Unlike common blowflies, screwworm larvae feed on living tissue. Knowing the stages tells you when to scan, when to report, and why the sterile-fly strategy works.
A female lands at the edge of a fresh wound, navel, or body opening and lays a tight, shingle-like mass of eggs — often 200–300 at a time.
Field note: Any open wound on livestock is a landing pad. This is why daily wound scans matter most around calving, branding, and tagging.
Why this matters: a female mates only once — so flooding the area with sterile males makes her eggs fail. That single biological fact is what eradicated screwworm from the U.S. in 1966.
Educational illustration — not to scale. Stage durations vary with temperature. This is awareness guidance, not veterinary diagnosis. Report suspected cases to a veterinarian, state animal-health official, or USDA.