the anterior border of the pronotal collar to the apices of the epinotal spines 1.45-1.55 mm in length, widest slightly anterior to the wing insertions where it measures 0.70-0.75 mm; humeri subangular. Venation of anterior wing similar to that of occidentale. Veins and stigma light brown or yellowish. Thorax with tuberculate to normal shaped spines which are 0.10 mm or less in length. Petiole, in profile, pedunculate with subangular to distinctly angular node. Postpetiole, in profile, 0.3 mm high, convex above, almost as high as long. Petiolar node, from behind, with dorsally converging sides and weakly rounded to subtruncate superior border. Postpetiole from 0.25-0.30 mm broad, approximately as broad as long.

Thorax above, coarsely rugulose-reticulate; the longitudinal rugulae somewhat convergent toward the middle of the anterior border of the mesonotum. Scutellum often more finely, sculptured than the mesonotum. Area above the epinotal spines transversely rugulose-punctulate. Side of the anterior coxa transversely rugulose-punctate. Petiolar and postpetiolar nodes above rugulose- or rugulose-reticulate, punctulate, subopaque. Much of the first gastric segment varying from finely reticulate and subopaque to smooth and shining (the reticulations more distinct in, some lights than others); Frontal area and infraspinal area smooth and shining.

Pilosity yellowish to golden, fairly abundant, slender, consisting of variable lengthened hairs that are suberect to erect. Pubescence on legs and scapes rather dense.

Occasionally there may be infuscated spots on the head and thorax, or the head and thorax may be darker than the rest of the body. The gaster may vary from brown to blackish but the apex is apparently righter than the remainder; commonly the darker portion gives the appearance of a broad, transverse band.

There is considerable variation in color as well as in some of the body proportions., As mentioned above much of the first gastric segment may be finely reticulate or else smooth and shining.


Smith (1957) - Length 3.3-3.5 mm. Head approximately twice as long posterior to the eyes as in front of the eyes. Eye large, convex, protuberant, 0.20-0.25 mm in length and more than 0.10 mm in width. Anterior ocellus located approximately 0.2 mm posterior to the frontal area. Clypeus convex above and bearing a longitudinal furrow or impression, the anterior border of the clypeus arched. Mandible subtriangular, with 3-4 distinct teeth. Scape exceptionally short, usually 0.23-0.25 mm long and approximately as long as the combined lengths of the first three funicular segments. Thorax from the anterior border of, the pronotal collar to the articulation with the peduncle of the petiole, 1.2-1.5 mm in length; widest anterior to the articulations of the anterior wings where it measures, 0.65-0.75 mm. Mesonotum with distinct Mayrian furrows, the parapsidal sutures indistinct to distinct but more commonly distinct. Epinotum, in profile, with concave basal surface, which is approximately 0.35-0.40 mm in length and meets the declivity in either an angle or an angular tubercle. Petiole, in profile, with the peduncle meeting the node above to form a bluntly rounded to distinct angle_ Petiole and postpetiole, from above, slender in appearance but the postpetiolar node' often almost as broad as long.

Frontal region of head to at least as far: posteriorly as the anterior ocellus very finely longitudinally striated, remainder of the ,head, for' the most part, densely and finely punctulate. Thorax largely punctulate; in some' lights there are discernible above, on at least the posterior part of the mesonotum, very fine, longitudinal striae. Side of epinotum longitudinally to irregularly rugulose-punctulate. Petiolar and postpetiolar nodes above, largely smooth and shining; on the sides the punctures are more apparent but never dense. Dorsal surface of epinotum, petiolar and, postpetiolar nodes, and gaster shining; remainder of body subopaque. Mesopleuron and anterior portion of mesonotum often shining, at least in some lights; the mesopleuron frequently smooth or very finely sculptured.

Pilosity consisting largely of short, suberect hairs; those on the anterior border of the clypeus unusually long.

Body blackish to black, with yellowish mandibles, antennae and tarsi; apex of the coxae and gaster, trochanters, and the, articulations of the femora and tibiae lighter than the remainder of the segments.

Males vary considerably in size, proportions of the body, and sculpture. The scutellum is sometimes almost, smooth and shining. The first segment of the gaster may bear fine reticulations or punctulations.

Type Material

St. Vincent, Pennsylvania, 1-1/2 miles SW of Latrobe in Westmoreland County. P.J. Schmitt. American Museum of Natural History, Museum of Comparative Zoology at Harvard College


Patronym. Described from workers collected by P. J. Schmitt.


  • Smith, M. R. 1957. Revision of the genus Stenamma Westwood in America north of Mexico (Hymenoptera, Formicidae). American Midland Naturalist. 57:133-174.
  • Talbot, M. 1957. Populations of ants in a Missouri woodland. Insectes Sociaux. 4:375-384. DOI:10.1007/BF02224157
  • Wheeler, W. M. 1903a. The North American ants of the genus Stenamma sensu stricto. Psyche. 10:164-168. DOI:10.1155/1903/45280.