Meet the Odorous House Ant

Editor’s note: This information is reprinted from Techletter by Pinto & Associates. To learn more about the biweekly Techletter, visit

www.techletter.com or call 301/884-3020.

The odorous house and, Tapinoma sessile, is a major ant pest throughout the United States. In areas where it occurs with the Argentine ant, however, the Argentine ant tends to displace the odorous house ant. Odorous house ants and Argentine ants look similar. Both are mainly outdoor species but become a problem when they forage, and sometimes nest, indoors.

OHA workers are very small, less than 1/8-inch long, brown in color and without a sting (but they can bite). There is a single flattened node that is hidden between the thorax and abdomen. You can tell the difference between the OHA and the Argentine ant by the smell of crushed workers. The odorous house ant gets its name because it has a smell similar to rotten coconuts when crushed. The Argentine ant has a stale, musty odor. When alarmed, the OHA runs in an erratic manner with its abdomen raised.

Outside nests of the OHA are shallow and are found in soil, mulch, under rocks, stones, logs, boards and other objects on the ground. They also nest in other diverse sites like under bark, in plant holes, trash piles, animal nests, under siding, behind bricks, etc. A typical nest consists of a main colony and several satellite colonies, each with a queen and brood. Ants indoors may be foraging in from outside nest sites. They follow a chemical trail from the colony so you may be able to track them back to the nest.

When the OHA nests indoors, nests are usually found near a moisture source and a food source, most often in kitchen areas. Typical sites are in wall voids or behind paneling, behind baseboards or window sills near hot water heaters or pipes, and under carpets or flooring. Nests are moved frequently, complicating control. The indoor nest may be connected to other secondary nests outside.

OHAs are sweet feeders, usually feeding on the honeydew produced by plant-feeding insects like aphids. They also feed on plant nectar and live and dead insects. Inside they will feed on a wide variety of foods but especially sweets like sugar, pastries and syrup.

Control of this ant is difficult, usually requiring a combination of methods, including a perimeter treatment. Finding and treating the nests directly is the best control. Because they prefer sweets, OHAs will usually accept sweet baits, especially liquid baits.

_______

OHA Fast Facts

Order/Family:
Hymenoptera/Formicidae Scientific Name: Tapinoma sessile (Say)

Workers are brown to black and 1⁄16- to 1⁄8-inch long

The thorax has no spines, and the petiole has one segment which, when viewed from above, is hidden by the rest of the abdomen

There is a slit at the tip of the abdomen instead of a circlet of hairs

The best identifying characteristic is the "rancid butter" or "rotten coconut" smell these ants produce when they are crushed

Swarm to mate from early May through mid-July. They also mate in the nest, forming new colonies by "budding" off the original colony

A colony has about 10,000 workers and several queens, each laying one egg a day

They usually invade structures during rainy periods after honeydew on plants has washed off

Source: PCT’s Technician’s Handbook