Solenopsis molesta

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Solenopsis molesta
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Solenopsidini
Genus: Solenopsis
Species complex: molesta
Species: S. molesta
Binomial name
Solenopsis molesta
(Say, 1836)

Solenopsis molesta casent0005805 profile 1.jpg

Solenopsis molesta casent0005805 dorsal 1.jpg

Specimen labels

Synonyms

This is a common, widely distributed species. Nests are found in the soil (often under stones) and often adjacent to the nests of other species, where it steals food or brood from its host. Specimens have been collected from subterranean, surface and vegetation Vienna sausage bait traps, as well as surface, subterranean and vegetation fire ant bait traps. It is commonly collected in pitfall traps. Reproductives and brood are present throughout the summer. This is also a household pest, although it may not be noticed due to its small size. It hollows out seeds, thus destroying seed in beds. Colonies contain up to a few thousand workers. Sexuals are found in nests from July to October. Nuptial flights occur from late July to early fall, individuals mate in the air. These ants are predaceous, but are also omnivorous (feeding on seeds) and eat dead insects. They also tend Homoptera. (Mackay and Mackay 2002, Pacheco and Mackay 2013)

At a Glance • Facultatively polygynous  
 

Identification

A New World thief ant that is a member of the molesta species complex. (Key to New World Solenopsis Species Complexes)

Pacheco and Mackay (2013) – Worker - This is a small, yellow species (occasionally pale brown), in which the dorsum of the head is finely punctated. The lateral clypeal teeth are well developed while the extralateral teeth are developed into small bumps. The minor funicular segments are typically about 0.14 mm in length. Queen - The queen is moderately large at just over 5.00 mm in total length and concolorous yellow to pale brown. The head and dorsum of the mesosoma are semi-coarsely punctate, with long yellow erect hairs projecting from them. The petiole and postpetiole are horizontally striated. The petiolar peduncle has a small flange ventrally. Male - The male is concolorous dark brown to bicolored with a brown head and gaster and yellow to golden brown body and is moderately large at just under 4 mm in total length. The anterior clypeal margin is convex. The frontal lobes are horizontally striated. The propodeum, petiole and postpetiole are horizontally striated. The petiolar peduncle has an angle ventrally (not a tooth or flange).

As most thief ant species are minute and concolorous yellow in color, it is difficult to differentiate S. molesta from other small species. It is often the case that any small, yellow species is incorrectly named S. molesta. However, Solenopsis molesta is the most common and widespread thief ant in the continental United States. When one collects a small, yellow Solenopsis, there is a high probability it is S. molesta.

This common species can be separated from Solenopsis texana, Solenopsis carolinensis and Solenopsis abdita, by the longer length of the minor funicular segments. It can be separated from Solenopsis krockowi and its relatives, as the punctures on the head are much finer and the minor funicular segments are rarely greater than 0.150 mm in total length. It is difficult to separate the worker of Solenopsis validiuscula. Solenopsis molesta workers are often smaller than those of S. validiuscula (total length 1.80-2.00 mm). The cephalic punctures of S. validiuscula are moderately coarse, while S. molesta are finer. If queens are available, the queens of S. validiuscula are always dark brown, while S. molesta is typically concolorous yellow. The male of S. molesta is light brown and occasionally bicolored, while the male of S. validiuscula is concolorous dark brown. The pedicel of the male of S. molesta is large compared to that of the S. validiuscula male (length nearly as long as the scape). Although the two species are similar in size and form, based on the above differences in the castes, they will be recognized as different species.

It is difficult to separate the workers of S. molesta from S. texana. Solenopsis texana is consistently smaller, with the total length ranging from 1.20-1.30 mm. The queens of S. molesta are easily separated as they are much larger than those of S. texana (total length of S. molesta ranging from 4 - 5.5 mm, the queen of S. texana has a total length of slightly over 3 mm). The queen of S. molesta is yellow or pale brown; that of S. texana is black to dark brown.

The worker is easily confused with those of Solenopsis salina, as both species are yellow and have similar cephalic punctures. They can be separated as the minor segments of the funiculus of S. molesta are nearly always over 0.120 mm in length, those of S. salina are nearly always shorter than 0.100 mm in length. The clypeal teeth of S. molesta are nearly straight, whereas they are usually slightly incurved in S. salina.

Keys including this Species

Distribution

A wide range that includes southern areas of Canada, most of the continental US and northern Mexico.

