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thief ant

Solenopsis molesta

What do they look like?

Thief ants are small. Workers are pale yellow and 1.5 to 1.8 mm long. Their antennae have 10 joints and a large antennal club. Queens are larger, at 4 to 5 mm long. They are the same shade of yellow, with a darker brown color on their head, prothorax (their first body segment), and in between their abdominal segments. Their antennae have 11 joints and the same antennal club. Before mating, queens have two pairs of glossy wings, and after mating, they lose their wings. Males are also larger than workers, although they are smaller than queens, at 3.5 to 3.6 mm long. Their legs and antennae are yellow, while their body is brown. Eggs are pearly white, and become clear just before hatching. They are elliptical and 0.25 mm long. Larvae are white, and covered in double-hooked hairs. Their posterior end is large, while their anterior end is smaller and tapered. Their body is curved, although that decreases as the larva grows. Worker and reproductive pupae are not found inside cocoons, and they can be told apart by their body size, worker pupae are the smallest and queen pupae are the largest. All thief ants are white during their early stages, and later change to adult colors. (McColloch and Hayes, 1916; Smith, 1965; Thompson, 1990)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • Range length
    1.5 to 5.0 mm
    0.06 to 0.20 in

Where do they live?

Thief ants (Solenopsis molesta) are native to the Nearctic region. They are found throughout the United States, although they are most common in the eastern half of the country. They have been reported as far south as the middle of Mexico, although they are probably rare in that region. (Grundmann and Peterson, 1953; McColloch and Hayes, 1916; Pecarevic, et al., 2010; Wetterer, et al., 2001; Zenger and Gibb, 2001)

What kind of habitat do they need?

Thief ants usually live in fields and meadows, although they can also nest in urban and suburban areas. They can live in turfgrass habitats, such as golf courses and lawns, as well as grassy areas in cities, such as on the medians of major roads. They can also be found in agricultural fields. They build their nests in the ground, either out in the open or under rocks. The openings to their nests are usually a distance from the nest itself, with many underground tunnels and small chambers packed with solid walls. Thief ants can also build nests inside homes, in basements, under baseboards, or in building foundations. (DuBois and DuBois, 1994; Grundmann and Peterson, 1953; McColloch and Hayes, 1916; Pecarevic, et al., 2010; Zenger and Gibb, 2001)

How do they grow?

Thief ants undergo complete metamorphosis, which means they go through an egg, larvae, pupa and adult stage. Eggs hatch in about 16 to 28 days. Larvae are fed and tended by workers while they go through several development phases, known as instars. In total, the larval stage lasts for about 21 days; their final instars, known as semi-pupae, last 2 to 11 days. Any larvae still in the nest when temperatures drop have longer development times. Their pupal stage lasts 13 to 27 day, after which, they enter the callow stage for 2 to 3 days, where they resemble an adult but are helpless and lack pigment. Finally, they become a fully-functioning adult. Workers need at least 52 days to develop, from egg to adulthood. (DuBois and DuBois, 1994; McColloch and Hayes, 1916)

How do they reproduce?

Thief ants mate during nuptial flights, which include hundreds to tens of thousands of males and females. These flights take place during the afternoon, from about 4 to 6 pm, usually during July to September. They mate in air. Some females even carry workers during the flight, and these workers in turn, likely go with the queen to form a new colony. When the males and females separate after mating, females move to a new colony, and males die shortly afterward. (DuBois and DuBois, 1994; McColloch and Hayes, 1916; Thompson, 1990; Wilson and Hunt, 1966)

Immediately after mating, females fly aimlessly in big swooping paths, after which, queens form new colonies. First, they look for a good large area, such as a lawn or field, then they look for smaller areas to shelter under, such as a grass stem, a clump of earth, or a leaf. They crawl beneath the object and stay there. Most queens begin their colony without workers, and their first batch of eggs develops into workers. However, some queens carry workers during the nuptial flight, which become the workers in the new colony. Queens lay eggs 3 days after mating, and may lay as many as 105 eggs in a single day. Most colonies have a single queen, although some have multiple, one nest in particular had 26 queens. (DuBois and DuBois, 1994; McColloch and Hayes, 1916)

  • How often does reproduction occur?
    Thief ants only mate once.
  • Breeding season
    Mating takes place from late July to September.

