Stenamma diecki

This widespread species lives in a wide variety of habitats and is extremely variable in form.

Identification
Snelling (1973) carefully explained how to identify these ants:

Over much of the western range it is sympatric with the equally tolerant and variable Stenamma occidentale (=Stenamma snellingi).

Stenamma species can be difficult to tell apart. The following is modified from Snelling 1973. It discusses differences between Stenamma diecki and Stenamma occidentale and also highlights some of the problems in identifying Stenamma collections to species.

Stenamma diecki: the median lobe of the clypeus possesses a fine transverse carinula below the summit of the declivity between the two lateral carinulae; the median lobe, in profile has definite dorsal and anterior surfaces, the latter clearly "undercut" below; the sides of the pronotum are sharply longitudinally rugulose, with distinctly shiny interspaces; the mesopleura, although with numerous fine punctulae, is moderately shiny and with several distinct oblique rugulae; the upper half of the side of the propodeum bears several longitudinal rugulae; and the anterior face of the metanotal groove, in profile, is vertical or nearly so, the groove flat along the length.

Stenamma occidentale: the median clypeal lobe lacks a clearly defined transverse carinula and in profile the lobe is evenly, strongly convex, without defined dorsal and anterior surfaces, the latter not sharply "undercut"; the sides of the pronotum are densely punctate, longitudinal rugulae largely effaced; the mesopleura barely shiny, densely punctate and without evident rugulae; the upper half of the propodeal sides closely punctate, dull and without defined longitudinal rugulae; the metanotal groove, in profile, either broadly V-shaped, or if long, the anterior slope oblique rather than vertical.

These differences between the two types, while perfectly obvious in many specimens, are subject to much variation and many specimens are thus difficult to correctly place. The variation of greatest significance is perhaps that of thoracic punctation. The sides of the pronotum are longitudinally rugulose in both species, the rugulae very fine and irregular in Stenamma occidentale, coarse and sharp and widely spaced in Stenamma diecki. The interspaces are, in Stenamma diecki, usually concave, smooth, shiny and without evident punctulae. Specimens do show up, however, which do have punctulae in these interspaces; the punctulae are fine, often visible only in oblique lighting, and most often separated by more than a puncture diameter. Those specimens which do have punctulate propleurae have the punctulae confined to the lower half or less and the punctulae do not obscure the decidedly shiny overall aspect of the segment. In those insects which I interpret to be Stenamma occidentale the entire propleura is closely punctulate and the punctures evenly distributed and the overall appearance is of a dull, or barely shiny, segment.

The mesopleura of Stenamma diecki is variable, but is usually more or less closely punctulate, varying from moderately to strongly shiny, dependent upon the density and depth of the punctulae. Although occasionally reduced or absent, rugulae are usually present and distinct. These rugulae may be strictly longitudinal or may extend obliquely from the upper anterior angle toward the lower posterior corner. In Stenamma occidentale the mesopleura is barely shiny, closely and deeply punctulate. Usually absent, occasionally one or two fine, indefinite longitudinal rugulae may be present.

The propodeal sides of Stenamma diecki always bear coarse longitudinal rugulae over the entire surface; these are sometimes reduced over the posterior portion of the upper half. The interspaces are punctulate, the punctulae most often fine and sparse, the surface moderately shiny. In this species, too, the basal face of the propodeum is definitely shiny, with fine, obscure, sparse punctulae. Sometimes fine transverse rugulae may be present and in a few specimens the basal face is reticulate-rugulose. Dense punctation on both lateral and basal faces is characteristic of Stenamma occidentale, the lateral face rarely with a few fine, obscure longitudinal rugulae on the sides at or below the level of the spiracular opening.

The profile of the metanotal groove is variable in both species, but in Stenamma diecki it is usually long. The posterior slope of the mesonotum, which sets off the groove anteriorly is usually vertical, or nearly so, as is the anterior slope of the basal face of the propodeum. In this species, the "floor" of the metanotal groove is, in profile as long as the groove is deep or longer. In Stenamma occidentale the groove is most commonly broadly V-shaped in profile, without a definite "floor." Some specimens have been seen in which this is not true; in these, however, the posterior slope of the mesonotum is strongly oblique, rather than vertical, and the anterior slope of the basal face of the propodeum is similarly inclined. In a few specimens the basal face of the propodeum almost entirely lacks the anterior slope and the mesonotal groove is thus very poorly delimited and is quite shallow.

