Kugler and Brown (1982) stateE. gibbum is similar to E. ruidum and has been confused with it in the past. ... The two species are sympatric over a wide area of lowland, wet Central America, stretching at least from Honduras to Costa Rica. At the gibbum type locality, the Finca La Selva Station of the Organization for Tropical Studies in Costa Rica, E. ruidum is common foraging on the bare ground in the laboratory clearing; E. gibbum occupies the rain forest less than 50 m away from the clearing and is the dominant Ectatomma in the forest. E. ruidum has not been found inside this forest, either by ourselves in general and Berlese-funnel collecting or by Monte Lloyd through wood-block trapping on the forest floor. The same situation seems to hold at Lancetilla in Honduras; but in Panama, in forest on Barro Colorado Island and elsewhere near the Canal, E. ruidum occurs in both clearings and ... in the shady parts of wet forest, whereas E. gibbum has yet to be found in Panama. Thus it appears that E. gibbum vs. E. ruidum may represent an interesting case of ecological displacement.
I have observed E. gibbum at La Selva and in Corcovado National Park. The workers appear more timid than E. ruidum, and quickly drop from vegetation when disturbed. I observed one nest entrance of E. gibbum in Corcovado. It was a slanting tunnel surmounted by a 5mm high turret of packed soil, 17mm outside diameter, 4mm inside diameter. It was in open ground, away from trees or erect stems. I moved a leaf that was by the entrance to a spot 4cm away. A returning worker spent a few seconds searching around that leaf before finding the nest entrance.
Costa Rica, Nicaragua, Honduras. Costa Rica: lowland wet forest of both slopes.
