Sphaeropthalma pensyluanica reared from cocoons of the organ pipe mud dauber, Trypoxylon politum from Georgia over several years yielded only adult males. Possible explanations for this sex-biased emergence from this host are (1) obligatory heteronomous heterotrophy, in which the two sexes develop on entirely different hosts; (2) differential mortality in the immature stage, with female larvae dying during development; and (3) facultative size- dependent sex allocation, with female eggs laid only on hosts smaller than T. politum