The Nesomyrmex echinatinodis species complex occurs as three separate species in Costa Rica. The three species differ in morphology, habitat preference, and colony structure.
Nesomyrmex echinatinodis s.s. has the face shiny, with reticulate-rugose sculpture restricted to the cheeks. The fourth abdominal tergite is smooth and shining. This species is found in mature wet forest areas. It develops large, polydomous colonies with many thousands of workers. In branch falls or fresh treefalls they may be conspicuous, forming columns of workers. I have collected it at Corcovado National Park, Carara Biological Reserve, Alto Palma just southwest of San Jose, Manuel Antonio National Park, Pitilla Station in the Guanacaste Conservation Areea, La Selva Biological Station, and Hitoy Cerere Biological Reserve. At La Selva it is a relatively common element of the arboreal fauna. It occurred in 7 of 52 canopy trees fogged by Project ALAS. In the floodplain of the Rio Cerere I observed a colony nesting in Acacia ruddiae. These are medium size trees that have swollen stipular thorns much like the ant acacias, but lacking food bodies or any specialized ant inhabitant. The colony occupied many of the thorns on a tree in which I was collecting. I collected the entire contents of a pair of dead thorns, and they contained 37 adult workers, 4 adult males, 1 queen with tattered wing stubs, and brood. The brood was concentrated in one of the thorns. The queen with tattered wing stubs suggests polygyny, with adoption of daughter queens. At Alto Palma I found a colony in one internode of a Cecropia obtusifolia sapling along the roadside. It contained 134 adult workers, 1 adult male, 1 dealate queen, and abundant brood of all sizes. At Corcovado I observed workers tending membracid nymphs on Acalypha diversifolia.
Nesomyrmex dalmasi has more extensive sculpture on the face, with faint longitudinal etchings extending up the sides. The fourth abdominal tergite is either smooth and shining or very faintly shagreened anteriorly. I have collected it in Corcovado National Park, Carara Biological Reserve, La Pita at 200m elevation on the road to Monteverde, and at La Selva Biological Station. Thus it is broadly sympatric with echinatinodis in Costa Rica. Collections have all been from scrubby vegetation, roadsides, regenerating pastures, and other early successional habitats, usually as isolated workers. They are not at all conspicuous and occur in very small colonies. In Carara I found a nest in a 6mm diameter dead stick. At La Pita I found a small nest in a dead knot in a guava tree (Psidium). At La Selva I collected a nest in a node of a Cordia alliodora tree. The tree was in a small demonstration forestry plot in open second growth vegetation.
Nesomyrmex JTL-008 has yet more extensive sculpturing, with the face entirely punctatorugose and the fourth abdominal tergite strongly shagreened anteriorly. I have only one collection of this species, from Palo Verde Biological Station in seasonally dry northwestern Costa Rica. A sprawling vine was common along the river bank. The stems had soft pith and were often inhabited by ants. A small Nesomyrmex nest occurred in one of the live stems.
I have several collections of queens, some associated with workers and others not. So far I have not been able to find any distinguishing characters among the queens that would allow me to identify them to species.