You may have seen New World screwworm (NWS) in the news, as it was recently detected in the United States for the first time in decades. But what exactly is this parasite, and should you be worried about your dog’s safety? 

New World screwworm is a fly whose larvae feed on living tissue in warm-blooded animals, including dogs. Female flies lay eggs in open wounds or around orifices, like ears or the mouth. Even a small wound, like a scratch or tick bite, can result in an infestation. The larvae that hatch begin to feed on the animal and can cause serious damage.

Information about New World screwworm will continue to evolve as public health officials and veterinarians monitor the situation. In the mean time, a little education can help you understand what to look for and when you may need to reach out to a veterinarian. 

Understanding New World Screwworm

New World screwworm (NWS) was eradicated decades ago in the US, Mexico, and most of Central America.¹ Unfortunately, it has recently been detected in the U.S. again, prompting renewed attention and the need for surveillance in the US.

Although as of August 2026, NWS has only been detected in Texas and New Mexico, dog parents should know the signs and follow current guidance from public health officials and veterinarians.

How Infestation Happens

New World screwworm (Cochliomyia hominivorax) gets its name from the screw-like appearance of the larval (maggot) stage of the fly. The life cycle of the New World screwworm fly requires a live animal to feed on.

Adult female flies are attracted to odors from open wounds or lesions, which can be anything from a tiny scratch to a tick bite or post-surgical wound. They’re also attracted to warm mucous membranes and natural odors emitted from the body's orifices, like the nose and ears. 

The female fly lays multiple batches of eggs around the edge of the wound or orifice. Approximately 12 to 24 hours later, the larvae hatch from the eggs and feed on the animal's living tissue. As the larvae feed, they create screw-like holes that quickly expand the wound. They continue feeding for approximately seven days before maturing. The larvae then exit the wound and drop to the soil to pupate. About six to eight days later, an adult fly emerges.²

The life cycle explains why early care is so important: an infestation can progress from eggs to tissue damage in a short time.

Environmental Needs

NWS activity is temperature-dependent, peaking during warmer months in spring, summer, and early fall. The ideal environment for survival and activity of NWS is between 77-86°F. Average temperatures below ~48°F (9°C) prevent NWS survival.³

Peak New World screwworm fly activity coincides with peak flea and tick season. This is a concern because just the presence of tick bites or scratching flea bites can leave wounds that attract these egg-laying flies. Be sure to ask your veterinarian which year-round flea and tick control plan is right for your dog.

What Are the Signs of New World Screwworm in Dogs?

The earliest signs may be easy to miss. Monitor dogs for signs like irritation, head shaking, foul odor, and for the presence of eggs or maggots around wounds or the ears, nose, mouth, or genitals. A wound that worsens quickly over hours or days needs prompt veterinary attention.

Possible new world screwworm symptoms include:¹

• Small, white egg clusters in or around wounds
• Visible larvae/maggots in or around wounds or orifices 
• Foul odor from wounds or orifices
• Bloody discharge, or clear/pale yellow, watery fluid from the wound
• Wounds that get bigger or deeper over time
• Expanding or “pitted” tissue damage
• Unusual swelling
• Escalating pain
• Persistent licking or scratching
• Lethargy
• Fever
• Reduced appetite
• Irritability
• Isolating from people or other pets

If you notice any of these signs, contact your veterinarian immediately, especially if your dog lives in or recently traveled through an area with reported activity. Do not wait for every sign to appear.

Characteristics of the New World Screwworm Fly

Since the process starts with adult flies laying eggs in open wounds, it’s helpful to know to what the flies look like – especially if your dog currently has any wounds.

Characteristics of adult flies include:

• Similar in size to, or slightly larger than, common house flies
• Metallic blue or green body
• Orange eyes
• Three dark stripes along the back

Fly appearance alone can’t confirm an infestation. A veterinarian and diagnostic laboratory must evaluate suspected cases.

New World Screwworm Treatment for Dogs

If you suspect your dog has NWS eggs or a larval infestation (where the eggs have already hatched), do not attempt to aggressively flush or remove the larvae or eggs at home. This could push them deeper and worsen the damage. Leave the treatment and management of the infection to your veterinarian.

Before You Head to the Veterinary Clinic

It’s crucial that you inform your veterinary clinic that you are concerned your dog may have a New World screwworm larvae infestation before you arrive. This protects other patients and helps the veterinary team manage a suspected case safely.

Tell your veterinarian:

• When you first noticed the wound
• How you think the wound occurred
• How the wound has changed
• Any signs you’ve noticed, including pain, discharge, odor, licking, or changes in appetite or activity
• Where your dog has traveled recently

The Veterinary Exam

Your veterinarian will assess the wound and your dog’s overall health. 

They may recommend testing, such as a bacterial culture of the wound. If they suspect New World screwworm, they will collect samples from the wound to submit for testing.

Treatment and Follow-Up 

Because infestation can be very painful, sedation may be necessary to manually remove larvae, safely clean deep wounds, and remove unhealthy tissue.

Your dog may need antibiotics, pain medications, and supportive care, such as intravenous fluids. Effective oral medications to kill the screwworm larvae are available. Your veterinarian will choose a product based on available FDA-authorized options.

The wound must be monitored closely for healing and possible reinfestation. Follow all discharge instructions closely and keep all follow-up appointments with your veterinarian. New World screwworm larvae treatment may require more than one check as the wound heals.

Your veterinarian will work with state animal health officials and USDA veterinarians to ensure standard treatment procedures are followed. This also helps agricultural leaders keep track of New World screwworm in your area, to help prevent more animals from being affected.  

Traveling with Your Dog Amid New World Screwworm Concerns

Keep a log of your pet’s travel (and any wounds) to share with your veterinarian if you suspect NWS. If you’re traveling with your pet from an active U.S. infested zone, you may be required to follow specific guidance and/or obtain a certification of veterinary inspection. Be sure to check with USDA and state guidance and your veterinarian for import rules prior to travel.. Be sure to check your local state import rules at USDA APHIS State-to-State Pet Travel. 

When arriving or returning with your dog from international destinations, you should always check CDC and USDA guidelines.

Protecting Your Dog if NWS Spikes Near You 

Vigilance beats panic when working to protect your dog from New World screwworm. 

• Use year-round parasite prevention. If your dog isn’t already on one, speak to your veterinarian about the best option. 
• Treat wounds promptly. Clean, protect, and monitor wounds each day according to your veterinarian’s advice.
• Check your dog daily. Look from nose to tail, including the ears, eyes, nose, mouth, armpits, groin, tail base, and spaces between the toes.
• Help prevent wounds. Avoid thorny brush, supervise rough play, keep nails trimmed, and make sure collars and harnesses don’t chafe.
• Check after outdoor activity. Look for wounds after hiking, hunting, rough play, or time in brush. Check crates, fences, and outdoor areas for sharp objects.

Where To Find Current New World Screwworm Information 

Information about New World screwworm will continue to evolve as officials and veterinarians monitor the situation. Use reliable sources to check for updates:

• Screwworm.gov Unified Response Hub
• CDC Situation Summary
• USDA Confirmed Detections Dashboard

Although the risk of New World screwworm is low for most dogs, it's helpful to know what to look for and have a plan. Keep checking your dog after outdoor activities, watch for even small wounds, and contact your veterinarian if something changes. Prompt wound care, smart prevention, and a quick call to your vet are the best forms of protection from New World screwworm.