Wildlife Monitoring and Management for New World Screwworm
Authors: Marcus E. Blum1, James C. Cathey2, Roel R. Lopez3, Parr Rosson 4, Sarah Fuller 5, Hunter Reed6, Kory Gann 7
Texas is home to more than 100 mammal species and over 600 bird species that may be particularly vulnerable to the impacts of New World screwworm infestations. The following information provides both urban and rural Texans with the knowledge needed to monitor, detect, and report signs of NWS infestations to help protect wildlife.
Introduction
The New World screwworm (NWS), Cochliomyia hominivorax, is a parasitic fly that lays its eggs in or near wounds and the mucous membranes of living mammals and birds. After hatching, the larvae burrow into the wounds and feed on live tissue—a condition known as myiasis. These wounds can result in rapid health decline and death, especially in free-ranging wildlife that do not receive veterinary care and cannot be closely monitored like livestock.
Texas is home to more than 100 mammal species that may be at an especially high risk, including more than 5 million white-tailed deer. In addition to ecological and aesthetic value, native wildlife are a key contributor to the state economy. A 2023 study by the Texas A&M Natural Resources Institute found that the management and hunting of white-tailed deer alone contributes more than $9 billion to the Texas economy every year.
The following information provides both urban and rural Texans with the knowledge needed to monitor, detect, and report signs of NWS infestations to help protect wildlife ranging from squirrels and coyotes to white-tailed deer, mule deer, black bear, and wild turkey.
What to look for
- Open sores and tissue damage found on living, warm-blooded wildlife
- Wounds as small as a tick bite can become infested.
- Maggots may be visible in wounds.
- Areas commonly infested include the head and neck, as well as the umbilical area of newborn mammals.
- Mucous membranes with wounds, including genitalia, eyes, nose, mouth, and ears, are also highly susceptible if wounds are present on these tissues. Fresh wounds where antlers shed from the skull, as well as antlers damaged while in velvet, are also susceptible to infestation.
- Foul odor like rotting flesh
- Strange behavior in wildlife
- Head shaking
- Discomfort and irritated behavior
- Lethargy and isolation from other animals
Do NOT attempt to approach any wildlife closer than a reasonable viewing distance — no closer than 25 yards. Captive wildlife, including those in zoological facilities, may also be at risk.
What to do if you suspect New World screwworm in wildlife
Immediately report any sightings of live animals with maggots
to your local Texas Parks and Wildlife Department biologist. Texas A&M AgriLife Extension Service county agents and AgriLife Extension specialists can serve as key contacts to help connect you with proper resources and official reporting agencies.
- REPORTING IS CRITICAL to implement management actions to curtail the spread of NWS. Texans are advised to report any suspected sightings of infested animals.
- Comply with any movement and treatment requirements that may be implemented for animals by state and federal agencies.
- If housing captive wildlife, contact local TPWD biologists.
- For suspected infestations in exotic hoofstock, contact the TAHC or your local veterinarian for treatment options.
For wildlife biologist assistance:
Texas Parks and Wildlife Department (TPWD)
512-389-4505
For livestock:
Wildlife monitoring considerations
- Monitoring wild, free-ranging animal populations is considerably more difficult than monitoring domestic or confined animals.
- If possible, monitor animals every few days for signs of NWS.
- This may be more feasible for wildlife held at rehabilitation and zoo facilities.
- Monitoring free-ranging wildlife will pose challenges; however, increased monitoring will assist state and federal agencies in responding to new outbreaks.
- Monitor current movement patterns and behavior pre-outbreak so abnormalities in behavior, movement, and location will be more apparent should infestations of NWS occur in your area. It is suggested that daily observation records be kept to better track animal behavior.
- Susceptibility to New World screwworm infestation varies by sex and season because of behavioral changes that increase the likelihood of injury in animals. Seasonal management practices among confined wildlife, such as ear tagging, de-antlering, and capture can also increase the potential risk for infestation.
Infestation potential varies based on seasonal behavioral changes
Female Wildlife and Young
Birthing Season
Birthing season places females and their young at risk for infection. New World screwworm can lay eggs on mucous membranes, such as the genitalia, experiencing a wound. The umbilical region of newborn animals is also highly susceptible to infestation.
High mortality of females and offspring have the potential to severely reduce populations of large mammals such as white-tailed deer, mule deer, bighorn sheep, pronghorn, black bears, exotic wildlife and other mammal species.