Similar to other ant species, worker thief ants give significant care to all stages of the brood. Workers feed larvae by trophallaxis, which means they regurgitate food and transfer it mouth to mouth. Workers also help remove waste excreted by larvae just before molting and pupal skin, when pupae molt into adults. After developing into adults, they enter a callow stage, where they are weak and helpless, during this time, workers provide aid and carry them as needed. Once they have fully developed into adults, the ants join the colony and brood care stops. When queens form new colonies, they often do not have workers. In these cases, queens care for their young themselves. In addition to providing nutrients in the eggs, queens also produce unfertilized eggs to feed the larvae. (DuBois and DuBois, 1994; McColloch and Hayes, 1916)

  • 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 laboratory colonies, most queens generally do not survive more than two months, this is likely due to their small body size and tendency to dry out. In natural habitats, queens likely live over a year. Males die shortly after mating, living only a few days to weeks as adults. Workers likely live a few months. (DuBois and DuBois, 1994; McColloch and Hayes, 1916)

  • Typical lifespan
    Status: wild
    1 (high) years
  • Average lifespan
    Status: captivity
    2 months

How do they behave?

Thief ants received their common name because they often nest in, or near other ant's nests, and steal their broods. Thief ants are very sneaky; they move without being noticed, partially because they are very small. They are not usually aggressive towards other ant species, they usually avoid or run away from other species, this is probably one of the reasons they are such successful brood thieves. Their nests are connected to the nests they rob by galleries that are too small for the other ant species, but big enough for the tiny worker thief ants to move freely. Thief ants usually have small colonies, with several hundred to a couple thousand workers. They are aggressive toward other thief ants from distant nests. All tasks are done by workers, and much of their activity is under-ground. Most foraging takes place in the afternoon, when temperatures are warmest, but they also forage throughout the day and night if temperatures are warm enough. (McColloch and Hayes, 1916; O'Neal, 1974; Rao and Vinson, 2009; Vinson and Rao, 2004; Vogt, et al., 2004)

Home Range

Their home range is likely just the area around their nest as well as any nearby nests from which they can steal broods. (McColloch and Hayes, 1916)

How do they communicate with each other?

When thief ants first come into contact with other ants, whether it is a nest mate or another species, they use their antennae to antennate the other individual. Their antennae sense odors and chemicals so they can identify nest mates. Thief ants from far away nests are aggressive towards one another, which suggests that the chemicals are specific to their nests. Their antennae are used to sense odors and chemicals and feel their environment. Thief ants can release a long-lasting, effective chemical from their poison gland when thieving from other nests. This chemical prevents other ants from tending and protecting their brood, allowing thief ants to easily steal the brood. When invading red imported fire ant's nests, thief ants remain undetected, possibly by mimicking their colony odors, allowing thief ants to sneak in and move about without drawing attention. (Rao and Vinson, 2009)

What do they eat?

Thief ants are omnivorous. They prey on a large variety of insect eggs and larvae, through under-ground foraging. The broods of other species are a significant portion of their diet, as they steal from nests. They also eat vegetables, seeds, fruits, and honeydew, and even scavenge dead insects. Populations in urban and suburban environments eat human-produced foods including meats, breads, sweets, animal fat, and dairy products. Thief ants are also sometimes called 'grease ants', as they are commonly seen eating grease. (McColloch and Hayes, 1916; Rao and Vinson, 2009; Smith, 1965; Vinson and Rao, 2004; Zenger and Gibb, 2001)

  • Animal Foods
  • insects
  • Plant Foods
  • seeds, grains, and nuts
  • fruit

What eats them and how do they avoid being eaten?

Predators of thief ants include spiders, Texas horned lizards, skink species, and other species of ants including Crematogaster lineolata and soldier ants. To defend themselves, thief ants release chemicals from their venom glands. Once the venom is released, ants are usually more likely to run away from a threat than fight. (Jones, et al., 1979; McColloch and Hayes, 1916; Rao and Vinson, 2009)

What roles do they have in the ecosystem?

