In the wasp Trypoxylon malaisei Gussakovskji, mating occurs among siblings that have emerged from the same nest (local mate competition). Although local mate competition theories predict that mothers should produce the minimum number of sons sufficient to inseminate all daughters in each nest, 30% of nests that we examined contained only females, and 5% contained only males. We examined three nest properties (brood size, length of the unoccupied space, and thickness of the outermost wall) to determine whether a nest was complete. All-female nests had smaller brood sizes, larger unoccupied spaces, and thinner outermost walls than mixed-sex nests, suggesting that all-female nests were incomplete. All-male nests had brood sizes and unoccupied spaces similar to those of all-female nests, although the thickness of the walls was inconsistent. We discuss problems arising from the inclusion of incomplete broods in analyzing sex-ratio data.