Distribution based on Regional Taxon Lists

Nearctic Region: Canada, United States (type locality).
Neotropical Region: Mexico.
Solenopsis molesta Distribution.png

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Biology

Solenopsis molesta. Image by Alex Wild.

Solenopsis molesta nests underground, often under stones, generally near the nests of other species where it steals from its host. Solenopsis molesta has been collected in nests of the following species, Myrmica americana, Manica invidia, Pogonomyrmex occidentalis, Pogonomyrmex montanus, Veromessor lobognathus, Monomorium minimum, Pheidole bicarinata, Pheidole pilifera, Dorymyrmex insanus, Camponotus vicinus, Lasius crypticus, Lasius neoniger, Lasius sitiens, Lasius umbratus, Lasius claviger, Lasius interjectus, Lasius murphyi, Formica argentea, Formica neogagates, Formica limata, Formica rubicunda, Formica bradleyi, Formica altipetens and Formica fusca. Colonies contain up to a few thousand workers. Reproductives and brood are present throughout summer to fall. It is occasionally polygynous, with up to eight queens in a single nest. Nuptial flights occur from late July to early fall. (Mackay and Mackay 2002, Pacheco and Mackay 2013)

Hayes provided an extensive accounting of this species in a 1920 publication. His studies were motivated by this ant being a troublesome pest species. The following is selected text from this work:

Foraging/Diet

Seeds as Food The ravages of this versatile little ant on the planted seed of sorghums are much the same as in the damaged fields of corn. Forbes (1894, p. 10) describes the injury to corn as follows:

In the corn field these ants were usually collected about the kernels in the earth, and frequently more or less hidden in little cavities excavated in the softened grain. May 19, 1887, they were very abundant in a field of corn in sod in Champaign county, eating out the planted kernels. In autumn the same species has been detected by us indulging a similar appetite but in a way to do no harm. September 11 to 21, 1893, it was found feeding on and within the kernels of corn at the tips of ears, which had evidently been injured previously by crickets and grasshoppers. The solid substance of the grains is not actually eaten by these ants-a fact which I demonstrated by dissection of the ants-but it is simply gnawed away, doubtless for the sake of the sweetish and oily fluids of the softened kernels. If plants start from seed thus injured, they are shorter than others adjacent, and have a stunted, weak appearance.

Wheeler (1910, p. 268) states that Solenopsis geminata is the only species of the tribe Solenopsidii that is granivorous. However, on a following page (p. 427). quoting Forbes, he mentions X. molesta as eating the kernels of maize and again (p. 269) he states that Solenopsis rufa stores seed in its nest. Say (loc. cit.) first reported the species as an enemy of garden seed. The writer has found the species feeding on planted seed of the following sorghums: Kafir, cane, milo, and feterita. Workers often gather in the fall under corn piled on the ground where they gnaw on broken kernels.

Colony Attributes

Demography

Hayes (1920) Table 1.

Date #w #pupae #semi-pup #larvae #eggs #queens #inqilines
April 16 149 31 20
April 16 481 28 7
April 19 1349 1902
May 1 64 6 216
May 10 535 324 456 662 1182 1
May 29 a a a a a 9
July 20 (b) 216 34 74 12
July 28 (c) 336 247 78 1 1
Aug 10 348 10 1
Sept 2 1436 2012 355 64 28
Sept 3 197 62
Sept 29 312 485 48

(a) not counted (b) one winged queen found (c) four winged queens; two winged males and seventy-three larvae and pupae of sexual forms found

Development

Egg Incubation The length of the period was found to vary from 16 to 28 days, depending on temperature and moisture conditions. Daily egg-laying records of eight queens were kept for a period of 16 days by removing from the nest eggs laid during each day. The average number of eggs laid for the period was 103.3. The greatest number from one individual was 387 and the smallest was 27. One queen deposited 105 eggs in a single day.

Hayes 1920. Figure 7.

Larval Stage The length of the larval stage is highly variable, depending on weather conditions to a marked degree. During midsummer, larvæ were reared to the semipupal stage in 21 days. In another instance, a single larva was under observation from October 10 to May 12 when it transformed to the semipupal stage.

Larval Feeding Larvae are fed regurgitated food by the workers. Workers, in artificial nests, were often seen to place small bits of crushed kafir seeds and torn parts of their larvae and pupae on the bodies of the young near the mouthparts where the larvae were seen to bite them. Larvae were frequently observed, while lying on their back, to straighten out their curved body. These movements are repeated at short intervals and the mandibles open at each up movement and close on the down-movement. These moving larvae were generally fed at once, or soon after making these apparent supplications.

