Trichomyrmex destructor

A widespread invasive species originally described from India and occurring in tropical and subtropical regions of the world (Wetterer 2009b), supposedly spread from central Asia west to north Africa (Forel 1909; Sharaf 2006), southern Europe (Ruzsky 1907) and the Arabian Peninsula (Collingwood 1985; Collingwood and Agosti 1996). In the USA it is reported from Key West and Tampa (Deyrup et al. 2000).

Identification
Polymorphic workers.

Trichomyrmex destructor is very similar to the closely related Trichomyrmex robustior, but is lighter in color and the eyes tend to be less elongate. Workers within nests also show more allometric variation than is found in T. robustior (Heterick 2006).

From Bolton (1987) Worker. TL 1-8-3-5, HL 0-50-0-88, HW 0-40-0-79, CI 76-92, SL 0-41-0-56, SI 70-104, PW 0-23-0-45, AL 0-54-0-92 (55 measured).

Workers showing marked size variation in any given series, and displaying monophasic allometric variation. Mandibles with 3 strong teeth, the fourth (basal) reduced to a minute offset denticle. Mandibles usually with distinct longitudinal rugulose or striate sculpture, even in the smallest workers. Only rarely the smallest workers with mandibles virtually smooth. Eyes relatively small, the maximum diameter 0-14-0-20 x HW and with 4-6 ommatidia in the longest row. In general eyes of smaller workers relatively somewhat larger in relation to head width than in larger workers, but not as conspicuously so as in oscaris. In larger workers CI is higher than in smaller workers, the heads becoming relatively broader with increased size.

Antennal scapes relatively longer in small workers and shorter in larger individuals, as follows.

When HW 0-40-0-45 then SI is 104-95;

when HW 0-45-0-55 then SI is 97-85;

when HW 0-55-0-65 then SI is 86-76;

when HW 0-65-0-79 then SI is 78-70.

Note that within the size intervals given the scapes are always relatively longer here than in oscaris (see below). Scapes when laid straight back from their insertions reaching the occipital margin in smallest workers but falling short of the margin in larger individuals. Alitrunk in profile with promesonotum convex and metanotal groove impressed. Petiole node in dorsal view globular to subglobular, not distinctly anteroposteriorly compressed. Occipital margin of head with 2-4 pairs of hairs forming a transverse row.

Dorsum of head in front of this row but behind the frontal lobes with 1-4 pairs of hairs straddling the midline. Pubescence on head sparse and directed towards the midline. Promesonotal dorsum always with numerous elongate standing hairs; such hairs usually present on propodeum but may be lacking in small workers. Petiole, postpetiole and gaster with backward directed elongate hairs.

Cephalic dorsum unsculptured except for scattered hair-pits. A band of fine transverse striolate sculpture present on the rim of the descending occipital surface of the head; this band of weak sculpture usually just visible in full-face view along the rim of the occipital margin. In the smallest workers this sculpture may be very faint or rarely even absent. Propodeal dorsum always finely transversely striolate to rugulose and usually with punctulate sculpture also present, at least in larger workers of any given series. The transverse sculpture is fainter in smaller than in larger workers but the overall intensity of the sculpture may vary between series. Promesonotum usually smooth and shining with scattered hair-pits, but peripheral faint sculpture may occur in large workers. Sides of pronotum smooth to vestigially striolate, the remainder of the sides of the alitrunk punctate to reticulate-punctate; the sculpture more intense and wider distributed in larger than in smaller workers. First gastral tergite smooth except for hair-pits. Head, alitrunk, petiole and postpetiole uniformly glossy yellow, varying in shade from light yellow to dull brownish yellow. Gaster always much darker, dark brown to blackish brown, usually with a conspicuous yellowish area mediobasally, the extent of which is very variable but is sometimes absent, leaving the gaster uniformly dark.

Two closely related species occur in sub-Saharan Africa, oscaris and mayri. The latter matches the description of destructor given above but is uniformly dark brown to blackish brown; see under mayri for further discussion. M. oscaris is uniformly coloured, unlike destructor, and has the petiole and postpetiole shaped differently in larger workers. Apart from this the antennal scapes of destructor are relatively longer than those of oscaris in workers of comparable absolute dimensions, compare the tables given under their respective descriptions.

