Subfamily DOLICHODERINAE
Tribe DOLICHODERINI

Tapinoma sessile (Say)

Tapinoma sessile, full face view of worker
(click photo to enlarge).
Tapinoma sessile, profile view of worker
(click photo to enlarge). .
Tapinoma sessile, profile view of worker
(click photo to enlarge).
Tapinoma sessile, profile view of worker with arrow pointing to the flattened petiole (click photo to enlarge).

Introduction
Tapinoma sessile is commonly called the odorous house ant. This native ant is one of the most adaptable species of ants in the United States. It is widespread and common throughout the country and nests in a wide variety of habitats including sandy beaches, pastures and fields, forests, wet areas (such as bogs) and houses or other buildings. 

Identification
Odorous house ant workers are 2.4-3.25 mm in overall length and colored uniformly brown to blackish-brown.  The single petiolar node, found between the alitrunk and gaster, is flattened, rather than erect and is usually concealed by the gaster. Tapinoma sessile may be confused with Linepithema humile, the Argentine ant, which is approximately the same size and color.  Tapinoma sessile differs by having the petiolar node flattened, whereas the node is erect in the L. humile

Biology and Economic Importance
These ants lack a stinger, but are capable of biting, although the bite is minimal due to the small size of the ant.  Workers of this species emit a rotten coconut-like odor from the anal glands, which can be smelled by crushing live individuals.  When freshly crushed, L. humile individuals have a different smell and emit a stale, greasy or musty odor, instead of the rotten coconut-like smell of T. sessile.  Argentine ants are generally seen in very large numbers on a regular basis, compared to the more sporadic occurrence of odorous house ants. 

Typically, nests are in the soil beneath rocks and stones, bricks, logs, boards or other objects on the ground, but they are also known to nest under the bark of stumps and logs, in plant cavities, insect galls, trash piles, in animal nests, under mulch in flower beds, in stacks of firewood, under shingles or siding, behind ivy or other vines on external walls, behind brick veneer, in wall voids, and in many other locations.  Nests in the soil are generally indefinite and may be difficult to spot.  This pest also has the habit of moving its nest site every few weeks, which can make control more challenging.  Colony size is quite variable and may range from several hundred to many thousands of individuals.  As with Argentine ants, colonies contain numerous reproductive queens.  Also like the Argentine ant, different odorous house ant colonies do not attack one another, but can live in relative closeness in peace with one another. 

In Mississippi, mating usually occurs from early to mid May, while in more northern states, mating would typically occur later in the summer.  Mating can take place in the nest itself between the males and their "sister" females (reproductive queens), or there may be nuptial flights with males and reproductives flying away from the nest to mate.  In some cases, females leave the nest independently or travel with a small number of workers to aid them in new colony establishment. 

In natural habitats, T. sessile workers are noted for their love of honeydew produced by various insects such as scale insects, plant lice, mealybugs, and membracid planthoppers.  They eat the honeydew as well as attend those insects to further promote honeydew production and protect them against attack by predators.  Additionally, workers regularly feed on sweet plant secretions from the nectaries of flowers.  Although their dietary favorites in the wild are sweets, they also feed on both live and dead insects and a variety of other things.  In households, T. sessile feed on a wide variety of foods including both raw and cooked meats, vegetables, dairy products, pet foods, fruits, and because they are sweet-feeding ants, they are especially attracted to sugar, sweetened cereals, pastries, syrup, etc.  As a result of their preference for sweets, odorous house ants will readily take sweet baits, especially liquid baits, and baits can be useful in their control. 

In homes, odorous house ants are most commonly found in the kitchen/pantry area, but they can occur anywhere in the house where there is an attractive food source, such as where pet food is stored.  Because, these ants primarily nest outdoors, indoor infestations are likely to be linked to outdoor colonies.  Foraging ants lay a chemical trail from the colony to the food source, and with a little patient effort, these trails can often be identified and followed back to the nesting site.  Tapinoma sessile workers may be recognized by their foraging behavior; they usually travel in files or lines and are very active and fast.  When excited or alarmed, workers can be observed moving around in an excited and erratic manner. 

Distribution
Southern Canada, United States (except desert areas of the southwest), to Mexico (Creighton 1950; Smith 1965). This species is known from all of the southeastern states including AL, AR, FL, GA, LA, MS, NC, SC, T N (MacGown, 2009).

Literature Cited
Creighton, W.S. 1950. The Ants of North America. Bulletin: Museum of Comparative Zoology 104: 1-585.

MacGown, J. A. 2009. Pest Ants of the Southeastern United States. Online at: http://www.mississippientomologicalmuseum.org.msstate.edu/Researchtaxapages/Formicidaepages/faunal.lists
/SE.pest.ants.htm. Accessed Feb 19, 2009.

Smith, M. R. 1965. House-infesting ants of the Eastern United States, their recognition, biology, and economic importance. United States Department of Agriculture, Technical Bullitin No. 1326: i-105.

Links

AntWeb
Discover Life Images

Wikipedia entry: http://en.wikipedia.org/wiki/Tapinoma_sessile

MEM Publication on Odorous House and Argentine Ants.
Layton, B. and J. A. MacGown. 2006. Control of Argentine Ants and Odorous House Ants in the Home.  Mississippi State University Extension Service, Publication no. 2407. 7 pp.