Animal Diversity Web

Ge­o­graphic Range

Formica ob­scuripes, the west­ern thatch­ing ant, is na­tive to the Nearc­tic re­gion. It is wide­spread across the west­ern half of Canada and the United States. Its range ex­tends as far south as Ari­zona and New Mex­ico, and as far east as Michi­gan and Mis­souri. In the south­ern half of Canada, it can be found from British Co­lum­bia to Man­i­toba. It is es­pe­cially preva­lent in the Pa­cific North­west. (Crutsinger and Sanders, 2005; Hig­gins and Lind­gren, 2012; Risch, et al., 2008; Tilman, 1978; Weber, 1935)

• Biogeographic Regions
• nearctic
  • native

Habi­tat

Formica ob­scuripes builds its nests in semi-arid re­gions, such as dry grass­lands, in­clud­ing shrub-steppe habi­tats and sage­brush, prairies, conif­er­ous forests, dunes, and alpine mead­ows. Nests are also often found in areas of sec­ondary suc­ces­sion. Formica ob­scuripes can live in a large range of al­ti­tudes. Nests have been found as low as 800 m and as high as 3,194 m, though the most com­mon al­ti­tudes are be­tween 1,524 to 2,743 m. Nests are built into the ground, often around a struc­ture, such as the main stem of a sage­brush plant or even a fence post. Nests can ex­tend up to 4 feet into the ground and are typ­i­cally con­structed out in the open. The west­ern thatch­ing ant gets its name from a mound of "thatch" that the work­ers as­sem­ble on top of the nest. This thatch con­sists of twigs, grasses, plant parts, and soil, and can be any­where from a few cen­time­ters to a meter high. The ther­moreg­u­la­tory abil­i­ties of the thatch allow the nests to be ex­posed to a va­ri­ety of tem­per­a­tures, hu­mid­ity, and weather con­di­tions. Sec­ondary nests are often con­structed at the base of plants where Formica ob­scuripes farms hon­ey­dew. (Beat­tie and Cul­ver, 1977; Con­way, 1996a; Crutsinger and Sanders, 2005; Hig­gins and Lind­gren, 2012; McIver and Steen, 1994; Mico, et al., 2000; Risch, et al., 2008; Tilman, 1978; Weber, 1935)

• Habitat Regions
• temperate
• terrestrial

• Terrestrial Biomes
• desert or dune
• savanna or grassland
• forest

• Range elevation

  800 to 3194 m

  2624.67 to 10479.00 ft

Phys­i­cal De­scrip­tion

Formica ob­scuripes has one peti­ole and colony mem­bers may have a va­ri­ety of col­ors and sizes. There is a con­tin­u­ous size dis­tri­b­u­tion in work­ers, gen­er­ally rang­ing from 4.0 to 7.5 mm in length, mak­ing it dif­fi­cult to group the work­ers by size. Head width ranges from 0.94 to 2.1 mm, show­ing sig­nif­i­cant vari­a­tion. Work­ers can be grouped into major and minor or major, media, and minor work­ers. Due to the large vari­a­tion in size, these ants are likely poly­mor­phic. Work­ers typ­i­cally have a red­dish-or­ange head, the tho­rax can be ei­ther red­dish-or­ange or black, and the ab­domen is black. Legs and an­ten­nae can be red­dish-or­ange or black. Re­pro­duc­tive forms also fol­low this col­or­ing. Smaller work­ers can also be all black or dark brown. Eggs are creamy white, and el­lip­ti­cal shaped. They are about 0.6 mm long and 0.31 mm wide. Lar­vae are the same size as the egg when they hatch and grow to about 6.0 mm in length. Re­pro­duc­tive pupae are 9 mm in length, while worker pupae are 3.5 to 7.0 mm in length. (Bil­lick and Carter, 2007; Fraser, et al., 2001; Her­bers, 1979; Weber, 1935)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry
• polymorphic