Semipupa

As the larva becomes full grown, a large undigested meconium is voided from the alimentary tract. Workers were seen at times aiding the larva to get rid of this mass by tugging at it while it was being cast off. This change marks the end of larval development and the beginning of the semipupal stage. Large larvæ have often been encountered in nests of this species, which were, undoubtedly, either larvae of males or queens. None were ever reared to maturity in artificial nests. Except for their
Hayes 1920. Figure 8.
much greater size, they resemble the worker larvae, and upon reaching their final stages of growth undergo similar changes to the semipupal stage. In this stage, they are not greatly unlike the larvæ except for the absence of the black mass in the abdomen. The semipupal stage was found in midsummer to vary from 2 to 11 days.

Worker Pupae The comparative size of the worker, the queen and the male pupae is shown in figure 8. When this stage is reached in their development, the sex of the individuals can easily be distinguished by their size.

The worker pupae (fig. 9) are about 1.5 to 1.8 mm. long. When freshly transformed from the larval stage, they are pearly white in color, but as development proceeds, they darken through a creamy white to a pale yellow, and later to a darker yellow which is much the same as the color of the adult worker. The length of the worker pupal stage was found to be from 13 to 27 days. The same period for the males and queens has not been determined.

Queen Pupa The female pupae are larger than the worker pups, measuring about 4.5 mm. long. They are also considerably larger than the pupae of the males. At first, the queens are pearly white, but as development proceeds, they color much the same as the workers. When ready to transform to adults, the queens molt, being greatly assisted in the process by the workers of the colony.

Male Pupae

The pupae of the males are intermediate in size between the worker and queen pupae, being 3.5 to 3.6 mm. long. From a whitish color similar to that of the other pupae, this sex develops to a much darker color, being nearly black. By their size and this black color, they are easily distinguished from the others. Some time previous to their last transformation, the males, as well as the females, develop rather prominent wingpads. Pupae of the males and queens are not found in the colonies until
Hayes 1920. Figure 9. Worker Pupae.
early in July. They frequently occur in fairly large numbers and are well cared for by the workers.

Callow Stage The newly hatched ant, before it has attained its full adult coloration, is called a callow. Except for this lack of color, the callow is almost the same in appearance as the adult workers. At first it is helpless and clumsy and must be cared for by attendant workers, which often carry it about when the need for transportation arises. Callows are even fed by the workers. As they become older and stronger they gradually darken to the adult color and are more and more neglected by the workers until at last they become entirely independent. The coloration, which is due to the deposition of chitin and perhaps some pigment, will take place in two days; that is, in less than two days one cannot distinguish the younger from the older individuals.

Development Time The minimum length of the egg stage was found by the method just described to be 16 days; the larval stage 21 days; the semipupal stage 2 days; and the pupal stage 13 days. Assuming the total of these figures as a probable minimum time required for development of workers, we have 52 days as the least time in which they will mature. The maximum time for development, due to the fact that larvae, will live over the winter, is subject to much variation. The longest time for eggs to hatch was found to be 28 days. As mentioned above, larvae will develop in 21 days. This is in midsummer. Others will live through the winter. A single larva was under observation from October 10 to May 12, when it transformed to the pupal stage. The maximum length of the semipupal stage was found to be 11 days, and that of the pupal period proper was 27 days.

Nesting Biology

Adjustment to certain limited habits seems not to be the rule with the species concerned, at least, not in the localities of Kansas where the ant has been studied. Their wide and varied distribution in such diverse habitats as houses, pastures, meadows, prairies, or plowed fields seems to indicate no especially desired abode. The nature of the soil seems not to be of extreme importance, as colonies are found in heavy clay soils, light sandy soils, or many intermediate gradient types. The colonies are found in almost all situations of this region.

Solenopsis molesta. Image by Alex Wild.

