Odorous House Ant

Appearance

"T. sessile" is a small ant that ranges in color from brown to black, and varies in length from ​1⁄16 to ​1⁄8 inches. When crushed, these ants leave a smell which leads to their nickname "stink ant".

The gaster portion of the abdomen sits directly on top of the petiole in the abdomen of this species, which helps distinguish them from other small, dark, invasive ants.

Their antennae have 12 segments.

Distribution

"T. sessile" is native to North America and ranges from southern Canada to northern Mexico, but is less common in the desert southwest.

Behavior

Colonies vary in size from a few hundred to tens of thousands of individuals. Big colonies usually have multiple queens.

The odorous house ant is tough: Injured workers have been observed to continue living and working with little hindrance, some queens with crushed abdomens still lay eggs, and there are documented instances of "T. sessile" queens surviving without food or water for over two months. They also appear highly tolerant to heat and cold. These ants are difficult to remove from a home after their colony has become well-established.

When offered a choice of food sources, the ants preferred sugar and protein over lipids, and this preference persisted in all seasons. When specific sugar sources were studied the ants preferred sucrose over other sugars, such as fructose or glucose.It was also found that this ant species practices seasonal "polydomy" to have access to multiple food sources. The colony will overwinter in a single nest, and then during spring and summer when resources are more abundant they will form multiple nests. This allows them to better use food sources, that might be spread out. During the winter they will return again to the same nest location. Seasonal polydomy is rather rare, and only found in 10% of all polydomous species. Seasonal polydomy is not found in many ant species, but there are many ant species, including "T. sessile", which move within a season: Migration to better forage sites is common.

Seasonal activity patterns of the ants were also studied, and corresponding to the seasonal polydomy, it was observed that the ants displayed the most activity between March and September and displayed almost no activity from October to December. Daily activity patterns were also studied. In March "T. sessile" foraged during the day, but in April that pattern changed and the ant began to forage during both day and night. During most of the summer, "T. sessile" shows low levels of activity throughout the day and night.

Habitat

"T. sessile" can be found in a huge diversity of habitats, including within houses. They forage mainly for honeydew, which is produced by aphids and scale insects that are guarded and tended by the ants, as well as floral nectar and other sugary foods. They are common household pests and are attracted to sources of water and sweets.

Reproduction

The queens lay the eggs which incubate between 11–26 days. After hatching, the larval stage lasts between 13–29 days, and the pre-pupal and pupal stages last between 10–24 days. Little is known about the lifespan of the ant, though it has been shown that queens live at least 8 months, workers at least a few months, while males appear to live only approximately a week.

Food

Foragers collect food that is around the nest area and bring it back to the colony to share with the other ants. "T. sessile" has polydomous colonies, meaning that one colony has multiple nests. Because of this, "T. sessile" is very good at foraging for food when there is great variance in the distribution of resources. Instead of going back to a faraway nest to deliver food, they move workers, queens, and the brood to be closer to the food, so that they can reduce the cost in effort of food transport. This is called 'dispersed central-place foraging'. It was also found that the half-life of the stay at any one nest was about 12.9 days.

Buczkowski and Bennett also studied the pattern of food movement within a nest. They labeled sucrose with Immunoglobin G proteins, and then identified them using an enzyme-linked immunosorbent assay to track the movement of food. They found that food was spread through "trophallaxis". Despite this trophallactic spread of food, the workers kept most of the sucrose. They also found that some queens received more food than others, suggesting a dominance hierarchy even between queens. They also found that the nests were located in a system of trails, and that their distribution depended on where food was found and the distance between these patches of food. It was also found that the rate of trophallactic feeding depends on the number of ants per nest, and the quality of food available. When the number of donors is kept constant, but the number of total individuals in increased, more individuals test positive for the food marker. This indicates that more individuals are eating, but the amount they eat is less. If the number of donors was doubled, and the size of the overall population increased, the number of individuals receiving food more than doubled, again indicating that the number of individuals fed increased, but that the per capita amount of food consumed decreased.

When searching for food, primary orientation is when ants are exploring a new terrain without the guidance of odor trails. Secondary orientation is when terrain has been explored, and there are pre-existing odor trails which ants use to orient themselves. When "T. sessile" ants are orienting themselves for the first time they often rely on topography. The major types of elements they rely on are bilaterally elevated, bilaterally depressed, unilaterally elevated, and unilaterally depressed. They use these types of surfaces to orient along, and lay the first odor trails, which can then be followed in the future, to the food source, by other ants.

Predators

Some birds and toads will eat odorous house ants on occasion.

Wheeler mentions "Bothriomyrmex dimmocki" as a possible parasite of odorous house ant colonies, suggesting that "B. dimmocki" queens invade and replace "T. sessile" queens.

"Isobrachium myrmecophilum" appears to parasitize odorous house ants.