Male Wildlife
Breeding Season
Breeding seasons see male wildlife competing for mating dominance. Fighting styles vary among species, so rates of wounds may differ. Deer species may be more prone to open wounds from fights than species like bighorn sheep. Mature males had the highest mortality rates in Key deer during the 2016 New World screwworm epidemic that occurred during rut.
Antler Growth
Male deer species will have higher rates of infection during velvet shedding, antler shedding and antler growth.
Wildlife monitoring techniques
Trail cameras
Trail cameras can be useful tools in identifying wildlife displaying clinical signs consistent with NWS infestation. Place trail cameras at locations where wildlife frequent, such as water and food sources, along trails, and at potential crossings.
When placing a trail camera, attach it to a sturdy tree or post overlooking an area potentially frequented by wildlife. Place the camera roughly 2 to 3 feet high (roughly knee high) off the ground and approximately 15 feet from the target area where you think the animals will frequent. Finally, consider the orientation of the camera in relation to sunrise and sunset. It is recommended to orient the camera to face north to minimize false triggers and low-quality photos caused by shadows and sun rays.
Hunting stands, blinds and wildlife viewing areas
These areas provide opportunities to survey animals via optics such as binoculars or scopes. High-quality optics will increase your ability to identify potentially infected animals quickly and with a higher degree of accuracy.
Taking notes from your hunting stand can assist you in tracking your wildlife populations over time. Keep track of the number of bucks, does, fawns, and unidentified individuals you see at each stand. Note the dates and times you make these observations. Using this data, TPWD wildlife biologists can calculate herd composition
Backyard and urban wildlife watching
Many wildlife species are drawn to residential areas and the resources they offer, such as food, cover, shelter, and water. Monitoring wildlife that may frequent residential areas, such as deer, squirrels, raccoons, and coyotes, is a meaningful step to aid in early detection in urban and suburban areas. Use tools such as binoculars and security recording systems to ensure you maintain a safe distance from the animals.
Pay attention to signs of scavengers, such as vultures and coyotes. If you see vultures circling on your property, investigate what is attracting them.
Certified wildlife rehabilitators
Animals that have been identified as in need of rehabilitation should be thoroughly inspected for signs of NWS. Citizens should not move or surrender animals to wildlife rehabilitators that exhibit any signs of infestation. Immediately contact your local TPWD wildlife biologist if those signs are present. Unsupervised movement will spread larvae and the NWS infestation.
If a wildlife rehabilitator receives an animal exhibiting signs of NWS infestation, they should immediately contact their local TPWD wildlife biologist.
In most cases, wildlife biologists advise people not to interfere with or remove wildlife they believe may be orphaned.
Wildlife management
TPWD is the state agency responsible for managing the natural and cultural resources of Texas, including wildlife. Consult your local TPWD wildlife biologist for management recommendations specific to your property.
Your local TPWD wildlife biologist can assist you with methods for monitoring wildlife populations and, if warranted, harvest recommendations on your property through their Technical Guidance and Managed Lands Deer programs. Population monitoring and recordkeeping are critical for adaptive management strategies if NWS impacts wildlife populations on your property. Keep detailed records so you can measure changes in populations. If changes are noticed, contact TPWD for assistance.
Key demographic information to monitor includes abundance, fawn-to-doe ratios, and buck-to-doe ratios. Record observations of bucks, does, fawns, and unidentified (e.g., could not determine sex or age class) deer to develop abundance and various ratios. If possible, also collect age class data to help determine which age classes are being impacted by NWS.
Please immediately isolate suspected animals and report instances of New World screwworm as follows:
- Livestock: Texas Animal Health Commission
- Wildlife: Texas Parks and Wildlife
- Small animals: Your local veterinarian
Please send news and media inquiries to [email protected].
1Assistant Professor and Extension Wildlife Specialist, Department of Rangeland, Wildlife and Fisheries Management, Texas A&M College of Agriculture and Life Sciences, Texas A&M AgriLife
2Professor and Associate Director, Texas A&M Natural Resources Institute, Texas A&M University, Texas A&M AgriLife
3Department Head and Director, Department of Rangeland, Wildlife and Fisheries Management, Texas A&M Natural Resources Institute, Texas A&M College of Agriculture and Life Sciences, Texas A&M AgriLife
4Professor and Associate Department Head for Extension, Department of Rangeland, Wildlife and Fisheries Management, Texas A&M College of Agriculture and Life Sciences, Texas A&M AgriLife
5Natural Resources Communications Coordinator, Department of Rangeland, Wildlife and Fisheries
6Wildlife Veterinarian, Texas Parks and Wildlife Department
7Big Game Program Director, Texas Parks and Wildlife Department
