By Kirsten Vernin, Senior Research Assistant in Watershed Quality
Every year, HARC supports National Invasive Species Week, an annual campaign that aims to raise awareness about invasive species, the threats they pose, and what can be done to prevent their spread. Feral hogs are one such invasive species that can be found in 35 states, with an estimated U.S. population of over six million.[1] Nearly half of these hogs are in Texas.
Pigs are not native to North America. They were first introduced in the 1500s by Europeans as a food source. Eurasian wild boars (Sus scrofa) were later released for recreational hunting in the early 1900s. Today’s feral hog populations are now comprised of escaped domestic pigs (Sus scrofa domesticus), Eurasian wild boars, and hybrids of the two.[2] Their population continues to rapidly grow because of their high reproduction rate, diet, and a lack of natural predators.[3]
Texas is home to an estimated 2.6 million feral hogs, which, as noted above, is nearly half of the U.S. population of the species.[4] El Paso County (the western most county in Texas bordering New Mexico and Mexico) is the only county that has not reported any feral hog sightings.[5]
So, what makes them invasive? According to research done by Texas A&M University and the National Wildlife Research Center, feral hogs cause damage to the tune of $500 million a year in Texas,[6] and the monetary losses due to crop damage are estimated to be $1.5 billion a year in the U.S.[7] Those are huge numbers, and so is their ecological impact.
Feral hogs damage agricultural lands and the environment by impacting water quality and destroying crops and native habitats. They disturb the ground and vegetation along wetlands and bayous when they forage or wallow, increasing particles, sediment, and dirt in the water, which changes its acidity and oxygen levels, resulting in unfavorable living conditions for native plant and animal species within the stream. This dirt and sediment can also block sunlight from reaching aquatic life and plants that rely on it to survive.
Feral hogs do not have sweat glands, so they usually search for wetlands and bayous to keep cool during hot and humid Texan summers. Since they spend their time in and around bodies of water, their waste also ends up in bayous, either directly through the deposition of fecal matter, or indirectly through stormwater runoff, which increases concentrations of bacteria in surface waters. In fact, a recent study in Alabama showed that streams in watersheds with feral hogs had 40 times the bacteria levels than those in watersheds without them.[8] This has the potential to be detrimental to our water quality in Texas, causing human health concerns.
Perhaps the most concerning potential damage is that feral hogs can spread diseases to humans. They have been known to carry brucellosis,[9] a bacterial disease that spreads among pigs through close contact. Infected pigs carry these bacteria for life. Humans can become sick if blood, body fluid, or tissues from an infected animal comes in contact with the human’s eyes, nose, mouth, or cuts to their skin. This disease can cause severe, long-lasting health problems, and even death, if it is not diagnosed and treated quickly.
How can this problem be managed? There are many different strategies and tools for managing feral hog populations, including hunting, trapping, and excluding individual hogs from areas using non-lethal tools such as fencing. Most wildlife professionals use lethal methods to remove feral hogs from an area, such as shooting and trapping, as these are often more effective strategies than exclusion alone.
Large corral traps are one of the most effective ways of removing larger numbers of feral hogs because of the trap’s ability to capture an entire sounder (another name for a group of wild hogs). When only trying to catch one or two feral hogs, a box trap or snare can be solid options, but snaring increases the risk of capturing nontarget native wildlife or domestic animals. Aerial shooting from helicopters is another highly effective strategy if done by experienced personnel on properties without dense groundcover where the animals can hide. New research by Texas A&M AgriLife Extension Service is also investigating the use of a warfarin-based toxicant as another management tool.[10] Bait with warfarin was placed in specially designed feeders that prevent access by non-target species like cattle and deer. Feral hogs were conditioned to access the bait before the poison was applied. Once added, the hogs consumed lethal doses within five days of consistent access to the bait. If used appropriately, correctly, and consistently, warfarin-based toxicant could be another useful tool to manage hogs in the future.
Wild hog control in Texas and throughout the U.S. is a collaborative effort between many governmental and private entities with expertise in specific areas of control, management, and damage mitigation. The Texas Cooperative Wildlife Services program is a joint effort between USDA-Animal and Plant Health Inspection Service (APHIS)-Wildlife Services, the Texas A&M AgriLife Extension Service, and the Texas Wildlife Damage Management Association, whose mission is to protect the state’s resources from damage caused by impactful species.[11] The number of feral hogs removed from the state through this program has increased since 2019, with 51,215 hogs removed in 2021.
As part of the Double Bayou Watershed Protection Plan, HARC, along with its project partners, is focused on improving the water quality of this area which spans Liberty and Chambers counties. Removing feral hogs in this area is especially important because removals have been shown to markedly improve water quality. In Texas, a reduction in bacteria levels was achieved when the Texas Wildlife Services removed 537 feral hogs from the Plum Creek Watershed in Caldwell and Hays Counties over a two-year period. After the feral hogs were removed, the overall level of bacteria in Plum Creek decreased by 48% when compared with an adjacent area where feral hogs were still present in high numbers.[12] [13]
Most people use a mix of tools and management options to effectively manage the number of feral hogs found on their property. Unfortunately, there is no silver bullet, and the complete eradication of feral hogs is extremely difficult to achieve. However, it is important that we collectively engage in combating the spread of feral hogs, manage their population in Texas, and limit the damage they cause.
To learn more about how to lessen the spread of this invasive species and how to manage a feral hog problem on private property, check out these useful Texan resources:
[1] https://www.aphis.usda.gov/aphis/ourfocus/wildlifedamage/operational-activities/feral-swine/sa-fs-history
[2] https://tpwd.texas.gov/huntwild/wild/nuisance/feral_hogs/
[3] Ibid.
[4] Ibid.
[5] https://www.aphis.usda.gov/wildlife_damage/feral_swine/images/2022-feral-swine-population-map.jpg
[6] https://agrilife.org/txwildlifeservices/files/2022/10/State-report-FY21.pdf
[7] The Quiet Invasion (galvbayinvasives.org)
[8] Bolds, S.A.et al. 2021. “Impacts of a Large Invasive Mammal on Water Quality in Riparian Ecosystems.” Journal of Environmental Quality. 50 (2): 441–53.
[9] https://www.cdc.gov/brucellosis/pdf/feral-swine-brochure.pdf
[10] https://agrilifetoday.tamu.edu/2023/08/31/toxicant/
[11] TWS (2021) Texas Wildlife Services State Report FY21. Available at: https://agrilife.org/txwildlifeservices/files/2022/10/State-report-FY21.pdf
[12] Timmons, J. et al. (2011) Feral Hogs and Water Quality in Plum Creek. Texas AgriLife Extension Service. Available at: https://feralhogs.tamu.edu/files/2011/08/Feral-Hogs-and-Water-Quality-in-Plum-Creek.pdf
[13] Texas A&M AgriLife Extension (2010). Feral Hog Project Accomplishments. Available at: FERAL HOG PROJECT ACCOMPLISHMENTS (tamu.edu)