Their nests are often found near the nests of many other ant species. Thief ants sneak in to other nests and steal broods. One species they regular interact with are red imported fire ants. Thief ants remain undetected when they sneak in to rob broods, and can destroy a small colony of 30 to 60 workers, as they also prey on workers and queens. Red imported fire ants may avoid nesting in areas with a high density of thief ants. Unlike many other native ant species, thief ants seem mostly unaffected by invasive ant species, and can nest in invaded areas, while many other ant species cannot. In addition to nesting near red imported fire ants' nests, thief ants can also nest in areas colonized by Argentine ants, which normally displace all native ant populations. Thief ants can co-exist with other species, partially because they live underground and can forage at different times of day, which allows them to avoid most invasive species. Thief ants farm a few species of honeydew-producing insects. In exchange for eating honeydew, the ants protect the insects from predators and parasitoids. These species include scale insects of genus Dactylopius, and aphids including Geoica squamosa, Aphis seteriae, Aphis middletoni, Antoninoides nortoni, Anuraphis maidiradicis, and Smynthurodes betae. Ectoparasitic mites of genus Hypoaspis have been found on workers, queens, and males. Thief ants may also be an intermediate host of poultry tapeworms, as they may carry tapeworm segments into their nests. (Landis, 1967; McColloch and Hayes, 1916; Pecarevic, et al., 2010; Smith, 1965; Vinson and Rao, 2004; Wetterer, et al., 2001; Landis, 1967; McColloch and Hayes, 1916; Pecarevic, et al., 2010; Smith, 1965; Vinson and Rao, 2004; Wetterer, et al., 2001)

Species (or larger taxonomic groups) that are mutualists with this species
Commensal or parasitic species (or larger taxonomic groups) that use this species as a host
  • mites (Hypoaspis)
  • poultry tapeworms (Raillietina tetragona)

Do they cause problems?

Thief ants caused crop damage in the early 1900's, especially to sorghum crops, typically by feeding on and destroying seeds. As late as 1959, they were referred to as the most harmful insect to sorghum, though there is very little mention of crop damage since then. Likewise, by tending and protecting honeydew-producing insects that can be agricultural pests, they can cause further crop damage. Thief ants can nest in homes and other buildings, and often invade during warm weather. They can nest in cracks and crevices, under floorboards, in basements, and in the interior of walls. Due to their small size, they are difficult to keep out, and can easily slip in spaces to feed on food stored in pantries and kitchens. Thief ants are considered one of the "Dirty 22" pest species by the United States Food and Drug Administration. The "Dirty 22" is a list of the most common pests that spread foodborne diseases. However, pharaoh ants may be misidentified as thief ants. Pharaoh ants are a much more significant nuisance than thief ants. Additionally, thief ants may be an intermediate host of poultry tapeworms. (Burkhardt, 1959; Grundmann and Peterson, 1953; Landis, 1967; McColloch and Hayes, 1916; Smith, 1965; Sulaiman, et al., 2012; Thompson, 1990; Vinson and Rao, 2004)

How do they interact with us?

Thief ants prey on many pest species, providing a natural control method, including southern masked chafers and Japanese beetles. These species are turfgrass pests, which can destroy large areas of grass in suburban and urban areas. Thief ants eat the eggs and larvae of these and other white grub species. They also feed on many agricultural pests, including black cutworms, all stages of maize billbugs, larvae of stalk borers, larvae of Hessian flies, pupae of corn-ear worms, and larvae of white-marked Tussock moths. However, since thief ants can also be can be pests, they are not effective for controlling pest populations. Thief ants can also invade and destroy small colonies of red imported fire ants, which can be household pests and inflict painful stings. (McColloch and Hayes, 1916; Vinson and Rao, 2004; Zenger and Gibb, 2001)

  • Ways that people benefit from these animals:
  • controls pest population

Are they endangered?

Thief ants have no special conservation status.

Some more information...

In addition to the common name thief ants, they are also known as grease ants or sugar ants. (Thompson, 1990)

Contributors

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

References

Burkhardt, C. 1959. Increasing sorghum stands in field test by controlling thief ants and other insect pests. Journal of Economic Entomology, 52/3: 365-368.