• Range length

  4.0 to 7.5 mm

  0.16 to 0.30 in

De­vel­op­ment

Formica ob­scuripes is holometabolous. The first batch of eggs is laid in April. Eggs are laid through­out the sum­mer, until as late as the mid­dle of Au­gust. Eggs are laid in a brood cham­ber, as well as other soil cham­bers, where they de­velop and are tended to by adult work­ers. Eggs hatch after 23 to 53 days. Lar­vae can be found in brood cham­bers of the nests from the be­gin­ning of June to the end of Au­gust, and pu­pate after 7 to 33 days. Pupae that de­velop into sex­ual forms are not pre­sent in the nests after June, but those that de­velop into work­ers can be found into early Sep­tem­ber. They re­main pupae for 31 to 93 days, be­fore de­vel­op­ing into adults. By fall, the brood cham­ber has emp­tied. Total time of de­vel­op­ment from egg to adult takes 61 to 122 days. (Weber, 1935)

• Development - Life Cycle
• metamorphosis

Re­pro­duc­tion

Mat­ing takes place dur­ing nup­tial flights for Formica ob­scuripes dur­ing June and July. Prior to tak­ing flight, re­pro­duc­tive in­di­vid­u­als live in the nest. Re­pro­duc­tive fe­males are ob­served from the end of June to mid-Au­gust, while males are pre­sent from the end of June to July. When leav­ing the nest for flight, winged fe­males are often roughed up by work­ers. Work­ers tug on the fe­male's wings and an­ten­nae with their mandibles. Flights occur in the morn­ing and typ­i­cally take place on clear, warm, wind­less days. The par­tic­i­pants often climb nearby struc­tures be­fore tak­ing flight. Nup­tial flights may in­volve a few, to sev­eral hun­dred in­di­vid­u­als, who fly to nearby swarm­ing grounds. The same swarm­ing ground may be used from year to year. Fe­males land on plants or grass and perch near the top, with their ab­domen stick­ing up in the air. They likely re­lease a pheromone at this point to help males find them. Males fly around and swarm, at­tempt­ing to find fe­males. While wait­ing, fe­males may move their bod­ies and an­ten­nae, pos­si­bly as a vi­sual in­di­ca­tor of their lo­ca­tion. When they find a fe­male, males at­tach to them, mate and re­main mo­tion­less for 1 to 5 min­utes until one of them moves, then the male drops off. Males fly off and fe­males re­main for a lit­tle while. If sev­eral males find a sin­gle fe­male, they fight until one wins and mates, while oth­ers drop to the ground. Nup­tial flights con­tinue each day until the nest is emp­tied of all alates. Colonies can have 5 to 16 flights. (Con­way, 1996b; Con­way, 1996a; Tal­bot, 1972)

• Mating System
• eusocial

While there has been a large amount of re­search con­ducted con­cern­ing the nup­tial flights of Formica ob­scuripes, very lit­tle is known about what oc­curs af­ter­wards. Since colonies move nests or grow by bud­ding, it is un­cer­tain where fe­males that have re­cently mated in the nup­tial flights go next. They likely re­turn to al­ready es­tab­lished nests to lay their eggs. Colonies of Formica ob­scuripes typ­i­cally have two or more wing­less queens that lay eggs. The num­ber of queens pre­sent may vary sig­nif­i­cantly, as one colony was recorded as hav­ing 198 queens. The first brood of eggs is laid in the nest in April by queens al­ready pre­sent in the nest. The eggs are laid in spe­cial brood cham­bers where they un­dergo meta­mor­pho­sis and are cared for by work­ers. (Con­way, 1996b; Con­way, 1996a; Her­bers, 1979; Weber, 1935)

• Key Reproductive Features
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
  • internal
• oviparous

• Breeding interval

  Females mate once during the nuptial flight, while males may mate several times.

• Breeding season

  Nuptial flights occur in June and July.

Colonies of Formica ob­scuripes ex­hibit sig­nif­i­cant brood care. Dur­ing the sum­mer, a large brood cham­ber is con­structed near the base of the thatch. This cham­ber is di­vided by twigs that are poked through at all an­gles and is well in­su­lated. Pupae can be found in the upper part of the cham­ber, while eggs and lar­vae are in the lower part of the cham­ber, as well as in lower cham­bers in the soil. The small­est work­ers re­main in the nest to care for and feed the brood. Once they reach adult­hood, ants be­come in­de­pen­dent and join the colony as work­ers or sex­ual forms. The en­tire brood has left the cham­ber by the be­gin­ning of fall and the cham­ber is then filled with thatch. There is also pro­vi­sion­ing in the eggs pro­vided by the queen. (Her­bers, 1979; Weber, 1935)