Distribution
Trichomyrmex destructor has a widespread distribution in tropical and subtropical parts of the Old World, except in sub-Saharan Africa. In the New World, however, it is found only in Florida (where it is rare, being only known from Key West and Tampa (Deyrup, Davis & Cover, 2000)), the West Indies, and the Galapagos Islands (Wetterer 2009).

Distribution based on Regional Taxon Lists
Afrotropical Region: Cape Verde, Comoros, Eritrea, Guinea, Kenya, Mozambique, Saudi Arabia, Socotra Archipelago, South Africa, United Arab Emirates, United Republic of Tanzania, Yemen. Australasian Region: Australia. Indo-Australian Region: Cook Islands, Fiji, Guam, Indonesia, Kiribati, Krakatau Islands, Micronesia (Federated States of), New Guinea, Niue, Northern Mariana Islands, Palau, Philippines, Samoa, Singapore, Solomon Islands. Malagasy Region: Madagascar, Mauritius, Mayotte, Seychelles. Nearctic Region: United States. Neotropical Region: Barbados, Brazil, Colombia, Cuba, Dominican Republic, Ecuador, Galapagos Islands, Greater Antilles, Guadeloupe, Haiti, Puerto Rico, Trinidad and Tobago. Oriental Region: Bangladesh, India, Laos, Nepal, Sri Lanka, Thailand. Palaearctic Region: Afghanistan, Canary Islands, China, Iran, Iraq, Israel, Japan, Kuwait, Oman, United Kingdom of Great Britain and Northern Ireland, Uzbekistan.



Biology
As reported from the Global Invasive Species Database:

Nest outdoors or in buildings, depending largely on whether they occur in tropical, semitropical or temperate regions. In northern Western Australia they do not live far from houses where they live above the ground in wall and roof cavities. They are present in some tropical, irrigated, lowland rice fields in the Philippines, and coconut plantations in Sri Lanka. In Florida they nest in soil (lawns) or buildings. On Tiwi Island and in Australia's Northern Territory, M. destructor nests were only associated with urban areas; while there was some spread into surrounding bush land, they appear to be unable to establish in undisturbed habitat. In the United Arab Emirates the ants are present in a wide range of habitats, especially irrigated gardens and disturbed habitats close to water. In the Caribbean they were found nesting in trees in citrus orchards (in hollow twigs and branches) and on the ground (Collingwood et al. 1997; and Harris et al. 2005).

M. destructor is a tramp ant, renowned for transportation via human commerce and trade. It is associated with a wide range of freight types, making it difficult to target any particular pathways. This ant also spreads naturally from established colonies in two ways: colony budding, where queens walk on foot accompanied by workers to a new nesting site; and winged dispersal of inseminated queens to uninfested areas where they start a new colony. This latter mechanism needs to be confirmed; it is most likely colony budding is the primary natural dispersal method (Harris et al. 2005).

Madagascar
Heterick (2006) - Samples have been taken in tropical dry forest in north and north-western Madagascar in the Antsiranana and Jahajanga Provinces, where they have been collected under stones, from a dead branch and by sweeping. Populations also may be expected to occur generally in severely damaged habitats in these regions.

Yemen
Sharaf et al. (2017) - Trichomyrmex destructor is one of the most successful invasive species on Socotra Island, occupying diverse habitats. It was found nesting directly in soil under a rock. Several workers were found in leaf litter under Eragrostis eragrostis (L.) (Poaceae), where the soil was dry and rich in organic material. Several individuals were nesting under a rock in very moist, compact, clay soil. A nest was found under the bark of a dead rotten log located on a mountainside where a small stream was draining a mountain crest surrounded by diverse plant communities. Another nest series was found in leaf litter under a tree of Ficus cordata Thunb (Moraceae).

Associations with Humans
Wetterer (2009) reported:

"In the past, M. destructor was primarily spread by ship. For example, CLARKE (1922) reported M. destructor was a serious problem on steamers traveling between California and the East Coast US via Panama Canal, writing that M. destructor "not only caused a considerable pecuniary loss in the destruction of food stuffs but attacked passengers and crew… They would find their way in small or large numbers into the beds and their bites were very painful." WEBER (1939) found live M. destructor in his luggage in Massachusetts several days after returning from Cuba by ship. Now, air travel, combined with the ant's propensity of nesting in electrical and electronic equipment, allows the possible spread of M. destructor to virtually anywhere in the world. For example, ENGST (2005) reported that, on arrival in New Zealand, an air passenger found M. destructor living inside a sealed iPod bought in the air-port in Fiji.

