Camponotus chromaiodes

Camponotus chromaiodes, the “rust-colored carpenter ant” (Smith, 1965) nests in and under rotten wood, including logs and stumps, with the galleries often extending into the soil (often clay soil), as well as in standing dead trees, or in moist, rotten parts of buildings (Hansen and Klotz, 2005). This is a low altitude species which lives in wooded areas as in well-rotted logs and stumps, or standing dead trees (Smith, 1965). MacGown and Brown (2006) reported that it nests in rotten wood and soil at the base of Quercus sp., and it nests in the soil or in rotten logs in Alabama (Forester, 2003). In warm sites, C. chromaiodes tends to occupy relatively heated chambers (Diamond et al., 2012).

Compare with Camponotus herculeanus, Camponotus modoc, Camponotus novaeboracensis, Camponotus pennsylvanicus.

The major and minor workers of C. chromaiodes are usually dark, with a black head and gaster and a partially deep red mesosoma and legs. Nearly all workers and the female have red color on the anterior edge of the gaster. The gaster is covered with golden appressed pubescence, which gives it a somewhat golden sheen; the posterior edges of each tergum are reddish brown. The scapes extend 2 - 3 funicular segments past the posterior lateral corners of the head. The mesosoma, including the side of the propodeum, is covered with scattered, appressed, golden pubescence. The appressed, golden pubescence on the gaster nearly hides the surface and many of the setae are as long as the erect and suberect setae on the gaster.

The female is similar, although much of the mesosoma may be dark in color.

The male is a large, black specimen.

Comparisons
Camponotus chromaiodes and Camponotus pennsylvanicus (eastern US) are nearly identical, differing only in color, with the anterior edge of the gaster being dark reddish brown in Camponotus chromaiodes. The two species co-occur in Douglasville, Pennsylvania and their ranges overlap, which suggests they are valid species. Specimens in which the mesosoma is red and the head and gaster black, without the reddish brown colored anterior section of the gaster are considered to be C. pennsylvanicus.

Occasionally specimens of C. chromaiodes have short appressed setae on the gaster, similar to Camponotus modoc (most common in western US). The two species can be separated as the anterior edges of the gaster of C. modoc is always dark. The setae on the dorsum of the gaster of C. chromaiodes are golden in color, contrasting with the dark gaster, whereas they are similar in color to the gaster in C. modoc, or possibly whitish.

Camponotus chromaiodes can be difficult to separate from Camponotus herculeanus (most of US). Usually the minors, majors and females can be separated by the relatively longer scapes (extend past the posterior corner of the head more than first funicular segment in the major, more than 3 segments in the minor and more than 1 segment in the female, whereas they are generally shorter in the corresponding castes in C. herculeanus, but often in small series, it is nearly impossible to separate them. The setae are usually longer on the dorsum of the gaster in C. chromaiodes, about as long as the semierect setae, whereas they are shorter in C. herculeanus. Females of the two species often have setae of approximately the same length.

Camponotus chromaiodes could be confused with Camponotus novaeboracensis (S Canada, US), but can be separated by the golden setae on the dorsum of the gaster, which are about the same color as the background in C. novaeboracensis.

There is considerable variation in the length of the appressed setae on the dorsum of the gaster of C. chromaiodes, similar to what is found in Camponotus pennsylvanicus and C. modoc, and if we consider the latter two taxa to be separate species, we may find a cryptic species also in what is regarded as C. chromaiodes.

They occur in hickory oak forest, maritime hammock, loblolly pine and hardwoods and in Bocage farmland, hardwood forest, hardwood/pine forest, a clearing in hardwood forest, mixed hardwood forest with pines, pine oak forest, mixed hardwood, larch oak forest, and in hardwood forests. They are also reported from deciduous and mixed forest (MacGown and Brown, 2006), pocosin, swamps/bottomland hardwood, closed canopy evergreen forest/woodland, upland pine forest, pine woodland/long-leaf pine savanna, upland deciduous forest, mesic deciduous forest, upland mixed forest (Davis, 2009), black cherry-red maple forests (Yitbarek et al, 2011) and urban habitats (Guénard et al., 2015).

Distribution based on Regional Taxon Lists
Nearctic Region: United States.

Nest populations range from fewer than 100 to more than 3000 individuals (Smith, 1965), or 3000-12,000 workers (Hansen and Klotz, 2005). The nest is founded by a single female (Smith, 1965) although multiple delate females (up to at least three) may be found in nests.

Foragers are more active at night (A. Lazarus pers. comm.) and can be collected in pitfall traps. Workers feed on small insects, honeydew from homopterans, the juice of fruits and the saps of plants (Smith, 1965).

Sexuals produced during one year may overwinter in the parental nest and have their nuptial flights the following year (Smith, 1965). Alates were found in nests from April - October. Dealate females found nests under bark of logs and stumps from April to July.

Camponotus chromaiodes has the bacterial symbiont Blochmannia chromaiodes (Williams and Wernegreen, 2013), which is an unculturable bacterium that lives exclusively within the cytoplasm of ant cells and supply nutrients such as essential amino acids to their host insects (Fan et al., 2013). They are also the host of the endosymbiotic bacterium Candidatus Blochmannia (Degnan et al., 2004) as well as Wolbachia bacteria (Wernegreen et al., 2009).

It is an alternate host for Nemadus triangulum (Coleoptera: Leiodidae) (Peck and Cook, 2007), a warm climate species which feeds on waste products in nests (Ellison et al., 2012). It is also the host of the ant cricket Myrmecophilus pergandei (Hebard, 1920).

