Formica sessilis Say, 1836:287; _.
Tapinoma sessilis: F. Smith, 1858:57.
Tapinoma boreale Roger, 1863:165; o _. Mayr, 1866:497; o.
Formica gracilis Buckley, 1866:158; o _.
Formica parva Buckley, 1866:159; o.
Tapinoma sessile: Mayr, 1886b:434. Emery, 1895:332; o _.
M. Smith, 1928:309; pl. 18 figs 1?3; o _ _. M. Smith, 1947:596;
pl. 17 fig. 65; o. Creighton, 1950:352, 353; pl. 48; o _ _. Gregg,
1963:443?447; map; o. Wheeler and Wheeler, 1963:157?160; map 28;
o _ _. Wheeler and Wheeler, 1973:106?107; o _ _. Allred, 1982:506?
507. Wheeler and Wheeler, 1986:58.
RANGE: Southern Canada and entire United States; Lower
DESERT RECORDS. Map 9. Inyo Co.: S. end Owen's Lake, 26
May 1974 (M. S. & J. S. Wasbauer; CDFA); sand dunes, 1150',
Valley, 8 July 1976 (DG; LACM); Salt Lake, 1060', Saline Valley,
23 Mar 1976 (DG; LACM); 3/4 mi N, 3/4 mi W Badwater Spg., 2200',
Inyo Mts. 15 June 1976 (DG; LACM); Willow Creek, 2400', Inyo
Mts., Mar?Sept 1976 (DG; LACM); Pat Keys Cyn., 3000', Inyo Mts.,
14 June 1976 (DG; LACM); Craig Cyn., 3400', Inyo Mts., 18 Sept
1976 (DG; LACM); Hunter Cyn., 2000'?2800', Inyo Mts., 2 Apr 1976
(DG; LACM); Paiute Cyn., 3500'?5000', Inyo Mts., 17 June 1976 (DG;
LACM). San Bernardino Co.: Saratoga Spg., O', DVNP, 28 May 1955
(J. N. Belkin, et al.; LACM). Riverside Co.: Andreas Cyn., 1500',
4 mi S Palm Springs, 20 Nov 1969 (GJW, #Cal.842; GJW); Deep Canyon,
1000'?1100', various dates (GJW; #Cal.472, 473, 718, 765, 824;
GJW); Whitewater Canyon, 26 July 1963 (E. I. Schlinger; LACM). San
Diego Co.: Grapevine Cyn., 4.5 mi W Hwy. 78, 2220 ft., 2 Apr 1997
(R. A. Johnson; RAJC); Sentenac Cyn., 2400 ft., 23 Apr 1952 (WSC;
DISCUSSION. The record from Saratoga Spring might seem
questionable were there not records of Hypoponera and Brachymyrmex
from the same site. These are evidently relict populations dating
from the Tertiary. At least some of the samples from the Inyo Mts.
might represent similar populations.
Widespread in North America, T. sessile is an easily
recognized ant which can be confused only with L. humile. The
strongly convex propodeum and less pungent odor when crushed will
distinguish L. humile. Since it is often a house pest, T. sessile
has been fairly well studied, especially by M. Smith (1928, 1965).
This species is extremely adaptable and therefore can be
found in a broad range of habitats. In the California desert it
has been collected at elevations from O' to 6300' in streamside
habitats with cottonwood, along desert washes with palo verde,
catsclaw, etc. and in Pinon?juniper communities. Although nests
are predominantly found under stones, this species is also known
to locate under loose bark, in cavities of plant stems, in wasp
galls, in bird and mammal nests and under leaves and rubbish
Colony size is variable depending on age, but may range from
2000 to 10,000 ants, with numerous queens. Mating usually takes
place within the nest between siblings with occasional mating
flights outside. Alate females have been collected from desert
localities during the month of May.
This species is primarily aphidicolous and coccoidicolous
and an extensive list of aphid and coccoid associations is
presented by M. R. Smith (1928). Workers also collect nectar
from floral and extrafloral nectaries of plants and occasionally
take living and dead insects as food. They forage singly from
trails and are active during both day and night.
Predators of T. sessile include birds (crows, red?shafted
flickers) and toads (Bufo spp.).
Various myrmecophiles have been found in nests of this ant.
They include: Myrmecophila spp. (Orthoptera), Zygras, Myrmoecia,
Nototaphra, Connophron, and Myrmedonia (Coleoptera).