Myrmelachista longiceps Longino 2006

Formicinae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia

worker face view

worker lateral view

queen face view

queen lateral view

Queen in images above is holotype.

Additional images:

Holotype queen, lateral view with wings (large); label (large). Male, face view (large). Different male, abdomen, lateral view (large); genitalia (large). Different male, genitalia (large); apex of digitus (large). Different male, genitalia (large).


Costa Rica. In Costa Rica it occurs throughout the country in mature wet forest habitats, most commonly from 500-1500m elevation but occasionally lower.


Diagnosis: Worker with antenna 9-segmented, color red brown. Queen with head black, elongate, CI 80-86. Male with digitus usually long and paddle-shaped with thickened posterodorsal margin.

Worker: Antenna 9-segmented; maxillary palpus 5-segmented but terminal segment elongate, sometimes with partial constriction suggestion partial fusion of terminal two palpomeres; dorsal surface of mandible weakly to strongly rugose or punctatorugose; clypeus and face smooth and shining with variable amount of roughening and larger puncta on anterior malar spaces and anterior clypeus; in full face view, side and rear margins of head with sparse to abundant appressed to subdecumbent pubescence, sometimes with a few projecting setae on posterolateral vertex; ventral surface of head with sparse to abundant short subdecumbent pubescence, no erect setae; scape with abundant suberect setae, longer setae about equal to width of scape; hind tibia with abundant appressed to subdecumbent setae, relatively uniform length, short, about 1/4 width of tibia; typically with dark brown head and gaster, mottled dark and light brown mesosoma, sometimes uniformly dark brown, never strongly bicolored.

Measurements: HL 0.593-0.779, HW 0.562-0.716, SL 0.312-0.384, EL 0.127-0.147, CI 89-95 (n=5).

Queen: Antenna 9-segmented; maxillary palpus 5 or 6-segmented; dorsal surface of mandible moderately to strongly punctatorugose; clypeus and anterior malar spaces roughened and with large puncta, grading to smooth and shining with smaller puncta posteriorly; in full face view side and rear margins of head with abundant short appressed to suberect pubescence, without longer erect setae, sometimes with longer erect setae on posterolateral vertex; ventral surface of head with abundant subdecumbent to suberect setae, these similar to or longer than setae on sides of head; scape with abundant suberect setae, longer setae about equal to width of scape; hind tibia with abundant appressed to suberect setae, relatively uniform length, short, about 1/4 width of tibia; color largely black, sometimes with some degree of lighter red color on anterior face.

Measurements: HL 1.096-1.270, HW 0.904-1.078, SL 0.470-0.551, EL 0.281-0.330, OW 0.045-0.079, OD 0.187-0.232, CI 80-86, OI 29-33, OcI 4-7 (n=10).

Male: Antenna 10-segmented; maxillary palpus 5 or 6-segmented; pygostyles absent; basiparamere with long, needle-like lobe; paramere very elongate and linear, with parallel sides; apodeme of penial valve curving into dorsal margin at obtuse angle. Volsella variable as follows: (collection JTL2280) cuspis very short, closely applied to inner surface of paramere, paddle-shaped, apex with a row of small denticles, only apical row of denticles sclerotized; digitus with short, narrow, downcurved base where dorsal margin close to cuspis, then expanding into large paddle-shape structure, dorsal margin revolute and thickened, forming bulla, large lamina of digitus with several irregular thin spots; (JTL2696) cuspis very short and narrow, parallel sided, distant from digitus, digitus broadly and bluntly scimitar-shaped, but not as grossly expanded, without revolute margin or bulla, irregular thin spots small, faint; (JTL2620) cuspis like JTL2696; digitus like a shorter version of JTL2696, with apical margin greatly thickened and forming pair of bulla, shiny and cream-colored on dried specimen; lamina of digitus lacking thin spots.

Natural History

This species occurs in mature wet forest habitats, most commonly in montane forests but occasionally lower. It nests in live stems of various plant species. Nests have been found in the live stems of a 2m tall shrub in the Rubiaceae, a large Palicourea-like shrub, Guarea rhopalocarpa, Ocotea, Licaria, Ocotea whitei, Conostegia, and Ficus. Founding queens have been found in Guarea (the undescribed species usually inhabited by M. flavoguarea), in chambers in terminal shoots of sprouts from the base of a G. rhopalocarpa tree, in a small Inga sapling (adjacent to a large mature colony in a Licaria tree), and in a shrub in the Rubiaceae. Coccoidea often occur in the stems.


One collection is very similar to longiceps in many respects, but is an outlier with respect to queen size. The queen is much smaller than any longiceps queen. It is currently assigned the morphospecies code JTL-022. It is based on one collection from Refugio Eladio in the Pe–as Blancas Valley, Cordillera de Tilar‡n, Costa Rica. Workers and queens were collected from live branches of a Lonchocarpus tree that had been knocked over by a small landslide. The colony was polygynous, with many dealate queens. There were also Coccoidea with the ants in the stems. The measurements of a queen from this collection are: HL 0.914, HW 0.715, SL 0.416, EL 0.237, OW 0.040, OD 0.178, CI 78, OI 33, OcI 4 (n=1).

Literature Cited

Longino, J. T. (2006). A Taxonomic review of the genus Myrmelachista (Hymenoptera: Formicidae) in Costa Rica. Zootaxa 1141:1-54.

Page author:

John T. Longino, The Evergreen State College, Olympia WA 98505 USA.

Date of this version: 20 March 2006.
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