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New World Screwworm

REPORT MAGGOTS SEEN IN LIVE OR HARVESTED ANIMALS!

Early detection of New World screwworm is critical to prevent or contain an outbreak.

How You Can Help

About New World Screwworm

New World screwworm (NWS) is a blowfly that is not normally present in the US. Unlike native blowflies, whose larvae (maggots) consume decaying flesh, NWS larvae consume living flesh of warm-blooded animals. NWS blowflies lay their eggs on open wounds (even tick bites) and the umbilicus of newborns of warm-blooded animals. Animals that have recently given birth are also at risk.

Female NWS can lay hundreds of eggs which appear as raft-like clusters of white eggs around the edges of wounds. The maggots which hatch from these eggs then feed on the surrounding living flesh resulting in devastating wounds which can eventually be fatal.

Two images showing maggots inside an open wound and eggs and larvae on the face of a deer.

Left: A female New World screwworm fly lays eggs on an open wound in a Key deer. Right: Eggs and larvae (maggots) below the eye in a Key deer. Photo credit: FWC-FWRI-Fish and Wildlife Health

The lesions are deep and thickened; they are usually draining and have a foul odor. When the larvae mature, they drop from the wound into the soil, pupate, and emerge as adults.

Three images showing a large hole in the neck of a deer and a close up view of the same lesion.

Cross section of NWS lesion in Key deer indicating how thick and deep the lesion can be. Photo credit: FWC-FWRI-Fish and Wildlife Health

The impact of NWS on wildlife and domestic animal health can be severe. When present in 1930s to 1950s it is believed to have significantly reduced Florida’s deer population. The disease would likely reduce fawn survival and potentially kill adult animals. NWS can also infest people.

NWS were eradicated from the United States in the 1960s; however, incursions have occurred including a severe outbreak in 2016 in Key deer in the Florida Keys. Currently NWS flies are found in some Caribbean islands and South and Central America. Since 2023, screwworm flies have been expanding north in several Central American countries, including into northern Mexico. NWS could arrive in Florida via this expansion of range or through the movement of infested animals and people. If introduced into Florida, NWS would be able to reproduce and persist in much of the state due to Florida’s subtropical climate. If established, NWS may take years to eradicate. Control is directed at early detection and limiting the spread.

REPORT MAGGOTS IN LIVE WILDLIFE OR HARVESTED ANIMALS!

Florida Fish and Wildlife Conservation Commission – Wildlife Health

For observations in domestic animals (and wildlife) please contact the Florida Department of Agriculture and Consumer Services

Please immediately report any live or harvested mammals or birds with the following signs: 

  • Wounds or genitalia in recently harvested game animals that contain maggots: Unlike other maggots that feed on dead tissue, screwworms infest fresh, living wounds and burrow deep within the flesh. Wounds may have a foul odor and bloody discharge and are often thickened and deep. NWS should not be confused with nasal bots in deer which are fly larvae normally infesting the nasal sinuses and are commonly seen in healthy harvested deer when removing the head.
  • Irritated or erratic behavior observed or seen on remote camera/video: Infested animals may shake their heads, act lethargic, or isolate themselves from other animals. Also be on the lookout for large draining wounds.

What to do if you see signs of NWS 

Early detection of NWS is critical to prevent or contain an outbreak. 

  • If the animal is harvested, do not move the carcass. Do not field-dress or consume.
  • Wear gloves when handling the carcass and wash well afterwards.
  • Take photos and record the location. Use your phone to take pictures of the wounds or larvae. If possible, record the GPS coordinates of the animal's location. 

Immediately report the finding:

  • Florida Fish and Wildlife Conservation Commission – Wildlife Health
  • For observations in domestic animals please contact the Florida Department of Agriculture and Consumer Services (FDACS). Suspected infestations in wildlife may also be reported to FDACS.

If a good Samaritan calls regarding a live animal with maggots: 

  • Advise that they do not handle or move the animal, and ask them to take photos
  • Get their name and contact information and immediately contact the Florida Fish and Wildlife Conservation Commission (FWC) and the Florida Department of Agriculture and Consumer Services (FDACS) at the numbers listed. 

Upon intake inspect patients for: 

  • Wounds, umbilicus of newborns, genitalia containing maggots: Unlike other maggots that feed on dead tissue, screwworms infest fresh, living wounds and burrow deep within the flesh. Wounds may have a foul odor and bloody discharge and are often thickened and inflamed. NWS should not be confused with bots in the skin of squirrels (commonly seen in late summer/early fall). 

What to do if you see signs of NWS

Early detection of NWS is critical to prevent or contain an outbreak. 

Immediately report the finding:

  • Florida Fish and Wildlife Conservation Commission – Wildlife Health
  • For observations in domestic animals please contact the Florida Department of Agriculture and Consumer Services (FDACS). Suspected infestations in wildlife may also be reported to FDACS.
  • Quarantine the animal and consider euthanasia
  • Take photos – photos of the wound and larvae before treatment.
  • Remove all larvae and eggs and save in isopropyl alcohol
  • Practice good biosecurity. 
  • Ensure all bedding is frozen (although survival of larvae is possible) before double-bagging. Wait for results before disposing.

How you can help – REPORT MAGGOTS IN HARVESTED ANIMALS!

Please immediately report any harvested mammals or birds with the following signs:  

  • Wounds or genitalia in recently harvested game animals that contain maggots: Unlike other maggots that feed on dead tissue, screwworms infest fresh, living wounds and burrow deep within the flesh. Wounds may have a foul odor and bloody discharge and are often thickened and deep. NWS should not be confused with nasal bots in deer which are fly larvae normally infesting the nasal sinuses and are commonly seen in healthy harvested deer when removing the head. 

What to do if you see signs of NWS

Early detection of NWS is critical to prevent or contain an outbreak.

  • Take photos and record the location. Use your phone to take pictures of the wounds or larvae. Obtain precise harvest location from the hunter If possible.
  • Collect maggots in isopropyl alcohol. 
  • Bag and freeze the carcass

Immediately report the finding:

  • Florida Fish and Wildlife Conservation Commission – Wildlife Health
  • For observations in domestic animals please contact the Florida Department of Agriculture and Consumer Services (FDACS). Suspected infestations in wildlife may also be reported to FDACS.

More information

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