I found many reports of M. destructor destroying property and attacking people. For example, STONEY (1995) wrote that in Western Australia, M. destructor "has been known to chomp through a grown man's thong overnight and chew up anything from polystyrene cups to wiring in cars, telephones and houses... The insect has even nibbled on newborn babies sleeping in their cots and left big holes in car tyres. 'Kids are virtually being eaten alive while they sleep at night,' the Derby shire president, Mr. Peter McCumstie, said." CHIN (1998) wrote how in Darwin, Australia, M. destructor "can cause havoc in the household since they bite and may occur almost everywhere inside the house, feeding on a wide variety of food materials. They frequently nest in power sockets and chew on electrical wiring and in some cases have started electrical fires." In the community of Nguiu on Bathurst Island, Australia, B. Hoffmann investigated an enormous outbreak of M. destructor (CSIRO 2003). Hoffmann reported, "The magnitude of damage is really overwhelming… There were massive trails going into houses from all directions – millions and millions of Singapore ants [M. destructor] swarming everywhere. These ants get into power points, they eat electrical wiring and short circuit the power – two houses have already burned down recently because of damage caused to electrical systems (ANONYMOUS 2003). On Tobi Island and Helen Reef Atoll in Palau, BOUDJELAS (2006) reported that M. destructor'' was a serious threat to essential infrastructure and "causes extensive economic damage in human settlements by damaging fabric and rubber goods and removing insulation from electric cables." LEE & al. (2002) found that in surveys of food preparation outlets on Penang Island, Malaysia, M. destructor was the dominant ant species, making up 27.8% of the ant specimens collected.

In the Dry Tortugas, the outermost of the Florida Keys, MAYOR (1922) reported that M. destructor on Loggerhead Key was "a great pest in the wooden buildings of Tortugas Laboratory, making its nests in crevices of the woodwork. So voracious are these insects that we are obliged to swing our beds from the rafters and to paint the ropes with a solution of corrosive sublimate, while all tables must have tape soaked in corrosive sublimate wrapped around their legs if ants are to be excluded from them. These pests have the habit of biting out small pieces of skin, and I have seen them kill within 24 hours rats which were confined in cages." At Tortugas Laboratory, "one of the scientists, a newcomer who allowed his sheet to touch the floor, was stung so badly by a swarm of them that he lapsed into unconsciousness for a while" (STEPHENS & CALDER 2006). The Tortugas Laboratory buildings were later abandoned and torn down. Remarkably, no subsequent collector found M. destructor on Loggerhead Key (WETTERER & O'HARA 2002). Elsewhere in the Florida Keys, DEYRUP (1991) wrote that M. destructor "is spectacularly common on Key West." In a recent visit to Key West, however, I was unable to find any M. destructor. Instead, all areas where I collected on Key West were dominated by P. megacephala and/or S. invicta (J.K. Wetterer, unpubl.).

Monomorium destructor populations appear to be expanding in the West Indies, where they are a serious household problem. For example, in my apartment in Tunapuna, Trinidad, enormous trails of M. destructor foragers streamed out of an electrical socket and into the cupboards, trashcan, and kitchen sink, carrying off any scrap of food they could find. In an electronics store in Aripo, Trinidad, the owners reported this species nesting inside their computers. In a hotel room in Grand Anse, Grenada, a large trail of M. destructor emerged out of the air-conditioner to forage in my trashcan. In addition to urban areas, I also found M. destructor swarming down trees in parks and disturbed forests, for example in beachfront parks on Grenada, St. Croix, St. Vincent, and St. Lucia and in a forest of the poisonous manchineel tree (Hippomane mancinella LINNAEUS, 1753) on Curaçao.

Worker
Workers are polymorphic.