Other differences exist between the workers of these species, but are too variable to be used reliably. Eyes tend to be larger in Stenamma diecki, the OMD correspondingly less; cephalic rugulae are usually coarser in Stenamma diecki; the pronotal humeri are usually more pronounced in Stenamma diecki and in this species the nodes of the petiole and postpetiole are usually shiny and occasionally lightly rugulose. These conditions are usually contrasted in Stenamma occidentale which is also, on the average, a smaller species.

Distribution based on Regional Taxon Lists
Nearctic Region: Canada, United States. Neotropical Region: Mexico.

Range
CANADA, USA, MEXICO. Stenamma diecki is the most widely distributed North American Stenamma species and was recorded by Smith (1957) from about half of United States and throughout southern Canada. In the area from the Rocky Mountains westward it is now known to occur in all States except Arizona. It also occurs in Mexico.

Snelling (1973), Wheeler and Wheeler (1986)

Biology
Backus and Herbers (2009) - Stenamma diecki is a small, cavity- and soil-dwelling ant with a widespread distribution in the US and southern Canada (Bolton et al. 2007). Its small size and cryptic habits have meant that few researchers have reported on its natural history. Cole (1940) reported that it is typically found in wet forests and Picea rubens Sarg. (Red Spruce) forests in the Great Smoky Mountains National Park. Subsequent reports have confirmed this habitat preference in populations as far north as near Montreal, PQ, Canada (Francoeur 1965, 1966; Letendre and Pilon 1972) and across the US, including Michigan (Talbot 1975) and California (Smith 1957, Snelling 1973). Where nests have been censused, worker numbers are typically low (mean worker number ranges from 31.8 per nest [Francoeur 1965] to 56.0 per nest [Talbot 1975]). Nests are generally headed by a single queen (Francoeur 1965, Letendre and Pilon 1972, Talbot 1975), although 0 queen nests are occasionally found (Letendre and Pilon 1972); polygyny seems to be absent from this species (Talbot 1975).

Systematic plot excavations in two locations have allowed us to collect data on a large number of S. diecki nests in order to examine seasonal and spatial differences in nest demography and allocation decisions within this species. Populations of this species from New York and Vermont nest in cavities far more commonly than has been reported. We found nests were monogynous at all locations, but showed considerable variation in mean queen number and mean worker number. Most nests did not produce any males or reproductive females in a season, and this pattern was also site specific. Sexual and reproductive allocation was similar for all sites tested. Finally, demographic patterns within a site over 3 seasons are consistent with those predicted by seasonal polydomy.

Smith (1957) noted the following about this species: This widely distributed species is highly adaptable to various types of ecological habitats. It can be found at altitudes at least as high as 8,000 feet. Stenamma diecki appears to be especially common in southern Canada and the most northern tier of our States. In southeastern United States (Virginia, North Carolina, and Tennessee) Stenamma diecki seems to be confined to rather high altitudes. Colonies nest in the soil and in rotting wood. Nests in the soil are usually under cover of stones, logs, humus, moss, etc. Colonies may be found nesting in boggy or swampy areas to rather dry areas and from unshaded conditions through open woods to dense woods. There appears to be only a single queen per colony. The largest colony that has come to my attention contained, on July 31, 97 workers, 98 worker pupae, 1 dealate female, 56 alate females, 28 males and 1 male pupa; the adults alone totaling 182 individuals. Data based on a number of colonies indicate that males and virgin females are produced from midsummer to early fall. Mating flights may take place from spring to fall. In the older colonies it is common for the males and virgin females produced during the current year to remain overwinter in the parental nest and take their nuptial flights in the spring or later the following year. Nests in the soil are usually shallow, seldom being more than a foot or so from the surface of the soil. There are only a few chambers. The workers are commonly of a timid disposition and on occasion will feign death when disturbed.

Cole (Tenn. Acad. Sci. J. 25:297, 1950) under the name impressum, gives an interesting account of the habitats and biology of Stenamma diecki: He studied 18 colonies found in red spruce-balsam fir forest near Newfound Gap, elevation 5,250 feet, in the Great Smoky Mountains National Park, Tennessee. The stands were not dense but the trees close enough to provide continuous dense shade; high soil moisture and low soil and atmospheric temperatures. Underbrush was exceedingly sparse but the ground was covered with decaying logs and a heavy carpet of moss. Each nest consisted of a small superficial chamber in the surface soil just beneath a stone or piece of wood. He found that when disturbed although the workers were sluggish they moved their small batches of brood to cover. Only a single egg mass was noted per nest and this mass contained from 16 to 32 eggs. Eight complete colonies consisting of 12 to 29 workers, a queen and brood were taken to ,the laboratory for further study. Males emerged from some of the colonies from August 7 to 19, but no females developed in any of the nests. Living collembolans and thysanurans were placed in the nest for food and their internal contents were devoured by the workers.