The nest consists of random burrows through the soil, scarcely more than 1 millimeter in diameter, which frequently enlarge to form chambers from 10 to 15 millimeters in diameter. In these large chambers, the brood is reared. Often the one or more openings of a colony under a stone will be greatly enlarged a t the surface of the soil to form brood chambers where the young can be taken, when the soil becomes saturated from rains, to receive the warmth of the sun through the protecting stone. The following field note describing a colony may be regarded as a typical example of a colony:

A large colony of ants was taken under a stone 18 by 12 by 6 inches in a pasture near the State School, Winfield, Kan. At the opening of the nest, there were two entrances; one was nearly round and the other was oblong oval. Several hundred workers were gathered near a large pile of larvae grouped in the round entrance. About 200 workers were on the under surface of the stone when it was turned over. One-half inch below the round entrance about 100 larvae were taken. Tunnels could not be traced from here, but at a depth of 1 1/8 inches a tunnel was found that went south for 4 inches at the end of which were about 3000 larvae. These larvae were in a chamber about one-half of an inch in diameter. Directly below this room at a depth of 2 ½ inches from the surface, a tunnel went north for 3 inches and ended in a chamber containing about 200 larvae. Down 3 inches, a tunnel was followed in an easterly direction of 1 ½ inches where it divided, one branch going directly east while the other went downward and in the same easterly direction for 2 inches. At the end of each were large chambers containing piles of larvae. Workers and larvae were scattered throughout the tunnels. No evidence of food being stored was found. No queen was found.

This colony was taken in early spring and contained no eggs or puae. Otherwise, the colonies examined later in the season do not differ much in their general aspects.

Associations with other Organisms

Other Ants

Hayes 1920. Figure 1. Worker

It is not impossible, as supposed in the case of Solenopsis fugax, that isolated nests of S. molesta may be connected with nests of other ants by long underground galleries. It is perhaps by this hypogæic mode of travel that the workers are able to find and devastate fields of planted sorghum seed.

This species is often found under stones with colonies of other ants. The two colonies are connected by small galleries forming what are called compound nests. These small tunnels ramify through the workings of the larger ants. The minuteness of the galleries prevents the larger species from molesting the small invaders who, with comparative safety, forage at will.

Wheeler (1901, p. 533) reports S. molesta living in lestobiotic relationship with the following ants: Pachycondyla harpax Fabr., Odontomachus clarue Roger, Camponotus sansabeanus,Camponotus festinatus, Formica, Lasius, Stenamma, and Myrmica. Forbes (1908, pp. 38, 41-42.) records it living in harmony with Lasius niger-americanus Emery, and King (1896, p. 169) with L. niger Linn. Other ants with which it has been found are: Ponera pennsylvanica (King 1896, p. 169), Camponotus americanus Mayr (King, 1895, p. 221), Lasius interjectus Neyr. (King 1895, p. 222), L. claviger Rog. (King, 1895, p. 222), Prenolepis parvula Mayr (King, 1896, p. 170), P. imparis Say (Mann, 1911, p. 30), Myrmica lobicornis Myl. (King, 1856, p. 170), Tapinoma sessile Say (Mann, 1911, p. 30), Pheidole californica Mayr (Mann, 1911, p. 30), Camponotus maccooki Forel (Mann, 1911, p. 30), C. maculatus vicinus Mayr (Mann, 1911, p. 30), Formica fusca Linn. (King, 1896, p. 169), F. fusca var. subsericea Say (King, 1896, p. 169), Aphaenogaster fulva Rog. (King, 1896, p. 170), Formica pallisle-fulva subsp. nitidiventris Em. (King, 1896, p. 169), F. cinerea Mayr (Wheeler, 1902, p. 952) and the termite, Termes flavipes (King, 1895, p. 220). In this investigation, S. molesta was taken in colonies of Iridomyrmex pruinosus var. analis Ern. Andre, Cremastogaster lineolata var. punctullata Emery, Hypoponera inexorata, Pheidole sp., and the termite, Leucoterms lucifugus Rossi.

Other Insects

Among those that live in the nests are two myrmecophiles reported by Schwarz (1890, p. 241; 1890, pp. 244 and 247), a species of Lithocharis, and a species of Myrmecochara. Other insects that have been reported found in the nests are Atheta exilissima Casey (Wickham, 1894, p. 80). Rhyssemus sonatus Lec. (Wickham, 1892, p. 322) (possibly accidental), Isobrachium Myrmecophilum Ash. (Mann, 1911 p. 29). Aleocharini g. et sp. (King, 1897, p. 102), and Auxopaedeutes sodalis Brues (Brues, 1903, p. 127). Dactylopius sp., a mealy bug, was found repeatedly in the nests of S. molesta in Kansas, this being the only true inquiline observed. When so found, there are generally a number of grass roots in the soil near the nests where the mealy bugs can get their nourishment. Workers will pick up these guests as they do with their own young and carry them to places of safety when danger threatens, Other types of associates are those upon which the ants are in attendance, such as aphids and scale insects; while still another group includes those upon which the ant preys.

Hayes 1920. Figure 4. Queen.

