Wolbachia are a group of cytoplasmically inherited bacteria that cause reproduction alterations in arthropods, including parthenogenesis, reproductive incompatibility and feminization of genetic males. Two major subdivisions of Wolbachia (A and B) occur. Wolbachia are found in a number of well-studied insects, but their overall distribution in arthropods has not been well studied. A survey for Wolbachia in 157 Panamanian neotropical arthropod species was done using a polymerase chain reaction assay. Wolbachia were detected in 26 of 154 insect species (16.9%) and zero of three arachnids (0%). Extrapolating to the estimated total number of insect species present globally (10—30 million), an estimated 1.69—5.07 million insect species are infected with these bacteria, making Wolbachia an extremely abundant bacterial group. Wolbachia were found in each of the major insect orders examined, including Coleoptera (6/57 infected), Diptera (5/14), Hemiptera/Homoptera (1/7), Hymenoptera (6/23) Lepidoptera (7/43) and Orthoptera (1/8). Of the 26 positives, eight species were found to be singly infected with A group Wolbachia, nine singly with B group Wolbachia and nine doubly infected with both A and B group Wolbachia. Double infections occur at significantly higher frequencies than expected by chance. The abundance of Wolbachia further supports their potential importance as a mechanism for rapid speciation in insects.