Monomorium emarginatum

Previous literature records (Wheeler, 1916) indicate that this species prefers to nest in sandy or gravelly soil with tumuli forming tiny craters. Details of nest architecture and biology are unknown. Although the collections of this species are sporadic in the northeastern United States, it appears to be the only species which occurs there. Since workers could be easily mistaken for M. minimum, I assume this was the species that Wheeler (1916) discussed. Unfortunately, he did not collect any queens during his study and workers are difficult to separate, It is possible this species occurs sympatrically with M. viridum in coastal areas. (DuBois 1986)

Identification
DuBois (1986) - A member of the Monomorium minimum species group. Queen: Winged; mesonotum with notal furrow; mandible with 4 teeth, basal tooth reduced. Worker: Propodeum not angular; mesopleuron not punctate; 4-6 erect setae projecting above dorsal outline of alitrunk; PI 34-42 (37).

This species is most likely to be confused with Monomorium minimum and Monomorium viridum. Queens of M. minimum can be separated from those of M. emarginatum since the latter possess a furrow 0n the mesonotum. Queens of M. viridum can be separated from those of M. emarginatum since the petiole and postpetiole of the former are always emarginate while those of the latter are not. Additionally, M. marginatum queens have less facial sculpturing. Workers of M. emarginatum can be separated from both these species since the basal face of the propodeum is shorter than the declivitous face.

Distribution
Scattered localities throughout the northeastern United States.

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

Nomenclature

 *  emarginatum. Monomorium emarginatum DuBois, 1986: 101, figs. 111-118 (w.q.) U.S.A.

Worker
Head: (representing separate localities; N: 5) HL 0.44-0.51 (0.48), HW 0.38-0.44 (0.41), SL 0.28-0.41 (0.35), EL 0.09-0.10 (0.09), MOD 0.06 (0.06). Structure—C180-87 (84), SIL 64-80 (72), SIW 74-93 (86). Scape not surpassing occiput. Sculpture—Head smooth and shining with small piliferous punctures evenly distributed. Alitrunk: Measurement: PW 0.22-0.29 (0.26), PL 0.18-0.21 (0.19), WL 0.49-0.62 (0.53). Structure—Anterior propodeal suture of moderate depth. Propodeum rounded, basal face 2/3 as long as declivitous face. P1 34-42 (37). Pilosity—Dorsal outline of alitrunk with 4-6 erect setae projecting above dorsal outline. Sculpture—Anterior propodeal suture with short, parallel, longitudinal rugae; lower 1/3 of side of propodeum (below spiracle) with small, sometimes faint, parallel, longitudinal rugae. Petiole: Dorsum of node flat to slightly convex. Setae erect on dorsum of node, remainder bare. Color: Head dark brown except as follows: antenna and mandible yellow-brown to brown. Alitrunk brown, legs brown to yellow-brown. Petiole, postpetiole, and gaster brown to dark brown. All setae yellow.

Queen
As described for Monomorium viridum except as follows. Head. (representing different localities; N=6) HL 0.71-0.80 (0.74) {0.80}, HW 0.69-0.81 (0.75) {0.81}, SL 0.52-0.64 (0.58) {0.62}, IOD 0.16-0.18 (0.17) {0.18}, OD 0.05-0.06 (0.05) {0.05}, EL 0.15-0.19 (0.18) {0.19}, MOD 0.09-0.12 (0.11) {0.12}. Structure—Head as broad as long, C196-106 (101) {101}, distinctly longer than scape, SIL 68-86 (78) {78}; SIW 68-88 (77) {76}. Scape not surpassing occiput.{Holotype lacks left antenna}. Mandible with 4 teeth, basal tooth reduced. Sculpture—Moderate, faint, parallel, longitudinal rugae beginning along lateral margin of clypeus, extending past antennal insertion, and converging with frontal carinae. Large to moderate, piliferous punctures evenly distributed. Alitrunk: Measurement: PW 0.58-0.66 (0.62) {0.58}, PL 0.29040 (0.34) {0.40}, WL 1.26-1.65 (1.52) {1.52}. Structure—Mesopleural suture straight with small pit on posterior end. Metanotum (in lateral View) not projecting to level of propodeum and scutellum. PI 20-26 (23) {26}. Wings present {lacking on holotype}. Sculpture—Smooth and shining with moderate piliferous punctures except as follows: lower 1/3 of propodeum (below spiracle) with moderate to large, parallel, longitudinal rugae. Petiole. All surfaces smooth and shining (moderate piliferous punctures where applicable) with small non-piliferous punctures (leading to a granular appearance) along lower 1/2 of side. Postpetiole: Dorsum of node flat. Setae appressed to decumbent on anterior surface of node, decumbent to suberect on dorsum, erect 0n posterior surface and side of node, absent elsewhere. Postpetiolar surface smooth and shining with small piliferous punctures throughout. Color: Head dark brown to brown except as follows: antenna, mandible, and lateral margin of clypeus brown to yellow. Alitrunk dark brown to brown, legs brown to yellow-brown. Petiole, postpetiole, and gaster dark brown to brown. All setae yellow.

Type Material
Virginia. Rappahannock Co.; Amissville 3.2 km W, June 21, 1957, W. L. Brown, Jr., & E. O. Wilson. Holotype queen bears red, handwritten label: Monomorium emarginatum Holotype M. DuBois 1983. Paratypes: Brewster, Cape Cod - 1 queen, 3 workers [MCZ], Woods Hole - 2 queens, 4 workers. All paratypes bear blue, handwritten labels: Monomorium emarginatum Paratype M. DuBois 1983.

Etymology
This species is named for the furrow (emargination) on the mesonotum.