W. L. Brown and E. O. Wilson, who collected a number of colonies of Stenamma diecki in the White Mountains National Forest of Maine, made the following remarks in a letter to me,

"the Stenamma diecki colonies were taken in rotten wood and under stones at the summit of Evans Notch (a pass through the mountains) and on the east side in both dark beech woods and woods predominantly spruce-fir at somewhat lower altitudes. All localities were shaded and moist; pupae of sexes were present in many nests at this date (mid-August)and eclosed with full pigmentation a few days later in the laboratory. Other White Mountains collections were taken in mixed spruce-fir-birch forest in widely separated localities on the lower slopes on both sides of the Presidential Range. The colonies are quite abundant in many places, though inconspicuous. Few other ants are found in such situations, the most common being Formica aserva, Formica neorufibarbis, Camponotus herculeanus one or two Myrmica spp., and one or two less abundant species.

The Stenamma feign death for a short time but are quick and persistent at removing the brood to safety. The nest population of Stenamma diecki are estimated to average about 40 to 60 adult workers each in the White Mountains area. We have not been able to find nests of these or other Stenamma species at all in eastern Massachusetts though one can easily find stray workers under stones and in leaf litter during the months at the beginning of the season. We cannot account for the very striking difference in collecting between localities near Boston and those in the White Mountains.

At Evans Notch Brown and Wilson found larvae of Stenamma attached and actually feeding on a dipterous larva which was determined by W. W. Wirth as possibly an empidid. Under the same conditions but in another colony they found what they thought was a Tomocerus springtail."

Nomenclature

 *  diecki. Stenamma westwoodi subsp. diecki Emery, 1895c: 300 (w.q.) CANADA. Smith, M.R. 1957b: 161 (m.); Wheeler, G.C. & Wheeler, J. 1953b: 50 (l.). Subspecies of brevicorne: Forel, 1901e: 347. Raised to species: Creighton, 1950a: 136. Senior synonym of impressum: Smith, M.R. 1957b: 158. See also: Snelling, R.R. 1973c: 18.
 * impressum. Stenamma brevicorne subsp. impressum Buren, 1944a: 284 (w.) U.S.A. [First available use of Stenamma westwoodi subsp. diecki var. impressum Emery, 1895c: 301; unavailable name.] Raised to species: Creighton, 1950a: 137. Junior synonym of diecki: Smith, M.R. 1957b: 158.

Worker
Smith (1957) - Length 2.7-3 mm. Funicular segments 2-7 broader than long; last funicular segment approximately as long as the combined length of the two preceding segments. Eye rather small, oval, approximately 0.10 mm at its greatesc diameter and with four or five ommatidia. Thorax 0.9-0.966 mm in length from the anterior border of the pronotal collar to the apices of the epinotal spines; broadest through the prothorax (0.40-0.45 mm), narrowest through the epinotum (0.3 mm). Thoracic humeri subangular. Epinotal spines, from above, small, with acute apices, the spines approximately 0.05 mm in length but shorter than their interbasal distance. Epinotal spines, in profile, distinct but not large, subtriangular, with their apices not especially directed dorsally. In profile, mesoepinotal impression distinct but not large, scarcely 0.10 mm in length and hardly half as deep. Base of epinotum sloping posteriorly. Petiolar node, from above and behind, with dorsally converging sides and weakly rounded or almost straight superior border. Postpetiole, from above, subcampanulate, approximately 0.25 mm in length and 0.20 mm in breadth. Petiole, in profile with rather short pedicel and a subangular node. Postpetiole, in profile, varying from about as long as high to not noticeably longer than high. Gaster, 0.9 mm in length, with the first segment occupying most of the dorsal surface.

