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odorous house ant

Tapinoma sessile

What do they look like?

Ants of this genus (Tapinoma) have a flattened petiole, which is a bump on the skinny part between their abdomen and thorax, slightly covered by the base of their abdomen. Among odorous house ants, workers are all approximately the same size and shape; they are about 2.4 to 3.2 mm in length and weigh 0.35 to 0.87 mg. Workers have an oval-shaped head, a short, thick thorax, and a slightly arched body. They have a few light yellowish hairs on their mandibles (appendages near their mouth), the front of their head, and near their hips. Their body is deep brown or black, and their mandibles and appendages are lighter. Queens are larger, at 3.75 to 4.3 mm in length; they have a square head, large eyes, and stout antennae when compared to the workers. Queens also have brown to black bodies, with a lighter thorax and abdomen. When they have wings, they are gray with yellow-brown veins. After mating, queens lose their wings. Males and queens have a similar shape and size, males are about 3.60 to 4.44 mm in length. They also have large, noticeable genitalia. Their body is deep brown to almost black, while their appendages are sometimes lighter. (Botz, et al., 2003; Smith, 1928)

Eggs are subelliptical in form and pearly white in color, measuring 0.24 by 0.39 mm. They become more opaque as they get closer to hatching. Larvae are the size of the egg when they first hatch, and grow to about 0.72 by 1.74 mm. As they grow, their head starts to curve. Their body is segmented and yellowish, and becomes very plump and thick when full grown. They also have a distinct bump on their bodies near their tail. Pre-pupae look like full grown larvae, measuring about 1.8 mm in length. As they start to reach the pupal stage, their skin becomes dry and wrinkles. Pupae do not have cocoons; they are naked and white, with no markings and are typically 1.82 to 2.29 mm in length. After a couple days, their eyes begin to turn brown then black, as their mandibles also turn brown and their body begins to turn shades of yellow. After coming out of pupation, it takes a few days for adult ants to attain full color. (Botz, et al., 2003; Smith, 1928)

  • Range mass
    0.00035 to 0.00087 g
    0.00 to 0.00 oz
  • Range length
    2.4 to 4.4 mm
    0.09 to 0.17 in

Where do they live?

Odorous house ants (Tapinoma sessile) are native to the Nearctic region and are one of the most widespread ant species in North America. In the United States, these ants are found in all 48 continental states and have also recently been found in Hawaii. Their range also extends into southern Canada and northern Mexico. (Buczkowski, 2010; Buczkowski, 2012)

What kind of habitat do they need?

Odorous house ants build their nests in a wide variety of mild habitats and locations. They are found in urban and natural areas, and nest from sea level to over 4,000 meters in elevation. In natural areas, they live in forests, meadows, grasslands, riparian areas, bogs, pastures, and sandy areas along coasts. They also nest in areas that have experienced natural disturbances, such as areas that have recently flooded. They build their shallow nests under leaf litter, matted grass, in dried cow dung, in above-ground cavities in trees, beneath stones, and in rotten logs and stumps. In urban areas, they nest in city parks, backyards, and almost any disturbed area, such as in and around buildings, and in mulch and debris piles. Nests are rarely out in the open in urban areas, and are usually close to man-made structures. (Buczkowski and Bennett, 2008a; Buczkowski, 2010; Buczkowski, 2012; Menke, et al., 2010; Milford, 1999; Smith, 1928)

  • Range elevation
    0 to 4000+ m
    0.00 to ft

How do they grow?

Odorous house ants go through an egg, larvae, pupae, and adult stage. Eggs are laid from late April until cold weather begins, usually in November. Eggs hatch after 11 to 26 days. The larval stage takes 13 to 29 days, the prepupal stage takes 2 to 3 days, and the pupal stage lasts anywhere from 8 to 28 days, averaging about 14 days in the summer. Following their molt from pupae to adult, they enter a callow stage that lasts anywhere from 2 days to several weeks before they become fully-functioning adult ants. Their total developmental time depends on the time of year that the eggs are laid. Eggs laid in April to June, have a total development time of 5 to 9 weeks. Eggs laid from June to September, take 6 to 7 weeks to develop. Eggs laid later in the season spend the winter as larvae, taking up to 6 to 7 months to complete development. Winged females are present in the nest by mid-June or July, while males appear a little earlier, which suggests that the eggs that develop into mating ants are typically laid early in the season. In indoor nests, when temperatures remain warm year-round, egg laying likely also occurs year-round. (Smith, 1928)

How do they reproduce?

