Dead wood of arborescent Euphorbia plants in the Macaronesian islands and Morocco has a diverse fauna of wood-boring beetles. Thirty-eight species were found in four species groups of Euphorbia, including 29 species of scolytine bark beetles, six species of cossonine weevils, two species of Laemophloeidae and one of Monotomidae. All scolytines (but not cossonines and cucujoids) have narrow host preferences, using only one host group for feeding and reproduction. The number of islands on which each species was found was also limited, resulting in geographically distinct guilds for each Euphorbia host. The majority of species (26) were found on the E. lamarckii species complex, followed by E. balsamifera (13) and the succulents E. canariense (12) and E. echinus (3), while only two species were found on the rare montane species, E. longifolia, in Madeira. Up to six or seven species could be found in a single branch of E. lamarckii and E. canariense, respectively, but more than half of the plants had fewer than three species. Putative niche partitioning was indicated by the alternative utilization of different tissues in E. balsamifera and different moisture preferences in the succulent E. canariense. Several unusual features of bark beetle reproductive biology were also observed, including infrequent communal nesting and very small broods. Taken together with the phylogenetic, geographical and biological data now available for most species associated with dead Euphorbia, several of the beetle guilds should provide promising model systems for studying of species interactions and community structure.