Nomenclature

 *  destructor. Atta destructor Jerdon, 1851: 105 (w.) INDIA. Bingham, 1903: 209 (q.m.). Combination in Monomorium: Dalla Torre, 1893: 66; in M. (Parholcomyrmex): Wheeler, W.M. 1922a: 874; in Trichomyrmex: Ward et al., 2014: 16. Senior synonym of ominosa (and its junior synonym atomaria): Dalla Torre, 1893: 66; of basalis: Forel, 1894b: 86; of vexator: Donisthorpe, 1932c: 468; of gracillima: Bolton, 1987: 324. See also: Smith, D.R. 1979: 1382; Bolton, 1987: 324; Heterick, 2006: 96.
 * basalis. Myrmica basalis Smith, F. 1858b: 125 (w.) SRI LANKA. Combination in Monomorium: Mayr, 1865: 92. Junior synonym of destructor: Forel, 1894b: 86.
 * atomaria. Myrmica atomaria Gerstäcker, 1859: 263 (w.) MOZAMBIQUE. [Also described as new by Gerstäcker, 1862: 518.] Junior synonym of ominosa: Roger, 1863b: 31.
 * ominosa. Myrmica ominosa Gerstäcker, 1859: 263 (w.) MOZAMBIQUE. [Also described as new by Gerstäcker, 1862: 517.] Combination in Monomorium: Roger, 1863b: 31. Senior synonym of atomaria: Roger, 1863b: 31. Junior synonym of destructor: Dalla Torre, 1893: 66.
 * gracillima. Myrmica gracillima Smith, F. 1861a: 34 (w.) ISRAEL. Emery, 1877b: 369 (footnote) (q.m.). Combination in Monomorium: Mayr, 1862: 753; in M. (Parholcomyrmex): Emery, 1915i: 190. Subspecies of destructor: Forel, 1913d: 437. Junior synonym of destructor: Bolton, 1987: 324.
 * vexator. Myrmica vexator Smith, F. 1861b: 47 (w.) INDONESIA (Ternate I.). Junior synonym of destructor: Donisthorpe, 1932c: 468.

Type Material


Myrmica vexator

Three worker syntypes in. Labelled “Ter. 21.” (= Ternate I.)

Worker
Heterick (2006) - HEAD: Head square; vertex planar or weakly concave; frons longitudinally finely striolate anteriad (striolae curving inwards around antennal insertions), smooth and shining posteriad, except for a few transverse rugulae on upper vertex; pilosity of frons consisting mainly of appressed and decumbent setulae with a few erect setae on vertex. Eye large, eye width 1.5× greater than greatest width of antennal scape to moderate, eye width 1–1.5× greatest width of antennal scape; (in full-face view) eyes set below midpoint of head capsule; (viewed in profile) eyes set around midline of head capsule; eye elliptical, curvature of inner eye margin may be more pronounced than that of its outer margin. Antennal segments 12; antennal club three-segmented. Clypeal carinae indicated by multiple weak ridges; anteromedian clypeal margin broadly convex to straight; paraclypeal setae moderately long and fine, curved; posteromedian clypeal margin extending slightly beyond level of posterior margin of antennal fossae. Anterior tentorial pits situated nearer antennal fossae than mandibular insertions. Frontal lobes sinuate, divergent posteriad. Weak psammophore present. Palp formula 2,2. Mandibular teeth three, plus minute, basal denticle or angle; mandibles with sub-parallel inner and outer margins, striate; masticatory margin of mandibles approximately vertical or weakly oblique; basal tooth a small to minute denticle or angle, much smaller than t3 (four teeth present).

MESOSOMA: Promesonotum shining and smooth on dorsum, lower mesopleuron strongly punctate; (viewed in profile) promesonotum broadly convex anteriad, convexity reduced posteriad; promesonotal setae seven to twelve; standing promesonotal setae a mixture of well-spaced, distinctly longer, erect and semi-erect setae which are curved distally and often paired, interspersed with much shorter, incurved, decumbent setae; appressed promesonotal setulae well-spaced over entire promesonotum. Metanotal groove strongly impressed, with distinct transverse costulae. Propodeum uniformly finely striolate, some punctation on metapleuron; propodeal dorsum flat throughout most of its length; propodeum smoothly rounded or with indistinct angle; standing propodeal setae variable in number and arrangement, when present usually one prominent pair at propodeal angles or at midlength, with other shorter setae very sparse or absent; appressed propodeal setulae well-spaced and sparse; propodeal spiracle equidistant from metanotal groove and declivitous face of propodeum. Vestibule of propodeal spiracle distinct in some specimens. Propodeal lobes present as vestigial flanges or small strips of cuticle only.