• Parental Investment
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • female

Lifes­pan/Longevity

Most work­ers live 19 to 44 days after reach­ing adult­hood, an av­er­age of 31.6 days, though some over­win­ter and live more than a year. (Con­way, 1996a)

• Range lifespan
  Status: wild

  1+ (high) years

• Typical lifespan
  Status: wild

  19 to 44 days

Be­hav­ior

Like most ant species, Formica ob­scuripes lives in large colonies. A large colony may have any­where from 10,000 to 40,000 in­di­vid­u­als. It is di­ur­nal and for­ages dur­ing the day. In the warmer parts of its range, F. ob­scuripes is ac­tive year round, while in the north­ern re­gions it over­win­ters in its nest and is ac­tive from April until Oc­to­ber or No­vem­ber. The sex­ual males and fe­males are able to fly, while work­ers are wing­less. There are con­flict­ing re­ports about the role of dis­crete worker castes in the colony. Some re­searchers say F. ob­scuripes lacks dis­crete castes, while oth­ers have ob­served 2 or 3 dis­tinct castes. In size, work­ers are on a con­tin­u­ous scale, with a large va­ri­ety of sizes, though there are no ob­vi­ous group­ings. Work­ers are often grouped into major, media, and minor work­ers. Major work­ers re­pair the nest and thatch, as well as for­age for in­sect prey to bring back to the nest. Ma­jors often work to­gether to take down large in­sects. These at­tacks may last as long as 30 min­utes. When at­tack­ing prey singly, major work­ers snatch the in­sect in their mandibles and im­me­di­ately re­turn to the nest. Media work­ers trans­port broods be­tween nests, for­age for veg­e­ta­tion, and farm aphids. Mi­nors are rarely seen out­side the nest and likely take part in brood care and tend the queens. All castes clean the nest. None of these tasks are ex­clu­sively per­formed by any one caste and all sizes con­tribute when nec­es­sary, which likely sup­ports the idea that there are no dis­crete castes. (Bil­lick and Carter, 2007; Con­way, 1996b; Con­way, 1997; Crutsinger and Sanders, 2005; Heikki­nen, 1999; Her­bers, 1979; Tilman, 1978; Weber, 1935)

West­ern thatch­ing ants get their name from the piles of thatch they con­structs to cover their nest mounds. The thatch is cre­ated from seeds, twigs, plant stems, grass, and soil. Piles of thatch can be sev­eral cen­time­ters to a meter deep and sev­eral cen­time­ters to 1.5 m across. This thatch keeps nests at a con­stant tem­per­a­ture through­out the day, even though nests are typ­i­cally con­structed out in the open in dry, warm re­gions. Work­ers are con­stantly re­pair­ing and adding to the thatch. Many mounds are also built around the main stem of plants such as sage­brush. Ants chew the bark on the stem and spray formic acid at it until it dies, at which point it can be re­moved, cre­at­ing a cen­tral pas­sage in the cen­ter of the nest. Formica ob­scuripes is poly­do­mous, with one colony typ­i­cally liv­ing in sev­eral mounds. Colonies often switch pri­mary nests. New colonies are formed by bud­ding. Sec­ondary mounds may be­come pri­mary nests, or new mounds may be cre­ated nearby, with work­ers mov­ing be­tween the mounds. (Con­way, 1996a; Con­way, 1997; Her­bers, 1979; McIver and Steen, 1994; Mico, et al., 2000; Weber, 1935)

Mound usage by the colony can change through­out the day and year. A nest can have any­where from 1 to 52 en­trances, and these en­trances con­stantly change. Dur­ing warmer parts of the day, ants use en­trances that are under cover and use en­trances that are in the sun dur­ing the morn­ing and evening. The same prin­ci­ple ap­plies to trail usage. Most trails are con­structed under cover of veg­e­ta­tion, rarely veer­ing out into the open. Ants will also re­main in the nest or sec­ondary nest dur­ing the hottest part of the day, with most for­ag­ing tak­ing place dur­ing the morn­ing and evening. Many colonies have sec­ondary nests. These nests are typ­i­cally con­structed at the base of the plants where work­ers farm aphids. Work­ers use this sec­ondary nest through­out the day, the largest num­ber take shel­ter in the mid-af­ter­noon dur­ing the warmest tem­per­a­tures. There are two types of work­ers in­volved in hon­ey­dew farm­ing, ten­ders and trans­porters. Trans­porters spend much of the day in the sec­ondary nest, while the ten­ders farm hon­ey­dew and bring the hon­ey­dew to the trans­porters. The trans­porters col­lect the hon­ey­dew in their crop from the ten­ders and re­turn to the nest with the hon­ey­dew. (Con­way, 1996a; Con­way, 1997; Her­bers, 1979; McIver and Steen, 1994; Mico, et al., 2000; Weber, 1935)

