Key to Myrmelachista queens of Costa Rica

This key is based on: [[Media:Longino 2006a.pdf|Longino, J.T. 2006. A taxonomic review of the genus Myrmelachista in Costa Rica. Zootaxa. 1141:1-54. PDF]]

Longino stated the following about Queen characters:

Queens are often more powerful differentiators of species than workers. The meristic, sculptural, and pilosity characters discussed for workers also apply to queens. Color is a valuable character, often sharply separating species when worker color does not. For example, the species that are specialist inhabitants of Ocotea and Guarea all have relatively uniform yellow workers, yet the queens differ dramatically in color, being either solid orange, solid black, or bicolored. Details of queen head size, head shape, and ocellus size are important for differentiating species.

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 * Myrmelachista
 * Costa Rica

1

 * Antenna with 10 segments; color dark brown to black . . . . . 2


 * Antenna with 9 segments; color variable, from yellow orange to red brown to black . . . . . 4

2
return to couplet #1
 * Mandible strongly falcate; head dorsoventrally flattened . . . . . Myrmelachista cooperi


 * Mandible subtriangular with differentiated basal and masticatory margin; head not strongly dorsoventrally flattened. . . . . . 3

3
return to couplet #2
 * Face weakly roughened or sericeous, not strongly shining; HW greater than 0.8mm . . . . . Myrmelachista zeledoni


 * Face smooth and shiny; HW less than 0.6mm . . . . . Myrmelachista mexicana

4
return to couplet #1
 * Head orange . . . . . 5


 * Head dark red brown to black . . . . . 9

5
return to couplet #4
 * HL greater than 1.2mm (Fig. 6) . . . . . 6


 * HL less than 1.2mm . . . . . 7

6
return to couplet #5
 * Gaster solid dark brown; obligate inhabitant of understory Guarea in Cordillera de Tilarán . . . . . Myrmelachista flavoguarea


 * Gaster yellow orange with narrow infuscated bands medially; non-specialist inhabitant of live stems in Cordillera de Talamanca . . . . . Myrmelachista meganaranja

7
return to couplet #5
 * Sides of head and hind tibia with pilosity (pubescence or longer setae) completely appressed; HL less than 0.85mm (Fig. 6); eyes relatively large, OI greater than 30; ocelli small, OcI 4–7; generalist inhabitant of live and dead stems . . . . . Myrmelachista plebecula (also keys elsewhere due to variability in head color)


 * Sides of head and hind tibia with subdecumbent to suberect pilosity; HL greater than 0.85mm; eye size variable, OI 27–37; ocelli larger, OcI 6–10; specialist inhabitant of understory Ocotea. . . . . . 8

8
return to couplet #7
 * Eyes relatively small, OI 27–31; HW greater than 0.8mm (Fig. 6); Atlantic slope and central Cordilleras . . . . . Myrmelachista flavocotea


 * Eyes larger, OI 33–37; HW less than 0.8mm; southern Pacific lowlands . . . . . Myrmelachista lauropacifica

9
return to couplet #4
 * HW less than 0.7mm (Fig. 7); generalist inhabitant of live and dead stems . . . . . Myrmelachista plebecula


 * HW greater than 0.7mm; specialist or generalist inhabitant of live stems . . . . . 10

10
return to couplet #9
 * HL usually between 0.8–1.2mm (Fig. 7); head relatively broad, CI 87–98; eyes relatively small, OI less than 30, often around 27 (Fig. 8); ocelli very small, OW often less than 0.05mm; mandible smooth and shining or weakly rugose; maxillary palpus always 6–segmented (workers brown to mottled red brown; common cloud forest species nesting in many species of trees) . . . . . Myrmelachista joycei


 * HL between 0.8–1.4mm; CI 79–93; OI 23–33; OW 0.04–0.10mm; mandible punctatorugose; maxillary palpus 5 or 6-segmented. . . . . . 11

11
return to couplet #10
 * HW greater than 1.1mm (Fig. 7); head relatively broad, CI 88–93; eyes relatively small, OI 23–27 (Fig. 8); much of face slightly roughened, dull, not strongly shining (Fig. 9A) . . . . . Myrmelachista nigrocotea


 * HW less than 1.1mm, if approaching 1.1mm then head relatively elongate (CI less than 86); OI greater than 27; most of face smooth and strongly shining. . . . . . 12

12
return to couplet #11
 * In full face view with long erect setae projecting from sides of head (Fig. 9D); maxillary palpus 5-segmented . . . . . Myrmelachista lauroatlantica


 * Sides of head with short appressed to suberect pubescence, no longer erect setae; maxillary palpus 5 or 6-segmented . . . . . 13

13
return to couplet #12
 * Workers dark red brown (longiceps queens bridge the morphological gap between haberi and osa and cannot be distinguished from either) . . . . . Myrmelachista longiceps


 * Workers yellow orange . . . . . 14

14
return to couplet #13
 * Maxillary palpus 5-segmented; CI 83–89; HL 1.00–1.12; sides of head rounding more gradually into rear margin (Fig. 9B) . . . . . Myrmelachista haberi


 * Maxillary palpus 6-segmented; CI 79–84; 1.18–1.23; head more sharply rectangular, sides flat and more abruptly rounding into flat rear margin (Fig. 9C) . . . . . Myrmelachista osa