Abstract The maintenance of sociality is most difficult to explain under circumstances where non-reproducing helpers are physiologically capable of reproducing and distantly related to the brood they rear. The Neotropical swarm-founding wasps are likely to fulfil these conditions because most taxa lack morphological differences between workers and queens, and they have many queens per nest, which is expected to substantially lower worker to brood relatedness. No morphological differences between workers and queens in Parachartergus colobopterus were detected. Colonies contained an average of 27 queens. However, relatedness among nestmates in P. colobopterus was higher ( r=0·31) than would be expected on the basis of queen number alone because the queens themselves are very closely related ( r=0·67) and because of large variation in numbers of queens among colonies. This makes the harmonic mean of queen number (five queens), which is the appropriate measure for investigating the impact of queen number on relatedness, much lower than the arithmetic mean. Reproductive dominance of one or a few queens within colonies was not a factor that greatly increased relatedness among workers. Taken together, these results support the cyclical oligogyny hypothesis for the maintenance of sociality in Neotropical social wasps.