There is little information available about the mating habits of odorous house ants. Mating likely takes place both inside and outside the nest. Winged females appear in the middle of June or July, males appear shortly before. Mating takes place during this time and males die shortly afterward. (Smith, 1928)

Colonies might not produce breeding ants until they are well-established. Queens can lay up to 20 or 30 eggs in a day, but average around 1 to 2 eggs per day. In a season, a queen in an urban colony averages about 350 eggs. This might vary based on the number of queens present in the nest. While urban nests have many queens, nests in natural habitats typically only have one queen. In outdoor nests, egg-laying occurs through most of the season, from April until October or November. In indoor nests, where temperatures remain warm throughout the winter, egg laying takes place year-round. Workers tend to the queens by giving general care and regurgitating food. Workers can lay eggs without mating; unfertilized eggs normally develop into males. These eggs take longer to reach maturity, at about 11 to 12 weeks. (Smith, 1928)

  • How often does reproduction occur?
    Odorous house ants only breed once.
  • Breeding season
    Mating occurs in the middle of summer, while egg-laying occurs from early spring to fall.
  • Average eggs per season

Among odorous house ants, workers give a significant amount of brood care, as do many ant species. When relocating, or when their nest is disturbed, workers carry the broods from nest to nest. Workers feed the brood by regurgitating liquid food from mouth to mouth. They also lick and clean the brood, and help larvae when molting into prepupae. Males die shortly after mating and therefore do not provide any parental care. Likewise, queens do not provide any care either. Once the offspring develop into adults, brood care stops and they join the colony. (Buczkowski and Bennett, 2008a; Smith, 1928)

  • Parental Investment
  • female parental care
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

How long do they live?

In natural conditions, queens likely live a year or longer, while workers likely live several months to a year or more. Males die about 1 week to 10 days after mating. (Smith, 1928)

  • Typical lifespan
    Status: wild
    3 to 12+ months

How do they behave?

Odorous house ants nest in both natural and urban areas. Colonies of odorous house ants are only active from April to October in natural habitats, but they are active year round in heated buildings and homes. These ants are active day and night and forage on well-established trails at any hour of the day. Unlike many ant species, odorous house ants do not divide their labor or establish worker castes. All workers perform all tasks, including brood care, foraging, and moving the contents of the nest from one location to another. In natural areas, odorous house ants live peacefully with many other ant species. However, in urban areas, colonies dominate resources and tend to exclude other species. Workers aggressively defend their territory from other ant species in urban areas. Individuals usually fight alone, and do not attack with their nest mates. This is likely because the defensive chemicals they release also serve as alarm pheromones, so nest mates tend to flee when they encounter these chemicals, rather than joining in. Likewise, when a nest is disturbed, chaos ensues and ants run in a rapid jerky motion and may also elevate their abdomens. (Buczkowski and Bennett, 2008a; Buczkowski, 2010; Fellers, 1987; Klotz and Reid, 1992; Smith, 1928)

Odorous house ants have an unusual flexible colony structure that changes between urban and natural habitats. In natural habitats, colonies are typically small and only have 1 queen. These colonies live peacefully in the same area as other ant species. In urban areas, these ants form supercolonies, with many nests per colony and many queens per nest. Nests are usually close together, and no aggression is shown between ants from different nests. This allows odorous house ants to become a dominant species and a pest species. Nests move frequently, changing locations as quickly as 21 days. Colonies reproduce by budding. The number of nests tends to change throughout the year; most of the colony overwinters in a central location, in one or a few nests. As soon as the temperature increases, the number of nests rapidly grows, peaking during the summer and remaining steady until late fall, when the number drops. While nests may move frequently, colonies can use the same overwintering and nesting sites for years. (Buczkowski and Bennett, 2008a; Buczkowski, 2010)

Home Range

While nests move often, colonies of odorous house ants tend to nest in the same places from year to year, and nest locations are usually nearby. Foraging trails between nests range from 10 to 50 feet long, ants rarely stray from these trails. (Buczkowski and Bennett, 2008a; Smith, 1928)

How do they communicate with each other?

Odorous house ants forage on well established trails. They primarily use odor trails, but visual cues, such as light sources, and tactile cues are also important. These ants tend to follow structural guidelines, such as grooves in the pavement and ridges in surfaces, especially when they forage in the dark. Having trails that they can follow using different senses is useful for an ant species that forages both during the day and at night. Trails are rarely in open areas; in urban habitats, trails often follow man-made structural guidelines. They identify their nest mates using hydrocarbons on their cuticles. They use their antennae to detect these hydrocarbons, as well as other odors and chemicals in the environment. Their ability to identify nest mates is important because they form large colonies with many nests. They can identify colony members from distant nests, and do not become aggressive. Their lack of inter-nest aggression is important for their success. Defensive chemicals produced by odorous house ants serve as the colony alarm pheromone. These ants become agitated and erratic when they find a fighting nest mate; they release defensive chemicals and run away, rather than joining the fighting. (Buczkowski and Bennett, 2008a; Buczkowski and Bennett, 2008b; Klotz and Reid, 1992)

What do they eat?