Sculpturing of head rather weakly defined, consisting of a number of small longitudinal rugulae in front which extend to the occiput or very near it, areas to the side of this more rugulose-reticulate with weakly punctulate interspaces, which are subopaque to opaque; below and median to the eye the longitudinal rugulae are very coarse. Mandible longitudinally rugulose and also with scattered punctures which in some lights appear rather coarse. Promesonotum with rather well defined, distinct and rather widely spaced longitudinal rugulae, the interspaces so feebly sculptured as to appear shining or only weakly opaquish, this depending largely upon the nature of the light; some of them form a transverse arch on the anterior border of the pronotum, especially on the pronotal collar and also dorsad of the collar. Pronotal collar largely punctulate. Base of epinotum more irregularly sculptured. Sides of the thorax, especially the meso- and metapleuron, longitudinally rugulose, the punctulate interspaces somewhat coarser on the mesopleuron. Propleuron more weakly sculptured and in some lights rather shining. Most of the dorsal surface of the postpetiolar node rather smooth and shining, the sides and extreme posterior border with rugulae and punctulate interspaces. Petiolar node a little more sculptured and therefore slightly more subopaquish than the postpetiolar node. Base of gaster with longitudinal rugulae of variable length, the longest of which are approximately 0.10 mm but which are best seen only in certain lights. Frontal area, declivity of epinotum, and gaster, rather smooth and shining. Occipital region more shining than the remainder of the head.

Body light brown to brown, the antennae and legs even lighter. Some individuals have a slight infuscation on the dorsal surface of the head and gaster (these may be a little faded due to age).

One of the cotype workers has the entire pronotum covered with very distinct, widely spaced, transverse rugulae, the interspaces punctulate but not causing the surface to be dull enough to keep from shining. Some of the cotype workers have the longitudinal rugulae on the promesonotum rather weak, not widely spaced, and the interspaces enough dull so that the entire promesonotal area is not as shining as in other workers.

The worker of diecki is perhaps one of the most highly variable of all our species of Stenamma. In Michigan, Minnesota, and southeastern Ganada, for example, the workers seem to he characterized in general by their stouter body, lighter color and stouter and more shining postpetiolar node. The postpetiolar node is commonly of a subglobular appearance. In the mountains of Tennessee and North Carolina the worker is unusually large, dark in color, and has a postpetiolar node which is Less broad in proportion to its length. The mesoepinotal impression although highly variable in size and shape is usually very large and distinct. Had I not seen so much variability in the worker of diecki throughout its general range and even in individuals from the same colony, I might be inclined to call these two variants subspecies.

Variations in workers other than cotypes from throughout the general range of diecki are as follows: Body length from approximately 2.7-3.5 mm; head longer than broad to about as broad as long, with the posterior border straight or weakly ernarginate; eye approximately 0.05-0.10 mm in its greatest diameter and usually with 4-6 ommatidia; basal teeth of mandible varying considerably in size and number but commonly with from 4-5, occasionally with 7; mesoepinotal impression highly variable in size and shape, often of a V or U shape and ranging from less than 0.10-0.166 mm in length; epinotal spines highly variable in size and also in the direction which they point, more commonly dil1ected posteriorly than upwards, approximately 0.05-0.10 mm in length; pedicel of the petiole variable in length, often short in appearance; postpetiole generally subcampanulate to subglobose in appearance; rugulae on the pronotum although usually longitudinal in direction, occasionally arched anteriorly, transverse, or irregular in direction; the density of the rugulae also highly variable; body color light brown through reddish brown to almost black but never black, appendages lighter; sides of thorax with the longitudinal rugulae and punctulate inters paces varying a great deal with regard to density and coarseness.

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

Length 3.7 mm. Eye oblong, 0.2 mm in its greatest diameter and with 14 ommatidia; anterior border of eye less than 0.2 mm from the base of the mandible. Ocelli distinct, each ocellus approximately 0.05 mm in width. Funicular segments 2-6 broader than long; last funicular segment approximately 0.3 mm in length. Thorax 1.25-1.3 mm in length from the anterior border of the pronotal collar to the apices of the epinotal spines; thoracic humeri not well defined, rounded or broadly sub angular. Epinotal spines less than 0.10 mm in length and approximately 0.3 mm apart at their apices. In profile, the thorax appears short and rather high with the base of the epinotum sloping and the epinotal declivity almost vertical. Petiolar node, in profile, subangular; postpetiolar node from the same aspect, convex above, but not strongly so.

The longitudinal rugulae on the front of the head rather fine, extending at least to the region of the ocelli. Pronotum coarsely and transversely rugulose, with weakly punctulate interspaces. Mesonotum and scutellum distinctly but less coarsely longitudinally rugulose, with punctulate interspaces. Area between the clypeal carinae, lower half of mesopleuron, and much of the dorsal surfaces of the petiolar and postpetiolar nodes smooth and shining.

Pilosity on dorsal surface of body rather abundant, grayish, composed of erect and also reclinate hairs of variable length, but largely reclinate.

Body light brown or reddish brown; mandibular teeth, eyes, borders of the ocelli and wing articulations dark.

Described from two cotype females.