This ant has varied habits. As a beneficial predaceous insect it receives perhaps as much prominence as it does as a pest. The beneficial aspect is manifested by the activities of the ant in attacking many of our other pernicious pests. A glance at the accompanying list of species which S. molesta attacks will serve to show the ant's usefulness. The names in the list without references are from original observations.

Insect species known to be attacked by S. molesta are as follows:

Grape curculio, Craponius inæqualis (Brooks, 1906, p. 241)

Walnut curculio, Conotrachelus juglandis (Brooks, 1910, p. 182).

Cotton boll weevil, Anthonornus grandis (Pierce, 1912, p. 41).

Chinch bug (eggs), Blissus leucopterus (Headlee and MeColloch, 1913,

Codling moth, Carpocapsa pomenella (Brooks and Blakeslee, 1915,

Maize billbug, Sphenophorus maidis.

Corn stalk borer, Papaipema nitella.

Corn earworm, Chloridea obsoleta.

Hessian fly, Mayetiola destructor.

Grasshopper (eggs), Acrididæ (different species).

Ladybird beetle, Megilla maculata.

White-marked tussock moth, Hemerocampa leucostigma.

Scarabæidæ, Ligyrus relictus.

Larger ants:

Other colonies of S. molesta.

The amount of damage which this species inflicts on crops and its noxious character in kitchens is somewhat compensated for by predaceous habits. Unfortunately, the ant does not appear to be of material value as an enemy of any of the species mentioned in the list for in most, if not all, cases the report of molesta as an enemy of various insects comes from isolated and, perhaps, chance observations. In the opinion of the writer, many of these cases arise when the ants find an injured or helpless victim that is incapable of defense, or it is even possible that they attack their victim after it has died. These reasons, combined with records of the ant feeding on fats, grease, and cured hams, might lead to the conclusion that many of the accounts of molesta as a predaceous enemy are only instances of the ant's scavenger habits.

Enemies The known enemies of S. molesta are few and of widely different kinds. Spiders often trap the workers in their webs. Two other ants, Crematogaster lineolata and soldier ants of Pheidole pilifera, were observed killing workers. The common horned toads (Phrymoma cornutum Harlan), upon examination of their stomach contents, were found to have eaten numbers of S. molesta workers. In the stomach of a skunk (Eumeces sp.), one S. molesta worker was found. A small mite (Hypaspis sp.), which is probably ectoparasitic, was repeatedly taken on workers, queens, and eggs. West (1910, pp. 14-22) found S. debilis in the stomachs of two moles. No endoparasites are known.

The following birds are known enemies of S. molesta: English sparrows, bank swallows, barn swallows, chipping sparrows (Judd, 1902, pp. 33-34), flicker (Beal, 1911, p. 56) and the kingbird (Beal, p. 16, and Judd, loc. cit.).

Humans

Agriculture When first reported, Say (1836, pp. 293-294) stated that the species attacked garden seed, whether the seed was planted of not he fails to mention. The next reference, by Fitch (1856, pp. 129-130), reports the ant so numerous in the fields as to threaten to cut off every blade of corn by gnawing the tender leaves “for the purpose of drinking the sweet juice which flows from the wounds.” Forbes (1884, p. 45) found this insect, which he called Solenopsis fugax, in great numbers in sorghum and broom-corn fields, where he noted they were paying no attention to the superabundant plant lice. They were also observed (Forbes, 1884, pp. 61; 112-113) gnawing out the fleshy fruit of strawberries and hollowing out planted seed corn. As Solenopsis debilis Forbes later (1894, pp. 8-10; 66; 69) noted further injury to corn, both in the ground and in ears of standing corn which had been previously injured by crickets and grasshoppers. Workers were several times noted in attendance on the corn root-louse, Aphis maidi-radicis Forbes, and a minor aphid of the corn plant, Geoica squamosa Hart. Hunt (1886, p. 58) lists both S. fugax and S. molesta as enemies of corn.

Hayes 1920. Figure 5. Male.

Webster (1890, pp. 257-258) observed this ant attending a species of Dactylopius on red clover. Workers were seen carrying away the substance of seed corn after it had been planted. He also described them (1893, p. 158) as injuring blackberries, concerning which he says “their attacks upon ripe fruit is exceedingly annoying, as their diminutive size prevents their being readily discovered.” Felt (1915, pp. 68-69) found the species injuring corn a t Salt Point, N. Y. In this instance, recently planted corn seemed to be “growing smaller” and it was found that the ant was eating the interior out of the kernels as described by Forbes. The development of the plants was arrested and they appeared to become smaller.

