The federal government defines an invasive species as a “species that is non-native (or alien) to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health.”
According to the Texas Parks and Wildlife Department, estimates suggest that the annual cost of invasive species in the U.S. is approximately $219 billion.
To date, more than 800 species have invaded Texas, and experts predict the trend will continue to increase, according to the Texas Invasive Species Institute. Existing impacts in Texas are in excess of $1 billion per year.
From creepy and crawly to downright destructive and dangerous, here are a handful of invasive intruders Texans should keep an eye out for:
Black Velvet Leatherleaf Slug
Native origin: South America
The terrestrial slug can grow as long as 3.5 inches in length. As its name suggests, the black velvet leatherleaf slug is typically black and has a velvety, wrinkled mantle, according to the Texas Invasive Species Institute. The slug has two ocular tentacles. The black velvet leatherleaf slug doesn’t closely resemble any native terrestrial slugs, according to the Texas Invasive Species Institute.
The slug poses a threat to humans as it is a known vector of the nematode parasite that causes abdominal angiostrongyliasis in humans.
Initially found in Orange, Texas, the slug’s known distribution has expanded to several of the state’s counties, including Brazoria, Brazos, Caldwell, Chambers, Fort Bend, Galveston, Harris, Liberty, Montgomery, Washington and Wharton counties, according to the Texas Invasive Species Institute.
Giant African Land Snail
Native Origin: East Africa
According to Texas Invasives, Giant African snails found in the United States can be one of three species: giant African snail, giant Ghana tiger snail, and the West African snail. All three species of snails are terrestrial and can grow up to 8 inches in length and 4 inches in diameter. The shells of the snail are darker colored with striped markings. The snails reproduce rapidly and can lay as many as 1,200 eggs annually. With an enormous appetite and an aggressive behavior, the giant African snail is considered of the most damaging snails in the world. The snail poses a health risk to humans and should not be handled as they are known carriers of the parasite which transmits eosinophilic meningitis.
The first known possible sighting of the giant snail in Texas occurred in Houston in 2013.
Native Origin: Europe
Feral hogs are found in every Texas county except El Paso, and generally inhabit the state’s white-tailed deer range, with the highest population densities occurring in east, south and central Texas. Currently, there is an estimated population in excess of 1.5 million feral hogs in Texas. Feral pigs can have detectable influences on wildlife and plant communities as well as domestic crops and livestock. Extensive disturbance of vegetation and soil occurs as a result of their rooting habits. Feral hogs also compete with certain species of wildlife and livestock. Feral hogs are considered an unprotected, exotic non-game species that “may be taken by any means or methods at any time of year,” according to TPWD.
Native Origin: Southeast Asia
The terrestrial flatworm resembles a “hammerhead shark with a rounded head,” according to Texas Invasives. Up to 30 centimeters long, the hammerhead flatworm is typically light colored with several dorsal stripes and a dark-colored collar. Found across the southern U.S., the worm prefers hot, humid environments. They feed and move about during the night, according to Texas Invasives. During the day hammerhead flatworms spend their time out of the sun. They may be found out on the soil, driveways, patios, and sidewalks after heavy rains. The hammerhead flatworm is a known predator of earthworms.
Native Origin: South America
The nutria is a large, dark-colored, semiaquatic rodent that looks like “a beaver without the large flat tail,” according to TPWD. Nutria are generally found from the Rio Grande Texas east to the eastern Texas border, and from Big Bend northeast to the Dallas-Ft. Worth area , often inhabiting marshes, swamps, ponds and lakes, according to Texas Invasives. Extensive disturbance of vegetation and soil can occur as a result of their burrowing habits. Nationally, the estimated average loss of resources caused by nutria likely exceeds $1 million annually, according to Texas Invasives.
Red Imported Fire Ant
Native Origin: South America, specifically Brazil
Red imported fire ants damage electrical wiring and some crops. The mounds can ruin lawns, and more ecologically important, they can displace native ants from their habitat. The red imported fire ant’s presence has led to a reduction in population numbers of all indigenous ants, according to Texas Invasives. Birds, especially those that are ground-nesters such like the bobwhite quail are vulnerable to the ants, which eat newly-hatched chicks and destroy unhatched eggs. The ants attack quickly and in large numbers and their bite stings -- something almost every Texan has had the unfortunate experience of observing at one point or another.
The red imported fire ant is found throughout Texas, especially in the southern and southeastern counties, according to Texas Invasives.
Native origin: Russia
The zebra mussel is a small freshwater mussel. They grow to about 1.5 inches and have a distinctive zebra-striped shell -- hence, the name. A single zebra mussel can produce up to one million microscopic larvae, according to Texas Invasives. The microscopic larvae can’t be seen with the naked eye and can survive for days in water trapped on boats. “Once zebra mussels become established in a water body, they are impossible to eradicate with the technology currently available,” according to the online National Atlas of the United States. Texas boaters in public fresh water are required to drain all water from boats before leaving or approaching a body of water. The first Texas infestation was found in Lake Texoma in 2009, according to the Texas Parks and Wildlife Department.
Currently, Zebra mussels are found in lakes and rivers in six Texas river basins -- the Red, Trinity, Brazos, Colorado, Guadalupe, and San Antonio rivers. Twenty- seven Texas lakes are classified as fully infested with zebra mussels -- meaning “the water body has an established, reproducing population,” according to the Texas Parks and Wildlife Department. : Austin, Belton, Bridgeport, Brownwood, Buchanan, Canyon, Dean Gilbert (a 45-acre Community Fishing Lake in Sherman), Eagle Mountain, Georgetown, Granger, Grapevine, Inks, Lady Bird, Lewisville, Livingston, Lyndon B. Johnson, Marble Falls, Medina, O.H. Ivie, Pflugerville, Placid, Randell (local Denison access only), Ray Roberts, Richland Chambers, Stillhouse Hollow, Texoma, and Travis.
Native origin: Indo-pacific
Lionfish are reddish brown and white striped fish that have large fins with venomous spines.
The species has no known predators other than humans. A single female lionfish is able to lay about two million eggs annually. The lionfish is the fastest growing coastal invasive, according to Texas Invasives.
“Lionfish are able to eat prey up to half their body length and utilize hunting strategies such as hunting in groups, herding prey fish with their long pectoral fins, and flushing hidden organisms out of the sediments,” according to the TPWD. “This, combined with their ability for rapid reproduction and lack of predators throughout their invasive range, allows them to quickly populate habitats and adversely affect native reef fishes and invertebrates.”
Lionfish are a type of reef fish, which generally prefer to live near hard structures like oil rigs, wrecks, coral reefs, and jetties, according to the Texas Parks and Wildlife Department.
Native origin: Central and South America
Several species of invasive armored catfishes are found in Texas. Armored catfishes can range in size from three inches to over three feet and feed on algae. Armored catfishes superficially resemble catfish, but do not have the barbels (tentacle-like projections growing from the mouth) distinctive of catfish. Unlike catfish, armored catfish have dark-colored lines and markings and scaly-textured skin.
Established, reproducing populations of armored catfishes have been observed in the San Antonio River, Comal Springs, San Marcos River, and San Felipe Creek as well as in the bayou and canal systems in the Houston area, according to Texas Invasives.
“With the over-abundance of loricariids in freshwater ecosystems, local indigenous species can be out-competed and reduced,” according to Texas Invasives. “This could lead to a collapse of freshwater fisheries in addition to the obvious ecological dangers.”
Sources: Texas Invasives, Texas Parks and Wildlife Department