Abstract. 1. Ecological assemblages frequently show nestedness patterns of species distribution. Despite the common occurrence, the causality for nestedness patterns remains unclear. The effects of environmental and spatial factors on the patterns of insect species distributions were examined on 28 small islands in central Exuma, Bahamas.
2. Flying insects on each island were surveyed by Malaise traps, island area and vegetation height being used as environmental factors, and the degree of island isolation as a spatial factor. Body and relative wing length, and abundance of insect species were also considered as species traits which, together with environmental and spatial factors, determine insect distributions.
3. Island isolation was determined from distance to the mainland, greatest distance in a stepping-stone pathway, distance to the nearest island, and the island area within 250, 500 and 1000 m of each island’s perimeter.
4. The pattern of island-insect nestedness was examined for the overall insect assemblage and those of five dominant insect orders on the islands. The order of island ranking in the nested matrix was tested relative to area, isolation and vegetation height, the rank order of insect species then being examined relative to body and wing length, and abundance of species.
5. Significant nestedness was found in all assemblages. Significant contributions of environmental factors were found in Diptera and Hemiptera assemblages, whereas relatively large contributions of spatial factors were found in Lepidoptera and Hymenoptera assemblages. These results illustrated the need to include spatial factors in analyses on the assembly of insular insect assemblages.