Stenamma impar

Smith (1957) reports: In her population studies of soil nesting ants in the Droste Woods, St.Charles County, Missouri, from September to March during the years 1948 to 1953, Miss Mary Talbot found Stenamma impar to be the most common Stenamma, Stenamma schmittii second, and Stenamma meridionale third. It is surprising that no individuals of Stenamma brevicorne were taken. She is positive that in many instances she did not collect entire colonies of S. impar. Colonies or portions of colonies were collected at depths from 4 to 16 inches. Usually only one chamber was found, occasionally there were two. The largest number of workers collected from a colony was 109, the least 5. Only one mother queen was found per colony in 4 colonies. It appears from these and other records that most if not all colonies have only a single mother queen. Miss Talbot found that it is common for the larvae to overwinter in the nest; however, a half dozen or less eggs were found in 2 colonies as late as the middle of October. At the time of collection colonies were taken from both dry and damp soils. In the Edwin S. George Reserve in Livingston County, Michigan, Miss Talbot collected winged females and males from a colony on August 13, 1949. In the same locality K. Bohnsack collected 33 workers, 3 alate females and 1 male from a colony on August 19, 1949. Although Miss Talbot commonly found the species nesting in the soil, one of our records may indicate that impar also nests in rotten or faulty wood. This species has been collected at altitudes up to 4760 feet.

Identification
Smith 1957: The worker of Stenamma impar can in general be distinguished by its small size, slender form, fineness of body sculpturing, and usually light brown or yellowish brown color. Other important characters are: The rather small, coarsely faceted eye which measures approximately 0.10 mm in its greatest diameter and contains 5-6 ommatidia; funicular segments 2 through 7 broader than long; distinct to very pronounced mesoepinotal impression; the distinct but short, tuberculate spines which are angularly borne on the mesosoma; the very strikingly angular petiolar node (in profile); and the weakly developed longitudinal rugulae at the base of the gaster.

Smith cautions that worker size and color can be quite variable.

Distribution
Massachusetts to Georgia, west to North Dakota, Illinois, and Missouri (Smith 1957).

Distribution based on Regional Taxon Lists
Nearctic Region: United States.

Biology
Talbot (1957) published an account of nests found by excavating soil during the cooler months of the year in a Missouri woodland: "Workers were easy to see, for although they were small they were bright colored, were clustered in well defined chambers in firm clay soil and moved slowly when disturbed. Eight collections of complete colonies averaged 108 individuals, of which half were workers. Larvae were overwintered, and a few eggs were still present in November. Chambers were fairly deep in the soil: one was four inches below the surface, but the others ranged from seven to sixteen inches with a mean depth of 10.1 inches. A typical chamber was 1/2 inch long, 3/8 inch wide, and 1/4 inch high, dome-shaped and very smooth. Usually a colony occupied only one chamber."

Nomenclature

 *  impar. Stenamma brevicorne r. impar Forel, 1901e: 347 (w.q.) U.S.A. Smith, M.R. 1957b: 152 (m.). Raised to species: Creighton, 1950a: 137.

Type Material
From Smith (1957): Described from workers collected by A. Forel and Theodore Pergande on the Virginia bank of the Potomac River near Washington, D. C., while sifting damp leaves; also from a dealate female unassociated with other castes collected by Forel in Franklin Park, Boston, Massachusetts. I hereby designate Virginia as the type locality and have selected as a lectotype, a cotype worker from the Museum d'Histoire Naturelle Geneva, Switzerland.

Types located: Museum d'Histoire Naturelle, Geneva, Switzerland American Museum of Natural History, U. S. National Museum.

Type Locality Information
Virginia, by designation. (Smith 1957)

Etymology
Morphological. impar L. = unequal. Forel was perhaps referring to the short and uneven spines found on the propodeum.