Odorous house ants are omnivorous. A significant part of their diet is made up of a secretion produced by aphids, scale insects, and membracids, known as honeydew. These ants also feed on nectar and tree sap. Odorous house ants prey on insects and spiders that are less than 4.0 mm in length. They also consume vertebrate carrion when it is available. Odorous house ants feed "opportunistically" in urban areas and will eat nearly any available human food. They have a preference for sweets, and will eat sugar, honey, butter, and ice cream, as well as non-sweet foods, such as beef, fish, potatoes, cheese, and milk. Odorous house ants bring prey back to the nest or store foods such as honeydew in their crop. When they return, they regurgitate the liquid food mouth to mouth to colony members that do not forage. (Buczkowski and VanWeelden, 2010; Buczkowski, 2012; Clark and Blom, 1991; Fellers, 1987; Klotz and Reid, 1992; Smith, 1928)

  • Animal Foods
  • carrion
  • insects
  • terrestrial non-insect arthropods
  • Plant Foods
  • nectar
  • sap or other plant fluids

What eats them and how do they avoid being eaten?

Odorous house ants are often preyed upon by several bird species, including northern flickers (Colaptes auratus), black-billed magpies (Pica hudsonia), chimney swifts (Chaetura pelagica), American crows (Corvus brachyrhynchos), red shafted flickers (Colaptes cafer collaris), and house sparrows (Passus domesticus). Toads of genus Bufo also prey on these ants. Larval antlions consume odorous house ants that fall into their pits. To defend themselves, odorous house ants secrete defensive chemicals and are physically aggressive towards predators and other ant species. (Botz, et al., 2003; Buczkowski and Bennett, 2008b; Gow, et al., 2013; Smith, 1928)

What roles do they have in the ecosystem?

In natural areas, odorous house ants form small colonies near the nests of other ant species, although they are never the dominant species. However, in urban areas, odorous house ants become dominant, and are found near few other species. They form large colonies that include many nests; their nests may include many individuals, which are able to out-compete other ant species for resources. Even though they are a native species, they can be invasive in urban areas. Recently, they have been found in Hawaii, where they may become an invasive species. Odorous house ants have an advantage over many other species because they can live in altitudes as high as 4,000 meters. Odorous house ants are often found in the same areas as Argentine ants, a significant invasive species. They are often studied together, because although one is native and one is invasive, they have a similar biology, body-structure, behavior, and colony makeup. Both species also colonize areas disturbed by human activity, and are household pests. They also tend many of the same aphid species. Argentine ants tend to out-compete odorous house ants for most resources, especially food sources. These species are very aggressive towards each other, and although odorous house ants can win one-on-one fights, large groups of Argentine ants can easily dominate groups of odorous house ants. (Buczkowski and Bennett, 2008a; Buczkowski, 2010; Buczkowski, 2012; Powell, et al., 2009)

Odorous house ants farm honeydew-producing insects, as honeydew is an important part of their diet. In exchange for the honeydew, ants protect the honeydew producers from predators and parasitoids. They form these mutualistic relationships with many insects, including membracids (Vanduzeea segmentata and Entylia sinuata), aphids (Aphis gossypii, Toxoptera aurantii, Periphyllus negundinis, Ceruraphis viburnicola, Anuraphis cardui, Myzus cerasi, Macrosiphum solanifollia, Lipaphis pseudobrassicae, and other members of genus Aphis), scale insects (members of genus Kermes, Chionaspis furfura, Coccus hesperidum, Planococcus citri, and Pseudococcus maritimus), and butterfly larvae (Callophrys irus). Many insect species also live in their nests, since these species do not benefit odorous house ants, these relationships are not mutualistic. This includes species of crickets (Myrmecophilus oregonensis, Myrmecophilus manni and Myrmecophilus nebrascensis), wingless wasps (Isobrachium myrmecophilum), rove beetles (Staphylinidae, Zyras tapinomatis, Mymoecia lugubris, and Nototaphra lauta), springtails (Collembola), termites (Isoptera), and pill bugs (Armadillidium). (Albanese, et al., 2007; Buczkowski, 2012; Powell and Silverman, 2010; Powell, et al., 2009; Smith, 1928)

Species (or larger taxonomic groups) that are mutualists with this species

Do they cause problems?

Odorous house ants are significant pests to homes and buildings throughout much of North America. They often nest in mulch, debris piles, or inside buildings. Because these ants maintain such large colonies in urban areas, it is difficult to get rid of them. Pesticides and baits may kill a few nests, but other nearby nests can easily re-colonize the area. The widespread use of pesticides may also remove competing ant species from their area, which may benefit the odorous house ants. With the competition removed, colonies of odorous house ants are free to move into the area. The landscaping trend of placing mulch outside buildings attracts the ants to urban areas. Their population can be controlled by removing or replacing the mulch. Odorous house ants also tend many aphid species that can be crop pests. By maintaining and protecting these aphid populations from predators and parasites, odorous house ants indirectly cause crop and other plant damage. (Buczkowski, 2012; Meissner and Silverman, 2001; Powell and Silverman, 2010; Powell, et al., 2009; Scharf, et al., 2004; Smith, 1928)

  • Ways that these animals might be a problem for humans
  • household pest

How do they interact with us?