As a field pest in Kansas, the chief damage consists largely of the destruction of seeds of kafir, cane, milo, feterita, and corn (maize) soon after they are planted. Injury to the sorghums is much the same as that described by other workers in the case of corn, concerning which Forbes (1894, p. 9) writes, “a kernel may be found wholly or partly hollowed out, the mealy interior being not devoured, but scattered about in the earth, while the cuticle or outer shell of the seed remains but little disturbed.”

During the past few years, thousands of acres of sorghum crops have had to be replanted from one to six times because of the ravages of this ant and in a number of cases it has been impossible to get a good stand. With seed at $3 per bushel, as it was during the season of 1914, this means a considerable monetary loss as well as time and labor spent in replanting. A few of the following records from field notes and correspondence will serve to show more vividly the amount of damage done by this pest.

May 7, ’12, Milton Clegg, Neodesha, reported that ants destroyed 40 acres of cane and kafir.

May 12, ’13, A. T. Sharp, Council Grove, reported ants injuring listed kafir.

June 18, ’13, E. W. Dales, Eureka, had 100 acres in cane and kafir, but because of the ants only 25% germinated.

Feb. 10, ’13, Chas. C. Crane, Longton, writes that on account of the ants most of the farmers in his neighborhood were compelled to replant several times last year, and some did not, even then, get a stand.

June 27, ’12, B. P. Cunningham, Augusta, stated that farmers replanted five times in ant infested fields in his vicinity.

April 23, ’14, W. Russell, Winfield, replanted 80 acres infested with ants three times last year and was finally left with about a twenty acre stand.

Feb. — ’15, Frank Lister, Olpe, says he had 20 acres of kafir destroyed by ants last year.

Jan. — ’16, Henry Hanson, Rosalia, states that the ant is very bad. Last year he replanted seven times without obtaining a stand.

House Pest This phase of the insect’s depredations has not attracted much attention in Kansas. Several reports of yellow ants as pests in houses in this state have, upon investigation, proved to be the larger ant, Monomorium pharaonic. There are but two records in the files of the Experiment Station of S. molesta as a household pest. One is from Kansas City, Mo., and the other a record of the ant being abundant in a clothes closet in Manhattan.

However, there are numerous accounts of the species infesting houses in other localities. Say (loc. cit.) records the ants as being found in houses in great numbers where they eat vegetable food, olive oil, and grease. Fitch (1856, p. 129) calls it the most abundant and annoying ant in the State of New York, where it is common in dwellings, being attracted by sweet-meats, preserves and other sweetish substances. As a pest of insect collections, he says: “I have experienced some difficulty in preserving my collection of insects from this depredator, some box or drawer not perfectly tight being invaded by them ere I am aware of it, almost every season. But by crushing every individual which does not escape into some crevice, and permitting their dead bodies to remain where they are slain, their comrades take warning and cease to frequent the spot. The vapor of camphor also repels them.” Packard (1880, p. 185) states that Myrmica molesta is found in houses all over the world. Evidently, he confused the species with other house ants, for S. molesta is a native North American ant and is not so widely distributed as Packard would lead us to believe. Webster (1890, pp. 257-258) found the ants burrowing into cured hams and ripe apples. Later (1893, p. 158) he states: “Several times this insect has made itself exceedingly disagreeable in my own house, by its presence in the pantry, and while in Washington some years since, the artist of the Division of Pomology, Department of Agriculture, complained to me of the trouble he experienced from a closely allied species, Solenopsis debilis, Mayr, eating the paints with which he was coloring the wax models of fruit.” Wheeler in different articles (1905, pp. 377-378; 1910, p. 427) mentions the species as a pest of houses and disproves Forel’s (1901, pp. 344-345) assertion that S. molesta does not occur in houses. Barber (1912, p. 181), in a paper on the avocado weevil, discussing seeds of the avocado infested with weevil, says: “Unfortunately the seed lay for a time on his desk subject to the attack, of the ant pest (Solenopsis debilis) from which the Bureau of Entomology suffers. . . .” Tanquary (1912, p. 138) reports that the ant is sometimes found in houses. Herrick (1914, p. 178) states “The tiny thief-ant (Solenopsis molesta) is a native ant that occasionally leaves its natural haunts and builds its nest in houses, where the occupants become pests in kitchens and pantries.”

