The horse had been in a one-eighth acre paddock, isolated on three sides. The horse and paddock were treated March 3, and the horse received a second treatment March 6. It was released from quarantine March 15. Horses in adjacent paddocks were examined, and no wounds were discovered on those animals. The National Veterinary Services Laboratories reported that the larvae in the infested horse were in the third instar stage, at least 24 hours from maturity.
Mature larvae drop from the wound and pupate in the soil for approximately one week.
Then it takes approximately one more week for the flies to become sexually active. The screwworm is found in subtropical and tropical climates. In the 1930s there was a serious outbreak in the southern United States, with more than 1.3 million cases of infestation and the death of more than 200,000 animals. The United States has been free of screwworms since 1966. In the early 1950s the USDA Agricultural Research Service developed a method of eradication using sterile flies to cause the species to breed itself out of existence.