PETIOLE AND POSTPETIOLE: Petiolar spiracle lateral or laterodorsal and situated within anterior sector of petiolar node or just at front of node; node (viewed in profile) conical, vertex rounded; appearance of node shining and smooth throughout; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) between 1:1 and 3:4; anteroventral petiolar process absent or vestigial; ventral petiolar lobe absent; height ratio of petiole to postpetiole between 1:1 and 3:4; height–length ratio of postpetiole between 4:3 and 3:4; postpetiole shining and smooth; postpetiolar sternite without anterior lip or carina, or this structure vestigial.

GASTER: Pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with a few appressed setulae.

MESOSOMA: Color yellow-orange to brownish-orange, gaster chocolate with or without yellowish area on anterior sector of first gastral tergite. Worker caste monophasically allometric, i.e., with variable size, but not morphology among workers from same nest.

LECTOTYPE MEASUREMENTS (M. basale): HML 1.70 HL 0.66 HW 0.58 CeI 88 SL 0.48 SI 83 PW 0.34.

LECTOTYPE MEASUREMENTS (M. vexator): HML 1.78 HL 0.68 HW 0.62 CeI 91 SL 0.50 SI 81 PW 0.36.

OTHER WORKER MEASUREMENTS (non-types): HML 1.31–1.92 HL 0.49–0.76 HW 0.38–0.68 CeI 78–89 SL 0.39–0.52 SI 76–103 PW 0.25–0.40 (n=20).

Queen
Heterick (2006) - HEAD: Head rectangular; vertex weakly concave or planar; frons shining and smooth except for piliferous pits and striolae around antennal sockets, frontal carinae and below the eyes, and fine rugulae near posterior margin of vertex; frons consisting mainly of decumbent setae, with two longitudinal, parallel rows of erect setae straddling the midline. Eye elongate, elliptical and oblique; (in full-face view) eyes set above midpoint of head capsule; (viewed in profile) eyes set posteriad of midline of head capsule.

MESOSOMA: Anterior mesoscutum smoothly rounded, thereafter more-or-less flattened; pronotum, mesoscutum and mesopleuron shining and mainly smooth, vestigial striolae, if present, confined to anterior katepisternum; length–width ratio of mesoscutum and scutellum combined between 7:3 and 2:1. Axillae a strip of thin cuticle separating mesoscutum and scutellum, each individual axilla indistinct. Standing pronotal/mesoscutal setae a mixture of well-spaced, distinctly longer, erect and semi-erect setae which are curved distally, interspersed with much shorter, incurved, decumbent setae; appressed pronotal, mescoscutal and mesopleural setulae abundant, particularly on mesoscutum. Propodeum shining and smooth, with a few weak striolae on metapleuron; always smoothly rounded; propodeal dorsum convex; standing propodeal setae consisting of one pair anteriad, with or without another pair posteriad; propodeal spiracle nearer metanotal groove than declivitous face of propodeum; propodeal lobes present as vestigial flanges only, or absent.

WING: Wing not seen (queen dealated).

PETIOLE AND POSTPETIOLE: Petiolar spiracle lateral and situated slightly anteriad of petiolar node; (viewed in profile) node conical, vertex rounded; appearance of node shining and smooth; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) about 1:1. Anteroventral petiolar process absent or vestigial; height ratio of petiole to postpetiole between 4:3 and 1:1; height–length ratio of postpetiole between 4:3 and 1:1; postpetiole shining, with vestigial sculpture; postpetiolar sternite with anterior and posterior margins convergent, forming a narrow wedge.

GASTER: Pilosity of first gastral tergite consisting mainly of appressed setae with a few erect and semi-erect setae.

GENERAL CHARACTERS: Color of foreparts tawny-yellow, gaster brown. Brachypterous alates not seen. Ergatoid or worker-female intercastes not seen.

QUEEN MEASUREMENTS: HML 3.22–3.46 HL 0.83–0.84 HW 0.76–0.80 CeI 92–95 SL 0.60–0.62 SI 78 PW 0.68–0.89 (n=2).

Type Material
Heterick 2006:

Atta destructor Jerdon 1851:105. Syntype ☿'s, INDIA [no types known to exist].

Myrmica basalis Smith 1858:125. Syntype ☿ (lectotype here designated), SRI LANKA [examined].