The theraphosid Nesiergus insulanus is a member of a genus endemic to the Seychelles archipelago. Very little is known about the finer-scale distribution, density, and total population size of the species, knowledge of which is essential for conservation purposes. We used transect sampling to estimate these variables on Frégate Island. We show that the species is widely distributed, but geographically restricted as a result of fragmentation due to human activity. Where found, densities can be very high (>100 m-2). The total population on the island was estimated to be well over 100,000, although limitations to dispersal ability may be of conservation concern.