This species occurs in mature wet forest understory. It is an obligate inhabitant of an undescribed species of Guarea (Haber, pers. comm.). Most species of Guarea are large canopy trees; this species is an understory treelet, reaching reproductive maturity at 2-3m height. It is always a single stem from ground to shoot apex, with no lateral branches. Colonies of Myrmelachista occupy the entire stem, from ground level to the shoot apex. At Refugio Eladio in the Pe–as Blancas Valley, the one site where I have collected M. flavoguarea, the tree is moderately common. Nearly every tree I have examined has contained M. flavoguarea, and I have never collected M. flavoguarea in any other situation. Thus, it appears to be an obligate inhabitant of this Guarea species.
There may be one or two physogastric colony queens. Occasional Coccoidea occur inside the stems. The only entrance holes are near the shoot apex. A few workers are occasionally seen on the surface near the shoot apex, but inside the stems are densely packed with hundreds of workers.
The biology of this species appears very similar to M. flavocotea, nigrocotea, lauroatlantica, lauropacifica, osa, and haberi, which are all obligate inhabitants of understory Lauraceae.
Costa Rica. In Costa Rica it is known from one site, at 800m on the Rio Pe–as Blancas in the Cordillera de Tilar‡n.