Castes

Worker

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • molesta. Myrmica molesta Say, 1836: 293 (q.) U.S.A. Wheeler, G.C. & Wheeler, J. 1955c: 134 (l.); Petralia & Vinson, 1980: 383 (l.); Crozier, 1970: 116 (k.). Combination in Solenopsis: Mayr, 1863: 407; in S. (Diplorhoptrum): Creighton, 1950a: 237. Senior synonym of debilis, exigua, minuta: Emery, 1895c: 277; Emery, 1896g: 85.
  • minuta. Myrmica minuta Say, 1836: 294 (w.) U.S.A. Junior synonym of molesta: Emery, 1895c: 277.
  • exigua. Myrmica (Tetramorium) exigua Buckley, 1867: 342 (w.q.) U.S.A. Junior synonym of molesta: Emery, 1895c: 277. See also: Wheeler, W.M. 1902f: 28.
  • debilis. Solenopsis debilis Mayr, 1886d: 461 (w.q.m.) U.S.A. Junior synonym of molesta: Emery, 1895c: 277; Emery, 1896g: 85.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

Worker

Pacheco and Mackay (2013) - Measurements (n=6). TL 1.38-1.62 (1.50); HL 0.420-0.510 (0.457); HW 0.360-0.432 (0.386); EL 0.036-0.042 (0.040); ED 0.030-0.036 (0.032); SL 0.282-0.348 (0.317); FSL 0.132-0.156 (0.141); CI 81.1-87.8 (84.5); SI 64.7-72.9 (69.4); PL 0.072-0.096 (0.083); PW 0.120-0.156 (0.126); PI 57.7-80.0 (66.3); PPL 0.102-0.120 (0.108); PPW 0.120-0.162 (0.135); PPI 74.1-85.7 (80.4); WL 0.300-0.342 (0.325); PSL 0.030-0.036 (0.032); PSW 0.030.

Small; concolorous yellow to pale brown; head longer than wide, sides nearly straight, finely punctate; lateral clypeal teeth well developed, extralateral teeth absent; clypeal carinae well defined; scape long, nearly reaching posterior lateral corner of head; minor funicular segments moderately long; eye small, 3-5 ommatidia; pronotum finely punctate, smooth and shiny between punctures; mesopleuron smooth and shiny; notopropodeal suture well depressed, notch-shaped, groove breaks sculpture of mesosoma; posterior border of propodeum rounded; propodeal spiracle small, round; metapleuron horizontally striated; petiole wider than postpetiole viewed laterally; petiolar peduncle with minute angle ventrally; postpetiolar node semicircular viewed laterally, lacking tooth or flange ventrally.

Abundantly hairy, pilosity yellow; erect and suberect hairs covering all body surfaces; scape with numerous appressed hairs; dorsum of mesosoma with hairs of various lengths (0.060-0.120 mm); hairs on petiole, postpetiole and gaster curve posteriorly.

Queen

Pacheco and Mackay (2013) - Measurements (n=6). TL 4.68-5.64 (5.36); HL 0.720-0.840 (0.781); HW 0.642-0.780 (0.743); EL 0.240; ED 0.180; MOL 0.072-0.120 (0.103); MOD 0.072-0.120 (0.097); SL 0.516-0.540 (0.536); FSL 0.300; CI 89.2-98.5 (95.1); SI 64.3-71.7 (68.7); PSL 0.072-0.078 (0.075); PSW 0.060; PL 0.120; PW 0.276-0.384 (0.350); PI 31.3-43.5 (34.7); PPL 0.276-0.360 (0.306); PPW 0.330-0.420 (0.405); PPI 71.4-85.7 (75.8); WL 0.960-1.20 (1.12).

Moderately large; concolorous yellow to pale brown; head longer than wide, posterior border slightly concave, semi-coarsely punctate; lateral clypeal teeth well developed, extralateral teeth absent; clypeal carinae well defined; frontal lobes vertically striated; eyes large, extend 0.084 mm past lateral margin of head; scapes long, reach lateral ocelli; medial ocellus small, depigmented; dorsum of mesosoma semi-coarsely punctate, smooth and shiny between punctures; posterior propodeal margin viewed laterally slightly angled; propodeal spiracle small, oval; metapleuron horizontally striated; sides of petiolar and postpetiolar nodes horizontally striated; petiolar peduncle with thin flange ventrally; postpetiole lacking tooth or flange ventrally.

Abundantly hairy, pilosity yellow; numerous erect and suberect hairs of various lengths on all body surfaces; hairs on dorsum of mesosoma long (0.120-0.180 mm); hairs on petiole and postpetiole long (up to 0.240 mm), curve posteriorly.