Females other than cotypes vary largely in the following respects: Body length 3.4-4 mm; thoracic length 1.15-1.4 mm; head 1.12-1.2 times as long as broad, with the posterior border sometimes feebly emarginate; greatest width of eye 0.17-0.20 mm, with 12-14 ommatidia; mesonotum commonly with a longitudinat1 carina throughout its center and also with longitudinal rugulae of- variable coarseness, the entire surface of the mesonotum usually subopaque; mesopleuron variable in sculpture but usually more or less shining in appearance; epinotal spines ranging from thin to coarse, and small to fairly large, but apparently never over 0.10 mm in length; postpetiole usually longer than wide, sometimes apparently as wide as long, of a subcampanulate to globular appearance; body light brown or reddish brown to deep blackish brown but not black; antennae and legs often lighter; wings pale to yellowish with usually darker veins and stigma. Venation similar to that of brevicorne.

Although highly variable in many respects, the female is fairly constant with regard to a few characters, such as the size of the eye and the number of ommatidia therein, the nature of the sculpturing of the mesonotum and mesopleuron, and the rather smooth and shining dorsal surface of the postpetiolar node.

Male
Smith (1957) - Length 2.75•3 mm. Mandible moderately large. Ocelli not large but distinct, not placed on a prominent protuberance above the general surface of the head; anterior ocellus about 0.4 mm from the anterior border of the clypeus. Eye rather large and strongly convex, approximately 0.22 mm at its greatest diameter, the anterior border of the eye about 0.05 mm from the base of the mandible. Antennal scape rather short, about 0.25 mm in length, approximately as long as the combined lengths of the first four funicular segments; the first funicular segment enlarged, subpyriform. Thorax 1.15 mm in length from the anterior border of the pronotal collar to the junction of the thorax with the petiole; widest slightly anterior to the insertion of the wing where it is 0.6 mm; Mayrian furrows present but not always clearly seen in some lights. In profile, base of epinotum meeting the declivity on each side to form an angle or else a very small tubercle. Wings yellowish to sordid in color. In profile, petiole without an especially long peduncle, the ventral surface without a tooth or protuberance; anterior face of node meeting the dorsal surface of the node to form a rather distinct angle. From above, the postpetiole is about as broad as long, somewhat subrectangular in appearance, with the anterior portion of the sides somewhat convergent.

Mesopleuron, dorsal surfaces of petiolar and postpetiolar nodes, and gaster, smooth and shining. Much of head finely punctulate; scutellum with fine, longitudinal rugulae; epinotum punctulate and also finely rugulose; all of these areas subopaque or opaque in most lights.

Body dark brown or blackish brown but not black; mandibles, antennae, legs and apex of gaster lighter.

The description of the male is based on 14 males collected from a colony along with three workers and ten alate females at the Edwin S. George Reserve, Livingston County, Michigan, by Miss Mary Talbot on August 28, 1953, in soil on the north slope of a deep, oak,hickory woods. These individuals bear the No. 53-662.

Variations in individuals from other localities are as follows: Head 1.16-1.2 times as long as broad; anterior ocellus 0.4-0.475 mm from the anterior border of the dypeus; greatest diameter of eye 0.22-0.25 mm; scape 0.23-0.33 mm in length and as long as the combined lengths of approximately the first 4-5 funicular segments; length of thorax 1.1-1.5 mm; greatest width of thorax 0.6-0.75 mm; postpetiole frequently as broad as, or broader than long; Mayrian furrows and parapsidal sutures present but not always very distinct; prescutum propleuron, and dorsal surface of the epinotum frequently shining; body light brown through brown to black, with the mandibles, antennae, legs and apex of the gaster lighter; wings hyaline to brownish, and of the same venation as in the female.

Type Material
Near Yale, British Columbia (as reported in Smith 1957).

Snelling (1973) - Of the cotypes of Stenamma diecki I have studied two from the collections of the Museum of Comparative Zoology. The first of these bears the following labels: Stenamma/ Westwoodi/ Diecki Em/ Brit. Columbia/ Cotypes/from/ C. Emery / M.C.Z./ Cotype/ 20594. Selected here as Lectotype, this specimen has the following measurements: HL 0.80; HW 0.65; SL 0.58; PW 0.43; WL 0.90; TL 3.20; CI 81; SI 90; 01 12; OMD 1.83 x EL. The second specimen has been designated a lectoparatype and both have been returned to the MCZ. Both are in accord with the basic description of the worker caste as given by M. R. Smith (1957).

Lectotype: ; Paratype: MCZ

Etymology
Patrynom. The specimens Emery (1895) used to describe the species were collected by Dr. George Dieck.