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 rapidly expanding 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 

over 6 million and distributed across more 

than 35 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, 

sign, 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 Issued October 2016

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.