DuBois, B., M. DuBois. 1994. Colony founding by queens of Solenopsis molesta (Hymenoptera: Formicidae). Entomological News, 105/2: 61-68.

Grundmann, A., B. Peterson. 1953. House infesting ants in Salt Lake City, Utah. Journal of the Kansas Entomological Society, 26/2: 59-60.

Jones, T., M. Blum, H. Fales. 1979. Synthesis of unsymmetrical 2,5-di-normal-alkylpyrrolidines - 2-Hexyl-5-pentylpyrrolidine from the thief ants Solenopsis molesta, Solenopsis texanas, and its homologs. Tetrahedron Letters, 12: 1031-1034.

Landis, J. 1967. Attendance of Smynthurodes betae (Homoptera: Aphididae) by Solenopsis molesta and Tetramorium caespitum (Hymentopera: Formicidae). Annals of the Entomological Society of America, 60/3: 707.

McColloch, J., W. Hayes. 1916. A preliminary report on the life economy of Solenopsis molesta Say. Journal of Economic Entomology, 9: 23-38.

O'Neal, J. 1974. Predatory behavior exhibited by three species of ants on the imported fire ants: Solenopsis invicta Buren and Solenopsis richteri Forel. Annals of the Entomological Society of America, 67/1: 140.

Pecarevic, M., J. Danoff-Burg, R. Dunn. 2010. Biodiversity on Broadway - Enigmatic Diversity of the Societies of Ants (Formicidae) on the Streets of New York City. PLOS ONE, 5/10: e13222. Accessed November 02, 2013 at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0013222.

Post, D., R. Jeanne. 1982. Rate of exploitation of arboreal baits by ants in an old-field habitat in Wisconsin. American Midland Naturalist, 108/1: 88-95.

Rao, A., S. Vinson. 2009. The Initial Behavioral Sequences and Strategies of Various Ant Species During Individual Interactions With Solenopsis invicta. Annals of the Entomological Society of America, 102/4: 702-712.

Smith, M. 1965. House-infesting Ants of the Eastern United States: Their recognition, biology and economic importance. Washington D.C.: United States Department of Agriculture.

Sulaiman, I., M. Anderson, D. Oi, S. Simpson, K. Kerdahi. 2012. Multilocus Genetic Characterization of Two Ant Vectors (Group II "Dirty 22" Species) Known To Contaminate Food and Food Products and Spread Foodborne Pathogens. Journal of Food Protection, 75/8: 1447-1452.

Thompson, C. 1990. Ants that have pest status in the United States. Pp. 51-67 in R Vander Meer, K Jaffe, A Cedeno, eds. Applied Myrmecology: A World Perspective. Boulder, Colorado: Westview Press, Inc.

Vinson, S., A. Rao. 2004. Inability of incipient Solenopsis invicta (Hymenoptera : Formicidae) colonies to establish in a plot with a high density of Solenopsis (Diplorhoptrum) colonies. Environmental Entomology, 33/6: 1626-1631.

Vogt, J., J. Reed, R. Brown. 2004. Temporal Foraging Activity of Selected Ant Species in Northern Mississippi during Summer Months. Journal of Entomological Science, 39/3: 444-452.

Wetterer, J., A. Wetterer, E. Hebard. 2001. Impact of Argentine ant, Linepithema humile on the native ants of Santa Cruz Island, California. Sociobiology, 38/3B: 709-718.

Wilson, E., G. Hunt. 1966. Habitat Selection by the Queens of Two Field-Dwelling Species of Ants. Ecology, 47/3: 485-487.

Zenger, J., T. Gibb. 2001. Identification and impact of egg predators of Cyclocephala hirta and Popillia japonica (Coleoptera : Scarabaeidae) in turfgrass. Environmental Entomology, 30/2: 425-430.

 
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Miner, A. 2014. "Solenopsis molesta" (On-line), Animal Diversity Web. Accessed October 20, 2017 at http://www.biokids.umich.edu/accounts/Solenopsis_molesta/

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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