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Pests of animals: Screw-worm fly
Screw-worm fly (Chrysomya bezziana)
Screw-worm fly has flesh-eating maggots that infest and can even kill animals and people. While it’s not in Australia, if it became established here, it could cost our livestock industries close to $500 million a year in lost production and control measures, and would have a devastating effect on our northern livestock industry. Spread of this pest from Papua New Guinea is one of the major quarantine threats to northern Australia.
Keep a Top Watch
Report incidents of animals transported illegally from Papua New Guinea. Check wounds on all animals for maggots - even small wounds. If you find maggots, collect some and kill them with boiling water, then preserve them in three parts methylated spirit to one part water. Note the location, number, type, age and origin of the animals, and contact Quarantine immediately.
Profile: The screw-worm fly lays up to 250 eggs on a wound or opening in a warm-blooded animal. When the eggs hatch, maggots crawl into the wound and make it bigger by feeding on the living flesh. Small scratches, branding marks or castration wounds can all be affected, and one injury can be struck many times. The fly can infest people as well as animals.
Identification: The fly looks just like an Australian blowfly with a shiny blue-green body and a yellow face. You may not be sure if a fly is a screw-worm fly, but if you look closely at a fly-struck animal you‘ll see live maggots deep in the wound. After six or seven days, the maggots drop out and grow into pupae with a hard brown oval shell.
Photos below: A screw-worm fly lays its eggs in an open wound. The fly can infest people and animals.
Distribution: It is found in the coastal swamps of Papua New Guinea that border the Torres Strait, as well as in Indonesia. A similar fly has been eradicated in the US at great cost, but it is still found in many countries south of Mexico.
Threat: The flies can multiply quickly – maggots hatch within 24 hours. Animals die from loss of tissue fluid and infection. If the fly were to establish in Australia, it would have disastrous effects on our livestock industry (particularly cattle and sheep), but could also threaten our native wildlife.
Quarantine: AQIS distributes screw-worm fly detection kits to pastoralists and vets throughout northern Australia, so they can submit maggots from struck animals for checking. Kits are free – contact your local Quarantine officer for one. Traps are placed at strategic locations, such as airports and seaports, and checked regularly for screw-worm flies. Sentinel cattle herds are used to monitor for maggots.