Occasionally C. chromaiodes may nest in wood structures (Forester, 2003), but is apparently not a major house pest (Smith, 1965), although it can be a major structural pest (Hansen and Klotz 2005).

Hölldobler and Engel-Siegel (1984) discuss the lack of the meta-pleural gland in this species.

Nomenclature

 * ferruginea. Formica ferruginea Fabricius, 1798: 279 (w.q.) U.S.A. [Junior primary homonym of Formica ferruginea Christ, 1791: 512.] Replacement name: Camponotus chromaiodes Bolton, 1995b: 92. Wheeler, W.M. 1910d: 338 (s.m.). Combination in Camponotus: Roger, 1863b: 6; in C. (Camponotus): Emery, 1925b: 72. Junior synonym of pennsylvanicus: Roger, 1863b: 6. Revived from synonymy as subspecies of pennsylvanicus: Forel, 1879a: 56. Subspecies of herculeanus: Emery, 1925b: 72; of pennsylvanicus: Creighton, 1950a: 368. Revived status as species: Brown, 1950d: 158.
 *  chromaiodes. Camponotus chromaiodes Bolton, 1995b: 92. Replacement name for Formica ferruginea Fabricius, 1798: 279. [Junior primary homonym of Formica ferruginea Christ, 1791: 512.] [For earlier history of the taxon see under ferruginea Fabricius.]

Type Material
Types not examined by Mackay (2019).

Major worker measurements (mm): HL 2.72 - 2.88, HW 2.60 - 2.96, SL 2.70 - 2.76, EL 0.63 - 0.64, CL 0.86 - 0.95, CW 1.14 - 1.15, WL 3.66 - 3.88, FFL 2.42 - 2.48, FFW 0.69 - 0.73. Indices: CI 96 - 103, SI 96 - 99, CLI 121 - 132, FFI 28 - 29.

Mandible with 5 teeth; anterior border of clypeus straight, carina poorly developed; sides of head narrowed anteriorly, posterior margin of head concave; eyes failing to reach sides of head by ½ to nearly 1 minimum diameter; scape extending about 2 funicular segments past posterior lateral corner of head; 2 faces of propodeum about equal in length, rounded between faces; petiole narrow in profile, apex convex and rounded as seen from front.

Erect and suberect setae sparse, 2 setae along posterior margin of clypeus, several along anterior border of clypeus, absent on cheeks, sides of head, posterior lateral corners, few located between frontal carinae posteriorly to posterior margin, several present on dorsum of mesosoma, petiole and gaster, most setae on tibiae decumbent or appressed, row of bristles extends about ½ distal length of posterior tibia; appressed pubescence sparse on most surfaces, scattered on head, on dorsum of mesosoma, on sides of propodeum, on petiole, dense on gaster, long (0.2 - 0.4 mm, about equal in length to erect and suberect setae), golden in color.

Head densely, finely punctate, dorsum of mesosoma finely coriaceous, sides coriaceous converging to punctate, gaster roughly sculptured, sculpture mostly hidden by appressed setae.

Most usual color combination consists of a black head, black gaster (appearing somewhat golden due to appressed pubescence), mesosoma mostly red, anterior edge of gaster red, antennae black, legs red.

Minor worker measurements (mm): HL 1.88 - 2.33, HW 1.48 - 1.90, SL 2.22 - 2.44, EL 0.46 - 0.53, CL 0.55 - 0.66, CW 0.83 - 0.99, WL 2.70 - 3.12, FFL 1.86 - 2.06, FFW 0.54 - 0.65. Indices: CI 79 - 82, SI 105 - 118, CLI 149 - 150, FFI 29 - 32.

Similar to major worker, differing in that sides of head are convex, about as narrow near mandibles as at posterior lateral corners, posterior margin convex, weakly concave as seen obliquely from above; eyes fail to reach sides of head by about ¼ minimum diameter; scape extends more than 3 funicular segments past posterior lateral corner of head; mesosoma, petiole and gaster as in major worker. Erect and suberect setae, appressed pubescence, sculpture and color as in major worker.

Female measurements (mm): HL 2.88 - 2.96, HW 3.18 - 3.26, SL 2.62 - 2.74, EL 0.80, CL 0.99 - 1.08, CW 1.28- 1.29, WL 4.96 - 5.40, FFL 2.58 - 2.71, FFW 0.74 - 0.79. Indices: CI 110, SI 91 - 93, CLI 120 - 129, FFI 29.

Similar to major worker, except sides of head nearly straight, narrowed posterior to eyes, posterior margin nearly straight; eyes fail to reach sides of head by about ¼ minimum diameter; scape extends 1 – 2 funicular segments past posterior lateral corner of head; dorsopropodeum shorter than posteropropodeum, broadly rounded between faces, propodeal spiracle more than twice as long as broad; petiole narrow as seen in profile, apex flat or slightly concave as seen from front.

Pilosity, sculpture and color as in major worker. Male measurements (mm): HL 1.64 - 1.70, HW 1.54 - 1.64, SL 1.98 - 2.12, EL 0.61 - 0.66, CL 0.48, CW 0.73 - 0.74, WL 3.68 - 4.00, FFL 2.28 - 2.46, FFW 0.49 - 0.55. Indices: CI 94 - 96, SI 121 - 125, CLI 153 - 155, FFI 21 - 22.

Large (over 1 mm total length), black specimen, with brown legs.

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