We studied the structure and placement of retreats of the tarantula Ephebopus murinus (Walckenaer, 1837) in the field in French Guiana. We found that early-instar spiderlings construct above-ground silken tubular retreats among low vegetation, and shifted to a fossorial lifestyle when subadult. Discriminant analysis of microhabitat variables associated with each class of retreat demonstrated that each was predicted by different habitat features. The location of above-ground retreats was predicted by the presence of the terrestrial bromeliad Bromelia spp., whereas leaf-litter predicted the placement of the burrows. This is one of the few examples of an ontogenetic habitat shift (OHS) in a spider. OHS has been suggested to fulfill an ecological function by reducing cannibalism and intraspecific competition. Ephebopus is a fossorial tarantula genus in an otherwise arboreal subfamily. Because of this we suggest that the fossorial lifestyle of subadult/adult E. murinus has evolved secondarily, with the arboreal habit of the early instars reflecting the ancestral habit. This would be a case where phylogeny, and not ecology, explains OHS.