There are no known positive effects of odorous house ants on humans.

Are they endangered?

Odorous house ants have no special conservation status.

Some more information...

Odorous house ants get their common name from the distinct odor produced by their anal gland when they are killed or crushed. Reportedly this odor smells like coconuts. (Smith, 1928)


Angela Miner (author), Animal Diversity Web Staff, Leila Siciliano Martina (editor), Animal Diversity Web Staff.


Albanese, G., M. Nelson, P. Vickery, P. Sievert. 2007. Larval feeding behavior and ant association in frosted elfin, Callophrys irus (Lycaenidae). Journal of the Lepidopterists' Society, 61/2: 61-66.

Botz, J., C. Loudon, J. Barger, J. Olafsen, D. Steeples. 2003. Effects of Slope and Particle Size on Ant Locomotion: Implications for Choice of Substrate by Antlions. Journal of the Kansas Entomological Society, 76/3: 426-435.

Buczkowski, G. 2010. Extreme life history plasticity and the evolution of invasive characteristics in a native ant. Biological Invasions, 12/9: 3343-3349.

Buczkowski, G. 2012. The odorous house ant, Tapinoma sessile (Hymenoptera: Formicidae), as a new temperate-origin invader. Myrmecological news, 16: 61-66.

Buczkowski, G., G. Bennett. 2008. Aggressive interactions between the introduced Argentine ant, Linepithema humile and the native odorous house ant, Tapinoma sessile. Biological Invasions, 10/7: 1001-1011.

Buczkowski, G., G. Bennett. 2008. Seasonal polydomy in a polygynous supercolony of the odorous house ant, Tapinoma sessile. Ecological Entomology, 33/6: 780-788.

Buczkowski, G., M. VanWeelden. 2010. Foraging Arena Size and Structural Complexity Affect the Dynamics of Food Distribution in Ant Colonies. Environmental Entomology, 39/6: 1936-1942.

Clark, W., P. Blom. 1991. Observations of Ants (Hymenoptera: Formicidae: Myrmicinae, Formicinae, Dolichoderinae) Utilizing Carrion. Southwestern Naturalist, 36/1: 140-142.

Fellers, J. 1987. Interference and Exploitation in a Guild of Woodland Ants. Ecology, 68/5: 1466-1478.

Gow, E., K. Wiebe, R. Higgins. 2013. Lack of diet segregation during breeding by male and female Northern Flickers foraging on ants. Journal of Field Ornithology, 84/3: 262-269.

Klotz, J., B. Reid. 1992. The use of spatial cues for structural guideline orientation in Tapinoma sessile and Camponotus pennsylvanicus (Hymenoptera, Formicidae). Journal of Insect Behaviour, 5/1: 71-82.

Meissner, H., J. Silverman. 2001. Effects of aromatic cedar mulch on the Argentine ant and the odorous house ant (Hymenoptera : Formicidae). Journal of Economic Entomology, 94/6: 1526-1531.

Menke, S., W. Booth, R. Dunn, C. Schal, E. Vargo, J. Silverman. 2010. Is It Easy to Be Urban? Convergent Success in Urban Habitats among Lineages of a Widespread Native Ant. PLOS ONE, 5/2: e9194. Accessed October 15, 2013 at

Milford, E. 1999. Ant Communities in Flooded and Unflooded Riparian Forest of the Middle Rio Grande. Southwestern Naturalist, 44/3: 278-286.

Powell, B., R. Brightwell, J. Silverman. 2009. Effect of an Invasive and Native Ant on a Field Population of the Black Citrus Aphid (Hemiptera: Aphididae). Environmental Entomology, 38/6: 1618-1625.

Powell, B., J. Silverman. 2010. Impact of Linepithema humile and Tapinoma sessile (Hymenoptera: Formicidae) on three natural enemies of Aphis gossypii (Hemiptera: Aphididae). Biological Control, 54/3: 285-291.

Scharf, M., C. Ratliff, G. Bennett. 2004. Impacts of residual insecticide barriers on perimeter-invading ants, with particular reference to the odorous house ant, Tapinoma sessile. Journal of Economic Entomology, 97/2: 601-605.

Smith, M. 1928. The biology of Tapinoma sessile Say, an important house-infesting ant. Annals of the Entomological Society of America, 21: 307-330.

University of Michigan Museum of ZoologyNational Science Foundation

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Miner, A. 2014. "Tapinoma sessile" (On-line), Animal Diversity Web. Accessed May 18, 2024 at

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