Formicinae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
Additional images: Dark series, face view, worker (small) (large), queen (small) (large). Different queen (large). Different queen (large). Male, face view (large); genitalia (large). Myrmelachista costaricensis syntype worker, face view (large); lateral view (large); dorsal view (large); label (large). Syntype male, face view (large); dorsal view genitalia (large); lateral view genitalia (large); label (large).
Costa Rica. In Costa Rica it occurs throughout the country, from sea level to 1400m elevation cloud forest.
Diagnosis: Worker and queen with 9 antennal segments; maxillary palpus of worker 5-segmented; queen mandible and clypeus largely smooth and shining; queen HL 0.67-0.82mm, CI 85-90; queen often sharply bicolored, with red orange head and mesosoma, dark gaster (occasionally uniform dark red brown); worker HW up to 0.6mm; worker in full face view with pilosity on side of head fully appressed, with no projecting setae or erect pubescence; basiparamere of male with very short, subtriangular lobe, or lobe absent; paramere elongate and linear, with parallel sides; cuspis completely absent; digitus elongate, curving, scimitar-shaped.
Worker: Antenna 9-segmented; maxillary palpus 5-segmented (may be 6-segmented in very large workers); mandible, clypeus, and face smooth and shining (mandible may be weakly striate in very large workers); in full face view, side and rear margins of head with very sparse, very short, fully appressed to subdecumbent pubescence, no projecting erect setae; ventral surface of head with very sparse, very short subdecumbent pubescence, no erect setae; hind tibia usually with sparse, appressed pilosity, occasionally more abundant and subdecumbent, pilosity short, about 1/4 width of tibia; typically bicolored, with orange red head and mesosoma, dark brown gaster, but in montane wet forest areas may be completely dark red brown.
Measurements: HL 0.432-0.539, HW 0.418-0.512, SL 0.225-0.281, EL 0.102-0.119, CI 92-97 (n=5).
Workers of plebecula and joycei cannot always be distinguished.
Queen (previously unknown): Antenna 9-segmented; maxillary palpus 5 or 6-segmented, with varying degrees of fusion of terminal two palpomeres; mandible and clypeus largely smooth and shining with sparse small piligerous puncta; face entirely smooth and shining; face, sides of head, and ventral surface of head with sparse short appressed to subdecumbent pubescence, longer erect setae sparse, 6-8 across posterior margin of vertex, a pair at about mid-face, about 5 on clypeus; hind tibia usually with sparse, appressed pilosity, occasionally more abundant and subdecumbent, pilosity short, about 1/4 width of tibia; coloration often bicolored, with light red orange head and mesosoma, contrasting dark brown gaster; grading to forms with uniform red brown coloration.
Measurements: HL 0.674-0.815, HW 0.601-0.696, SL 0.330-0.385, EL 0.197-0.227, OW 0.032-0.056, OD 0.127-0.166, CI 85-90, OI 32-35, OcI 4-7 (n=9).
Male: Antenna 10-segmented; maxillary palpus 6-segmented; pygostyles minute, in the form of weakly sclerotized papillae without setae; basiparamere with very short, subtriangular lobe or lobe completely absent; paramere elongate and linear, with parallel sides; cuspis completely absent; digitus elongate, curving, scimitar-shaped; apodeme of penial valve curving into dorsal margin at obtuse angle.
This species occurs in a wide variety of habitats, from moist to wet forest, lowlands to mid-montane elevations, weedy roadside vegetation, second growth forest, or mature forest. It is nearly always in highly insolated areas, being relatively common near ground level in scrubby vegetation but restricted to the high canopy in mature forest.
Nests are in narrow galleries in dead or live stems of a variety of plant species. The dead stems are usually narrow gauge, hard, and woody, not fibrous. Colonies may be polydomous, occupying multiple dead or live stems in a tree or shrub. I have found colonies nesting in live stems of Cordia alliodora, Cecropia obtusifolia, Callophylum brasiliense, Sloanea, and Ficus. It is unknown whether workers do any excavation of galleries on their own or just occupy preexisting chambers in myrmecophytes or chambers left by stem-boring insects.
Workers can be observed foraging on exposed stem and trunk surfaces in full sun, often moving in files. Pseudococcidae may occur in nest chambers in live stems.
Alate queens may be in nests at any time of year. Alate queens have been collected in Malaise traps and one was collected at a blacklight sheet.
Longino, J. T. (2006). A Taxonomic review of the genus Myrmelachista (Hymenoptera: Formicidae) in Costa Rica. Zootaxa 1141:1-54.
Menozzi, C. (1927). Formiche raccolte dal Sig. H. Schmidt nei dintorni di San Josˇ di Costa Rica (Schluss). Entomologische Mitteilungen 16, 336Š345.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. firstname.lastname@example.org
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