FERAL SWINE: Impacts on Threatened and Endangered Species

What Are Feral Swine?

Feral swine (also called wild pigs, boar, 

feral hogs, and many others) are a 

destructive, invasive species. They vary 

in color from black to brown and even 

patchwork colors, and range in size from 

75 to 250 pounds. Feral swine belong to 

the family Suidae and were introduced 

into the United States in the 1500s by 

early explorers and settlers as a source 

of food. Over centuries, domestic pigs, 

Eurasian boar, and their hybrids have 

escaped, been released, and been 

reintroduced, setting the scene for the 

expanded populations we have today.

Feral swine directly impact threatened and endangered species by preying on the nests, 

eggs, and young of ground-nesting birds and reptiles. They actively hunt and consume 

small mammals, reptiles, amphibians, and insects. They compete for important resources 

such as food, water, and habitat, often displacing other wildlife. Additionally, wildlife are 

vulnerable to many of the diseases and parasites feral swine carry. The most far-reaching 

impact feral swine have on native wildlife is habitat change and destruction through 

their rooting, wallowing, trampling, and feeding behaviors. Feral swine are ecosystem 

engineers, which means they can change their environment by altering water quality 

and runoff in wetlands, shifting plant composition and distribution in grasslands, and 

decreasing tree diversity in forests. Feral swine have played a role in the decline of 

nearly 300 native plants and animals in the United States; over 250 of these species are 

threatened or endangered.

Invasive species are defined as plants 

or animals that are non-native to an 

ecosystem and often have broad 

negative impacts on the environment 

into which they are introduced. With 

feral swine populations of approximately 

6 million and distributed across more 

than 31 States, the damage they cause 

is significant to the environment, 

economy, and human health. Feral 

swine damage to habitats, predation 

on wildlife, and disease transmission 

can be linked to the decline of nearly 

300 native plants and animals in the 

United States, many of which are 

threatened or endangered species. 

Why Are They Considered an Invasive Species? 

What Is Their Impact? 

Animal and Plant Health Inspection Service

Feral swine cause problems by damaging native ecosystems, preying on or 

competing with native wildlife, and spreading diseases.

• Do not relocate feral swine to new areas or transport them to other States.

• Share the knowledge; discourage transportation and spread of feral swine. 

• If you live in a State with no or low levels of feral swine, report any 

sightings, signs, or damage to wildlife or agriculture officials in your State.

What Can I Do?
Sea Turtle

Feral swine’s keen sense of smell, 

along with their digging and 

rooting abilities, allows them to 

prey on reptile eggs buried in 

sand or soil. On Keewaydin Island in Florida, in some years, feral 

swine nest predation devastated endangered green sea turtle 

reproduction by destroying every nest on the island. The turtles’ 

nest success improved dramatically after feral swine were removed.

Prairie Chicken 

Lesser prairie chickens are a 

unique and iconic species. Prairie 

chickens nest on the ground, 

leaving their eggs and young easily 

accessible. Their decline can be partially attributed to predation 

by feral swine. Habitat damage is also a threat to lesser prairie 

chickens. Feral swine will root up and consume native plants and 

introduce invasive plant seeds to the freshly disturbed soil, thereby 

accelerating the spread of invasive grasses and weeds. 

 

Houston Toad 

Feral swine are aggressive 

animals that live in groups, called 

sounders. They will actively 

chase off other species with their 

aggressive behavior, particularly around feeding or wallowing 

areas. Feral swine wallowing in seasonal pools in parts of Texas 

have prevented the endangered Houston toad from breeding 

successfully by disturbing adult toads, eating eggs, and 

contaminating water. After fencing was installed, toads were 

able to successfully breed because swine were excluded from 

damaging their breeding habitat.

Mead’s Milkweed

Feral swine degrade the tallgrass 

prairie and glade habitat that 

the milkweed depends on for its 

lifecycle. They also prey on this 

milkweed by uprooting it and consuming the roots and seed pods. 

This delicate plant takes 15 years or longer to reach sexual maturity, 

making it very sensitive to feral swine damage. Mead’s milkweed is 

important for many other species, including the Monarch butterfly, 

American bumblebee, digger bees, and other pollinators. 

Hine’s Emerald

Dragonfly

The Hine’s emerald dragonfly is 

extremely rare, only living in a 

few small populations in Illinois, 

Michigan, Missouri, and Wisconsin. 

Feral swine threaten this unique species by damaging the 

delicate wetland habitat it depends on through rooting and 

wallowing. Dragonflies are important parts of an ecosystem 

because they prey on mosquitoes, gnats, and biting flies and 

their larva provide food for fish.

Hawaiian Moorhen 

Known as the “keeper of fire” in 

Hawaiian tradition, the Hawaiian 

moorhen is threatened by feral swine 

through direct predation on ground nests and habitat damage. 

Feral swine root up and consume vegetation on hillsides, causing 

erosion and flooding downstream in the wetlands the Hawaiian 

moorhen uses for breeding and nesting. Flooding of their shoreline 

nests is the most common reason for nest loss, followed closely by 

nest predation. 

Examples of THREATENED and ENDANGERED SPECIES 

at Risk From Feral Swine Impacts and Damages

USDA is an equal opportunity provider, employer, and lender. Photo credits: Images courtesy of USDA-APHIS Wildlife Services and U.S. Fish and Wildlife Service. 

Program Aid No. 2195f Revised May 2020

Want To Learn More?

Call Wildlife Services, a program within the U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection 

Service, at 1-866-4-USDA-WS or visit www.aphis.usda.gov/wildlife-damage/stopferalswine to learn more about the 

problems caused by this invasive animal, as well as to seek advice and assistance in dealing with feral swine.