• Key Behaviors
• flies
• diurnal
• motile
• sedentary
• hibernation
• colonial

Home Range

Formica ob­scuripes tends to stay close to the nest; one study showed that plants far­ther than 20 m away from the nest were not vis­ited by the ants. Mound den­sity in some areas is 115 mounds/ha. In one study, the clos­est mounds were 2.36 m, while an­other study showed nests were usu­ally sep­a­rated by more than 100 m. (Con­way, 1996a; Hig­gins and Lind­gren, 2012; Tilman, 1978)

Com­mu­ni­ca­tion and Per­cep­tion

An­ten­nae are one of their most im­por­tant sen­sory or­gans, used for ol­fac­tion, chem­i­cal de­tec­tion, and tac­tile per­cep­tion. Formica ob­scuripes com­mu­ni­cates with other work­ers by an­ten­na­tion and also per­ceives their en­vi­ron­ment with their an­ten­nae. Ant crick­ets (Myrme­cophilus manni) live in Formica ob­scuripes nests and have learned to mimic their an­ten­nae move­ments, which al­lows crick­ets to an­ten­nate with ants and re­main un­de­tected as non-colony mem­bers. When for­ag­ing at extra flo­ral nec­taries, ants can com­mu­ni­cate with other for­agers. If an ant finds a de­pleted nec­tary, it leaves a drop of liq­uid at the junc­tion of the main stem and the stem to the de­pleted nec­tary. When an­other ant moves along the stem, it will an­ten­nate the drop of liq­uid and move past the de­pleted nec­tary with­out hav­ing to in­ves­ti­gate it­self. Fe­males re­lease pheromones into the air dur­ing mat­ing to at­tract males. As males swarm over the plants where the fe­males wait, fe­males also move their body and an­ten­nae to sig­nal their lo­ca­tion, in­di­cat­ing that vi­sion is im­por­tant in per­ceiv­ing other in­di­vid­u­als. (Con­way, 1996b; Hen­der­son and Akre, 1986; Tal­bot, 1972; Tilman, 1978)

• Communication Channels
• visual
• tactile
• chemical

• Other Communication Modes
• pheromones

• Perception Channels
• visual
• tactile
• chemical

Food Habits

Formica ob­scuripes is an om­ni­vore. It preys on many species of in­sects, par­tic­u­larly or­thopter­ans, bee­tles, ter­res­trial isopods, hemipter­ans, lep­i­dopteran lar­vae, dipter­ans, and other ants. It also scav­enges dead in­sects and other in­ver­te­brates. For­ag­ing ants bring both liv­ing and dead in­sects back to the nest. Formica ob­scuripes also eats or­ganic mat­ter, nec­tar from extra flo­ral nec­taries, and plant tis­sues in­clud­ing leaves, galls, and flow­ers. It has been recorded scav­eng­ing seeds, eat­ing the ed­i­ble part and stor­ing the rest in the nest. Oc­ca­sion­ally, these ants also feed on car­rion, such as dead rat­tlesnakes, birds, and small mam­mals. Ants typ­i­cally col­lect liq­uid from the car­casses and store it in their crops, re­turn­ing to the nest and re­gur­gi­tat­ing the liq­uid via trophal­laxis. Formica ob­scuripes also farms hon­ey­dew from hon­ey­dew-pro­duc­ing in­sects, in­clud­ing aphids and mem­bracids. Hon­ey­dew is an im­por­tant com­po­nent of their diet, as a sig­nif­i­cant source of amino acids, car­bo­hy­drates, and water. It pro­vides en­ergy for the work­ers, and nu­tri­ents for the brood and queen. These ants oc­ca­sion­ally also prey on the in­sects that they tend. (Beat­tie and Cul­ver, 1977; Bil­lick and Carter, 2007; Clark and Blom, 1991; Con­way, 1997; Er­ick­son, et al., 2012; Heikki­nen, 1999; McIver and Yan­dell, 1998; McIver, et al., 1997; Tilman, 1978)

