Stenamma brevicorne (Mayr)

Submitted by David on Thu, 09/09/2010 - 00:57
Genus Species: 
Stenamma brevicorne
Biology
Biology Introduction: 

From Smith (1957): Stenamma brevicorne is not only one of the most widely distributed but the oldest and perhaps best known of our North American species of Stenamma. Although apparently preferring to nest in wooded areas, the species is also found in meadows and other places. It usually nests in moderately dense to dense woods of such composition as maple, mixed oaks, oak-maple, red and white oaks, and beech-maple. Here the ants more commonly nest in the soil under stones, logs, humus, moss or other debris, as well as in the rotting wood of logs and stumps. Colonies are small, consisting of only a few dozen to a hundred or so adult individuals. The largest that has come to my attention was found at Tiffin, Ohio, on August 21, 1948, by Talbot and Headley and was composed of 105 workers, 8 alate females, and 12 males. Although no one has made a detailed study of Stenamma brevicorne, random observations indicate that this species is timid and sluggish, subterranean or hypogaeic. The workers are undoubtedly carnivorous, but may also be predaceous. Wheeler, so far as I am aware, was the first individual to advance the theory that, in some colonies at least, winged females and males overwinter in the parental nest, these sexual castes having been produced from late summer to early fall. None of the evidence I have seen disproves this, but no doubt the age of the colony has a great deal to do with whether or not sexual castes can be produced. As the colonies are not large, it is likely that there is only one mother queen per colony. This also seems to be the case in many, if not most of our own species. The overwintering sexual castes apparently start emerging from the parental colony in spring or early summer of the following year. It is believed that it is then that mating and the forming of new colonies are started. H. V. Weems, Jr., captured a copulating male and female on May 14, 1950. Since alate females have been captured at light traps and males taken while flying at dusk, it appears that both castes fly freely at night, like many other ants. Although altitudunal records are lacking for Stenamma brevicorne, it appears that this form lives in low lands or areas of only moderately high elevation.

Additional Biology: 

Talbot (1965) offers the following observations about Stenamma brevicorne from Missouri:

Stenamma brevicorne, together with Lasius flavus, seemed the most typical ant of the low field habitat. It was common and widespread here (23 colonies on 18 plots), but had been collected only once before on the Reserve (at swamp edge). Three other species of Stenamma (S. impar, S. diecki, S. schmitti) present on the Reserve did not live in the field.

Stenamma brevicorne workers foraged over the ground in cool damp weather, and the finding of workers just below the surface indicates that they also foraged below ground in the crumbly topsoil. Nest entrances were simply small openings hidden among leaves and grasses, and were not found unless workers were seen entering them. An attempt was made to collect whole colonies; therefore nests were dug completely when possible. This was not always a successful process, but the general pattern of nest structure seemed clear. Usually there was a chamber within 2 inches of the surface, which might be empty during dry weather. Some nests appeared to have no chambers in the crumbly surface soil but started with a chamber 4 inches down in more solid clay. No colony had more than 4 chambers, and most had only 2. Lowest chambers ranged in depth from 3 to 13 inches, with most at 6 inches. Large colonies dug down to soil moisture, while small colonies did not. Chambers were surprisingly large and were often only partly filled with brood. Those measured ranged from 1/2 X 1/2X 1/4 in. to 1 1/2 X 1 1/2 X 1 in. with most being larger than an inch in diameter and a half inch high. The range of size of the 10 most complete population counts is recorded in Table II. Eggs, larvae and worker pupae were present from before June 23, when the first colonies were dug, through the rest of the summer, although the September 10 colony had only one worker pupa. Twelve colonies which had winged adults or winged pupae averaged 20.6 alates per colony, of which 11.2 were females and 9.4 were males. Winged pupae were found in colonies from July 9 to August 11, and adults from August 10 to September 10 when observations ceased. It is known that S. brevicorne has flights in the spring (Smith, 1957; Kannowski, 1958). It may also fly in the late fall when conditions are right.

This species generally inhabits open areas, with either a soil nest that opens underneath an object resting on the ground or within the litter horizon in debri or other objects where they can aggregate within chamber like structures.

Identity
Identification: 

The worker of Stenamma brevicorne may be distinguished by its moderately large eye, which usually bears 8-10 ommatidia in its greatest diameter; the strong mesoepinoraI impression which is frequently twice as long as deep; base of epinotum usually with a transverse welt following the mesoepinorai impression; the distinct spines which are approximately one-fourth to one-third the length of the base of the epinotum; petiolar node subconical, when viewed from behind; postpetiolar node, from above, stout, as broad as, or broader than long; head, thorax, petiole and postpetiole subopaque; promesonotum largely coarsely longitudinaIly rugulose; body usually brown with the gaster light at the base and apex and darker medianly.

Smith 1957

Etymology Text: 

Presumably brevi L., short and corn L., horn, are a reference to the spines on the propodeum.

Occurrence
Range: 

This species is distributed from at least Nova Scotia, Quebec, and Ontario south to Tennessee and west to Nebraska and Minnesota.

From Smith 1957 and contemporary collections.

Region: 
Nearctic
Type Information
Type Information: 

Described by Mayr from workers and alate females collected by Theodore Pergande from beneath a stone in a locality presumably near Washington, D.C. 

The Gustav Mayr collection in the Naturhistorisches Museum in Vienna Austria. A cotype worker and female are in the U. S. National Museum as well as two workers and four females apparently belonging to the original series.

Smith 1957

Syntypes: AMNH, NHMW

Type Locality: 

Virginia. USA.