Monomorium compressum

This species nests under stones (Wheeler, 1914b) but nest architecture is unknown. Colonies of M. compressum may have multiple, functioning queens (Wheeler, 1914b).

Identification
DuBois (1986) - Queen Wingless; scutum and scutellum depressed dorsally; metanotum (in lateral view) projecting to level of propodeum and scutellum; propodeum angular. Worker Propodeum angular; mesopleuron not punctate; PI 36-39 (38).

Queens of M. compressum can be distinguished from queens of the other species that occurs in its range (Monomorium cyaneum), since the former have a depressed scutum and scutellum, an emarginate postpetiole, and fewer than 30 erect to suberect setae projecting above dorsal outline of alitrunk. Workers of M. compressum are separated from those of M. cyaneum since the former have a smooth mesopleuron and more than 10 erect to suberect setae projecting above dorsal outline of alitrunk.

Distribution
DuBois (1986) - This species is known from scattered localities across the Mexican Plateau and extending west to the Pacific coast (Morelos and Hidalgo to Sinaloa).

Distribution based on Regional Taxon Lists
Neotropical Region: Mexico.

Nomenclature

 *  compressum. Monomorium minimum subsp. compressum Wheeler, W.M. 1914b: 43 (w.q.) MEXICO. Raised to species: DuBois, 1986: 93.

Worker
Head. (representing different localities; N= 9) HL 0.46-0.55 (0.49), HW 0.37-0.44 (039), SL 0.27-0.40 (0.33), EL 0.08 (0.08), MOD 0.05-0.06 (0.06). Structure—CI 76—87 (80), SIL 54—78 (68), SIW 71-92 (85). Scape reaching but never surpassing occiput. Alitrunk. PW 0.22-0.28 (0.25), PL 0.17-0.24 (0.20), WL 0.44-0.62 (0.54). Structure—PI 36-39 (38). Pilosity—Dorsal outline of alitrunk with 8-14 erect to suberect setae. Petiole. Dorsum of node convex. Setae erect on dorsum of node, remainder bare. Lower 1/3 of side with small, non-piliferous punctures (leading to a granular appearance); remainder smooth and shining (dorsum of node with piliferous punctures). Postpetiole. Posterior 1/3 of postpetiole with dense, non-piliferous punctures; remaining surfaces smooth and shining (dorsum of node with piliferous punctures). Gaster. as in Monomorium minimum Color. Head brown except as follows: base of mandible and antenna yellow brown.

Queen
DuBois (1986) - As described for Monomorium cyaneum except as follows. Head: (representing type locality — probably from same nest; N=3) HL 0.60-0.68 (0.64), HW 0.55-0.60 (0.58), SL 0.45-0.50 (0.48), IOD 0.12—0.14 (0.13), OD 0.02-0.04 (003), EL 0.11—0.14 (0.12), MOD 0.10 (0.10). Structure—CI 80—96 (90), SIL 73-75 (74), SIW 77-91 (83).

Eye small. Pilosity—Setae erect near clypeus, frontal carinae, mandibles and ocelli, decumbent to appressed on malar area, appressed on remainder of head (including gular region). Sculpture—Small parallel rugosities extending from distal portion of clypeus (between clypeal teeth) to level of antenna] insertions between frontal carinae. Alitrunk: Measurements PW 0.38-0.40 (039), PL 0.25-0.28 (0.26), WL 0.88-0.90 (0.89). Structure—Scutum and scutellum depressed. Mesopleural suture deflected ventrally at posterior end (with a small pit on anterior end). Propodeum angular, basal and declivitous faces of approximately equal length. PI 27-32 (29). Pilosity—Dorsal outline of alitrunk with 8-16 erect to suberect setae (projecting over 3/4 their lengths above outline). Petiole: Dorsum of node convex to flat. Anterior surface and side of node with small non-piliferous punctures; dorsum smooth with few piliferous punctures; posterior surface with moderate, transverse, concentric, semicircular rugae. Postpetiole: Dorsum of node convex to slightly emarginate. Dorsum of node smooth (with few piliferous punctures), remaining surfaces with dense nonpiliferous punctures. Gaster. As in Monomorium minimum. COLOR: Head and antenna brown except as follows: base of mandible and lateral margin of clypeus yellow to yellow brown.

Type Material
DuBois (1986) - Syntypic series consisting of “4 females and several workers” (Wheeler, 1914b): MEXICO: Hidalgo: San Miguel [spring or summer, 1913], W. M. Mann (3 queens, 12 workers; ). Lectotype queen here designated from NMNH series bears red, handwritten label: Monomorium minimum compressum Wheeler Lectotype Queen M. DuBois 1983. The lectotype is mounted on same point with 2 workers which could not be removed.