• Primary Diet
• omnivore

• Animal Foods
• carrion
• insects
• terrestrial non-insect arthropods

• Plant Foods
• leaves
• seeds, grains, and nuts
• nectar
• flowers

• Other Foods
• detritus

Pre­da­tion

There are a va­ri­ety of preda­tors of Formica ob­scuripes. As preda­tors them­selves, they are ag­gres­sive and de­fend their brood and the aphids that they tend. They can spray formic acid when threat­ened or at­tacked. Other in­sects that gain entry to the nest can pose a threat to the brood. Ant crick­ets usu­ally live peace­fully in the nest, but have been ob­served at­tack­ing lar­vae. An­other ant species, Lep­totho­rax hir­ti­cor­nis, may eat lar­vae if it gets in the nests and will also at­tack and eat iso­lated work­ers. Many species of spi­ders are also preda­tors. Many bird species, in­clud­ing east­ern king­birds, west­ern king­birds, flick­ers, and Amer­i­can crows feed on Formica ob­scuripes. Toads are also preda­tors, in­clud­ing Cana­dian toads and Wood­house's toads. Bears have also been known to dig open nests to feed. (Con­way, 1996a; Con­way, 1997; Heikki­nen, 1999; Hen­der­son and Akre, 1986; McIver, et al., 1997; Weber, 1935)

• Known Predators

  • ants (Leptothorax hirticornis)
  • cricket ants (Myrmecophilus manni)
  • spiders (Araneae)
  • eastern kingbirds (Tyrannus tyrannus)
  • western kingbirds (Tyrannus verticalis)
  • flickers (Colaptes auratus borealis)
  • American crows (Corvus brachyrhynchos)
  • Canadian toads (Anaxyrus hemiophrys)
  • Woodhouse's toad (Bufo woodhousei)
  • bears (Ursidae)

Ecosys­tem Roles

Formica ob­scuripes is a mu­tu­al­ist with many species. Hon­ey­dew plays a sig­nif­i­cant role in this species' diet. In ex­change for col­lect­ing and eat­ing hon­ey­dew from the in­sects that it tends, it pro­tects the in­sects from other preda­tors and par­a­sitoids. It also de­stroys in­sects that have been par­a­sitized be­fore the par­a­sitoid com­pletes de­vel­op­ment. The aphids that it tend in­cludes Pleotri­chopho­rus uten­sis, Uroleu­con es­calan­tii, and Lach­nus al­leghe­nien­sis, as well as mem­bers of the fol­low­ing gen­era Aphis, Macrosi­phum, Pleotri­chopho­rus, and many more. It tends hon­ey­dew pro­duc­ing mem­bracids, as well as some jump­ing plant lice, scale in­sects, mealy­bugs, and gall wasps. Thatch nests of Formica ob­scuripes pro­vide shel­ter to many species of in­sects and other Arthro­pods with­out di­rectly im­pact­ing the ants. One such in­sect is the bee­tle Eu­pho­ri­aspis hir­tipes. All life stages of this bee­tle can be found within the thatch. The exact re­la­tion­ship is un­cer­tain, as the ants do not seem to get any­thing out of the bee­tles pres­ence and do not even seem to no­tice them. The bee­tles can also sur­vive in the thatch with­out the ants. Other Arthro­pods found in the thatch and nest of F. ob­scuripes in­clude pseu­doscor­pi­ans, spring­tails, hemipter­ans, dipter­ans, and other bee­tle species. Lar­vae of these Arthro­pods often use the thatch or cham­bers in the nest for hi­ber­na­tion or de­vel­op­ment and feed on de­cay­ing mat­ter. The ants largely ig­nore them. (Con­way, 1997; Er­ick­son, et al., 2012; Gri­nath, et al., 2012; Hen­der­son and Akre, 1986; Mico, et al., 2000; Risch, et al., 2008; Seib­ert, 1992; Seib­ert, 1993)

