Pet Vet to the Rescue - Screw Worms

By Christine Newman, DMV, for The Montgomery News | August 18, 2026

New Jersey-based veterinarians recently received an e-mail alert regarding the New World Screwworm. This fly had been eradicated from the United States in 1966. But, it's back.

A screw worm fly.

Photo from US Department of Agriculture

On June 3, the USDA announced screwworm larvae were found in a calf in Texas. Since then, 41 cases have been reported, primarily in livestock but including one dog. Any warm-blooded animal including livestock, birds, pets, and humans may be affected. Should we in New Jersey be concerned?

The New World Screwworm (NWS) fly is unusual. The larvae feed on living tissue as opposed to the necrotic tissue most flies prefer. Eggs are laid in openings in the skin or on mucous membranes. One fly can lay as many as 3,000 eggs in a single wound or body opening.

The eggs hatch into larvae and feed on living flesh for about six days then drop to the ground, burrow, and pupate into flies. The entire life cycle takes 21 days.

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The fly is attracted to blood. Even a small puncture wound or tick bite can provide an appropriate site to lay eggs. The larvae burrow deep under the skin and may eventually burrow into body cavities. According to Dr. Theresa Kelliher, “A quarter-inch wound on Day 1 can become a five-inch wound on Day 2.”

Untreated wounds can be fatal. The first known case in a dog was found in a shih tzu in Texas who presented to the veterinarian for two small wounds near his eye. Although the wounds were small, there was an unpleasant odor raising the veterinarian’s suspicion for a deeper issue.

The patient was sedated, the wound explored, and 40 larvae, later identified as NWS larvae, were removed. The dog was treated with NexGard to kill any remaining larvae.

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New Jersey has implemented travel restrictions for all animals coming from affected areas to our state. The NJ Division of Consumer Affairs e-mail states:

“The risk to New Jerseyans from New World Screwworm is very low. But public health means acting before a threat arrives, not after.” It seems unlikely our pets will encounter NWS, but anyone traveling to Texas or New Mexico with pets should exercise caution.

The FDA approved preventative/ treatment medications for dogs and cats, including: Credelio, Credelio CAT, NexGard and NexGard Combo. The USDA website includes up-to-date data about number of cases, species involved, and the geographic location. Control measures include releasing sterile flies, trapping flies, and strict surveillance and reporting measures.