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How to tell Acromyrmex from Atta:
How to tell Acromyrmex from Trachymyrmex:
No easy way. If you have a nest series, Acromyrmex are polymorphic (have workers of different sizes) and the colonies are generally much larger. Trachymyrmex workers are monomorphic (all more or less the same size) and colonies are small. If you have only one or a few workers, see if they match one of the Acromyrmex species. If they do not, go to Trachymyrmex.
a. Median pronotal spines usually present and distinct, occasionally reduced or absent; head tapering behind eyes; head width less than or equal to 1.7mm (common in montane habitats such as Monteverde, Atlantic slope above 500m, Zurqui): coronatus
b. Median pronotal spines usually absent, occasionally present as low tubercles, never distinct spines; head not tapering behind eyes; head width less than or equal to 3.2mm: octospinosus complex
There are subtle patterns of morphology correlated with geographic and behavioral characteristics that suggest three Costa Rican species in the octospinosus complex, but I have not been able to discover satisfactory diagnostic characters that will allow unambiguous identification of single workers. I use the following general patterns in the recognition of the three species.
Propodeal spines carinate, irregularly ridged to tip; distinct pair of short, setose carinae on dorsal face of propodeum anterior to spines; all spines and tubercles generally thinner and sharper; color red to yellow-brown; occurs in open dry habitats such as seasonal parts of Guanacaste province and urban areas in San Jose: echinatior
Propodeal spines smoothly or irregularly conical, not carinate; dorsal face of propodeum with pair of indistinct blunt setose tubercles anterior to spines; all spines and tubercles generally thicker, more blunt; workers of all sizes red to yellow-brown; head width less than or equal to 2.7mm; occurs in Atlantic wet forest and nests on the ground: octospinosus
Sculptural features like octospinosus but major workers dark brown to black (smaller workers may be red to yellow-brown like octospinosus); head width less than or equal to 3.2mm; occurs in Atlantic wet forest; in lowlands, where sympatric with octospinosus, has arboreal nests: volcanus
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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