Ant crick­ets are one no­table species that live in Formica ob­scuripes nests. Ants are ag­gres­sive to­ward the crick­ets and will at­tack if they re­al­ize the crick­ets are there. How­ever, crick­ets have learned to im­i­tate the way ants use their an­ten­nae to iden­tify other in­di­vid­u­als and trick the ants into al­low­ing the crick­ets to stay. Crick­ets even par­tic­i­pate in trophal­laxis with the ants. The ants do not seem to gain any ben­e­fits from the crick­ets' pres­ence, while the crick­ets get shel­ter, food, and will even at­tempt to eat lar­vae if given ac­cess. Other ant species have also been doc­u­mented liv­ing in the nests of Formica ob­scuripes. Formica dakoten­sis has been found liv­ing peace­fully in the same mounds as Formica ob­scuripes in Yel­low­stone Na­tional Park. Lep­totho­rax hir­ti­cor­nis may eat lar­vae and iso­lated work­ers given the op­por­tu­nity, and Tapinoma ses­sile often steals hon­ey­dew from within the nest, but F. ob­scuripes does not act par­tic­u­larly ag­gres­sive to these other ant species. (Con­way, 1996a; Hen­der­son and Akre, 1986; Mico, et al., 2000; Risch, et al., 2008)

Formica ob­scuripes plays a va­ri­ety of other roles in the ecosys­tem. It is prey to a va­ri­ety of in­sects and bird species. It also feeds on a large num­ber of other in­sect species. Ec­topar­a­sitic mites of genus Uropoda are often found on both work­ers and sex­u­als, often in the joints of the legs. The wasp Elas­mo­soma michaeli is a par­a­sitoid of F. ob­scuripes work­ers. The wasp lays eggs in the ab­domens of worker ants, killing the ants upon hatch­ing. As a sig­nif­i­cant aphid-tend­ing ant species, Formica ob­scuripes can play a role in de­ter­min­ing the den­sity of other arthro­pods and her­bi­vores in their habi­tat. In some habi­tats, such as a coastal dune habi­tat, Formica ob­scuripes is a key­stone species. It re­duces com­pet­ing her­bi­vores on the aphid-in­fested plants, while also in­creas­ing arthro­pod den­sity by cre­at­ing new shel­ters by rolling leaves on which the aphids live. Formica ob­scuripes is also known to col­lect seeds and bring them back to the nest. It eats the ed­i­ble part and stores the rest of the seed in cham­bers of the nest. These cham­bers can often be a good habi­tat for the plant to grow and de­velop, al­low­ing the ant to aid in seed dis­per­sal. (Berg-Binder and Suarez, 2012; Con­way, 1996a; Crutsinger and Sanders, 2005; Shaw, 2007)

• Ecosystem Impact
• disperses seeds
• creates habitat
• keystone species

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Formica ob­scuripes colonies likely eat in­sects and other arthro­pods that can be pests to their habi­tat (par­tic­u­larly for­est de­fo­lia­tors), as well as in­sects that could be pests to hu­mans. (McIver, et al., 1997)

• Positive Impacts
• controls pest population

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

There are no known ad­verse ef­fects of Formica ob­scuripes on hu­mans.

Con­ser­va­tion Sta­tus

Formica ob­scuripes has no spe­cial con­ser­va­tion sta­tus.

• IUCN Red List

  Not Evaluated

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Con­trib­u­tors

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

Ref­er­ences

Beat­tie, A., D. Cul­ver. 1977. Ef­fects of the Mound Nests of the Ant, Formica ob­scuripes, on the Sur­round­ing Veg­e­ta­tion. Amer­i­can Mid­land Nat­u­ral­ist, 97/2: 390-399.

Berg-Binder, M., A. Suarez. 2012. Test­ing the di­rected dis­per­sal hy­poth­e­sis: are na­tive ant mounds (Formica sp.) fa­vor­able mi­cro­hab­i­tats for an in­va­sive plant?. Oe­colo­gia, 169/2: 763-772.

Bil­lick, I., C. Carter. 2007. Test­ing the im­por­tance of the dis­tri­b­u­tion of worker sizes to colony per­for­mance in the ant species Formica ob­scuripes Forel. In­sectes So­ci­aux, 54/2: 113-117.

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

Con­way, J. 1996. A field study of the nest­ing ecol­ogy of the thatch­ing ant, Formica ob­scuripes Forel, at high al­ti­tude in Col­orado. Great Basin Nat­u­ral­ist, 56/4: 326-332.

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