Male

Pacheco and Mackay (2013) - Measurements (n=6). TL 3.48-4.32 (3.85); HL 0.498-0.516 (0.504); HW 0.510-0.534 (0.518); EL 0.276-0.300 (0.282); ED 0.216-0.228 (0.225); MOL 0.078-0.108 (0.091); MOD 0.102-0.120 (0.111); SL 0.204-0.228 (0.212); FSL 0.960-1.02 (0.972); CI 102-104 (103); SI 40.7-44.7 (42.3); PSL 0.078-0.090 (0.083); PSW 0.060; PL 0.132-0.144 (0.138); PW 0.252-0.282 (0.266); PI 48.9-55.8 (52.1); PPL 0.240; PPW 0.300-0.360 (0.324); PPI 66.7-80.0 (74.4); WL 0.960-1.08 (1.05).

Moderately large; concolorous dark brown to bicolored (darker head and gaster than mesosoma); head smooth and shiny with scattered fine punctures, wider than long; anterior clypeal margin convex, lacking teeth or carinae; frontal lobes vertically striated, extend laterally then anteriorly to clypeal margin; antennae long, yellow; eyes large, extend 0.120 mm past lateral margin of head; medial ocellus large, lacking pigment; semi-coarse punctures on pronotum, smooth and shiny between punctures; posterior propodeal margin viewed laterally rounded; propodeal spiracle small, round; propodeum striated; petiolar node rounded dorsally, horizontally striated, peduncle lacking tooth or flange ventrally, but with angle; postpetiolar node flattened dorsally, horizontally striated, lacking tooth or flange ventrally.

Abundantly hairy, pilosity yellow; erect and suberect hairs of various lengths covering all body surfaces; most hairs on pronotum about 0.120 mm in total length; hairs on petiole and postpetiole curve posteriorly.

Type Material

Pacheco and Mackay (2013) - None known to exist (type locality, Indiana). Apparently, none of the type series exist today. We picked the most common specimens that range near the type locality to anchor the identity of this species. Additionally, we knew the identity of closely related species.

References

  • Creighton, W. S. 1950a. The ants of North America. Bull. Mus. Comp. Zool. 104: 1-585 (page 237, Combination in S. (Diplorhoptrum))
  • Crozier, R. H. 1970a. Karyotypes of twenty-one ant species (Hymenoptera: Formicidae), with reviews of the known ant karyotypes. Can. J. Genet. Cytol. 12: 109-128 (page 116, karyotype described)
  • Emery, C. 1895d. Beiträge zur Kenntniss der nordamerikanischen Ameisenfauna. (Schluss). Zool. Jahrb. Abt. Syst. Geogr. Biol. Tiere 8: 257-360 (page 277, Senior synonym of debilis, exigua and minuta)
  • Emery, C. 1896g. Studi sulle formiche della fauna neotropica. XVII-XXV. Bull. Soc. Entomol. Ital. 28: 33-107 (page 85, Senior synonym of debilis, exigua and minuta)
  • Hayes, W. P. 1920. Solenopsis molesta Say (Hym.): a biological study. Kansas State Agricultural College, Agricultural Experiment Station. Manhattan, KS. Technical bulletin No. 7. 55 p.
  • Mackay, W. P. and E. Mackay. 2002. The ants of New Mexico (Hymenoptera: Formicidae). Edwin Mellen Press, Lewiston, NY.
  • Mayr, G. 1863a. Formicidarum index synonymicus. Verh. K-K. Zool.-Bot. Ges. Wien 13: 385-460 (page 407, Combination in Solenoopsis)
  • Pacheco, J.A. & Mackay, W.P. 2013. The systematics and biology of the New World thief ants of the genus Solenopsis (Hymenoptera: Formicidae). Edwin Mellen Press, Lewiston, New York. 501 pp.
  • Petralia, R. S.; Vinson, S. B. 1980 [1979]. Comparative anatomy of the ventral region of ant larvae, and its relation to feeding behavior. Psyche (Camb.) 86: 375-394 (page 383, larva described)
  • Say, T. 1836. Descriptions of new species of North American Hymenoptera, and observations on some already described. Boston J. Nat. Hist. 1: 209-305 (page 293, queen described)
  • Wheeler, G. C.; Wheeler, J. 1955c. The ant larvae of the myrmicine tribe Solenopsidini. Am. Midl. Nat. 54: 119-141 (page 134, larva described)