The longevity, sexual aggressiveness, mating capacity, and mating competitiveness of 4 strains of screwworms, Cochliomyia hominivorax (Coquerel), were evaluated in the laboratory to determine their suitability for mass production, sterilization, and release into the native population. A Texas strain of limited geographical origin was the most laboratory-adapted strain; a Texas strain and a Texas-Mexico strain of extensive geographical origins were the least; a Mexico strain of limited geographical origin was intermediate.