Invasive Species in Virginia

Source: Virginia Department of Wildlife Resources, Snakehead Fish in Virginia

Native species are those that "belong" here. In normal use, that means the species were in Virginia before the arrival of the Europeans. Sailors from various nations visited the coastline of Virginia in the 1500's, and the Spanish landed a party in 1570, but the settlement of Jamestown in 1607 is often considered the reference point for "native" and "non-native" species.

It helps to remember that the Native Americans imported crops into what became Virginia - tobacco, corn, beans, and squash in particular - before the Europeans arrived.

The balance of nature in the state of Virginia has been tilted by non-native species. Some were brought here; cows, horses, honeybees, pigs, potatoes, and most other agriculturally-valuable species are not native to Virginia. Even the species of tobacco that we grow is not native. The honeybee was introduced from England to Boston, then escaped and spread widely. A British officer noted during the American Revolution:¹

...the bee is not natural to America, for the first planters never observed a single one in the immense tract of woods they cleared, and what I think stands forth a most indubitable proof that it is not the Indians, as they have a word in their language for all animals, natives of the country, have no word for a bee, and therefore they call them by the name of the Englishman's Fly.

Other species hitchhiked here uninvited, including Japanese honeysuckle and the veined rapa whelk. Red imported fire ants (Solenopsis invicta) reach the Gulf Coast states from South America first, then expanded their range over several decades. Fire ants, aggresive invertebrates with a venomous sting, feed on the young of ground nesting birds and are a painful nuisance to animals, dogs, cattle, and other animals. Their mounds are a headache for farmers.

The invasive species reached Hampton Roads in 1989. A quarantine by the Virginia Department of Agriculture and Consumer Services did not stop the fire ants from expanding north to Petersburg and west into Halifax County by 2022, with light infestations in Martinsville and Lee County.

Ant-killing baits are not authorized in farm fields or pastures, in order to keep the chemicals out of the food supply for humans. Outside the quarantine area, state personnel will try to destroy fire ant mounds. Within the boundaries of the quarantine area, landowners are welcome to control the ants but the state will no longer invest the effort.

The range of the fire ant is limited by cold weather. They are likely to infest the Eastern Shore and much of Tidewater and part of Southside Virginia, but not become common in the Shenandoah Valley or Northern Virginia.²

snakehead fish expanded their known range between 2004-2015, reaching the Rappahannock River
Source: Virginia Tech College of Agriculture and Life Sciences, Currently Known Distribution of Red Imported Fire Ant in Virginia (April 2022)

with a warmer climate, fire ants can expand further into Virginia
Source: US Department of Agriculture, Suitable Habitat for Imported Fire Ant Colonization Under Natural Rainfall and Irrigated Conditions

Aquatic organisms are hard to see unless you're a waterman, but can involve great expense. The zebra mussel was extirpated from Millbrook Quarry upstream of Lake Manassas, but companies with intake pipes drawing water from the freshwater rivers still fear they will have to spend heavily to keep their intake/discharge pipes clear of obstruction.

snakehead fish expanded their known range between 2004-2015, reaching the Rappahannock River
Source: Virginia Department of Game and Inland Fisheries, Mapping Where Snakehead Fish Are Found in Virginia

The flathead catfish (Pylodictis olivaris) is native to drainages in Texas and the Mississippi River watershed. That species was stocked in the James River beween 1965-1970 to increase recreational fishing opportunities, and has become an established invasive species.

Blue catfish (Ictalurus furcatus) are native in the Mississippi, Missouri and Ohio rivers. They were stocked in the Rappahannock, James, and Mattaponi rivers in the 1970's. The assumption that the higher salinity in the Chesapeake Bay would block them from spreading was wrong, and they have invaded the Potomac and other rivers throughout the Chesapeake Bay.

Their appetite for blue crabs and other fish has disrupted the food web; some blue catfish grow five feet long and weigh over 100 pounds. As extraordinarily sucessful apex predators, blue catfish are threatening the populations of other species. Other than osprey and bald eagles, the catfish have few natural predators. Blue catfish may compose as much as 75% of the total fish biomass in the James and Rappahannock now.

Virginia and Maryland have established an Invasive Catfish Task Force, working with Federal agencies, academics, and non-government stakeholders. The best strategy identifie to date to control the popuulation of non-native catfish is to encourage recreational anglers to catch them and to support a commercial fishery.³

electrofishing in the James River allows biologists to estimate the population of blue catfish
Source: Flickr, Monitoring invasive blue catfish in the James River (Chesapeake Bay Program)

Hemlock trees are at risk of being extirpated in Virginia by the invasive hemlock woolly adelgid (Adelges tsugae). The aphid literally sucks the juices out of the tree, diverting the nutrients in the tree's phloem from the needles. The natural predators in Asia keep the hemlock woolly adelgid in check, but those predators are not in Virginia to provide a check of the population growth of the aphids.

non-native insects which arrive without normal predators, such as the hemlock woolly adelgid, can threaten the continued existence of native species
Source: Integration and Application Network, University of Maryland Center for Environmental Science, Dead Eastern Hemlock trees in Shenandoah National Park, Virginia (by Alexandra Fries)

Some of our most common plants and animals are not native. That "English sparrow" pecking away at the crumbs outside McDonalds, the starlings feeding in a flock at the edge of an open field, the Japanese honeysuckle vine climbing along the fenceline, the blue flowers of chicory along sidewalks - none of them are native to Virginia. They are aliens, imports from outside the state.

chicory (Cichorium intybus), native to Europe, is now naturalized and thrives in disturbed sunny spots throughout Virginia

Does that make them lesser species, some form of life to value less? Perhaps, but not necessarily.

The Clematis growing wild at Aquia Landing park in Stafford County smells wonderful - but it's a non-native species. The native version is an equally-pretty climbing vine with a white flower, but it lacks the perfume of the non-native species. The hydrilla that is expanding along the bed of the Potomac may clog the channels into marinas. Still, it's clearly serving the function of submerged aquatic vegetation, trapping silt and providing a place for invertebrates to grow.

Some non-native species spread beyond where they are planted, but are minimally invasive. Daffodils and periwinkle are indicators of old homesteads, but do not spread wildly into nearby habitats.

daffodils are not a native species, but rarely expand beyond where they were planted

Some non-natives are harmful, however. Purple loosestrife and Phragmites spread throughout Virginia wetlands, displacing native species that the animals have used as food sources. The non-native species, while large and "showy," do not provide the same food value to the animals in the area.

The native critters are unfamiliar with the non-native plants, and do not utilize their biomass effectively. Plants and animals that have evolved together create a web of life which adapts gradually to change. As a result, the exotics - in these two cases, invasive species that spread rapidly - reduce the health of the native animals in the wetlands.

Other non-native species in Virginia include carp, coyotes, feral pigs at Back Bay National Wildlife Refuge, mute swans in the Chesapeake Bay, nutria, and Sitka deer at Assateague Island.

Source: Virginia Department of Conservation and Recreation, Virginia Invasive Species Council

The most recent invasive species is the spotted lanternfly (Lycorma delicatula). The spotted lanternfly is from China, and its primary food is the "tree of heaven" (Ailanthus altissima) from the same area. However, it damages grape vines, hops, fruit trees, and other plants. By sucking out plant juices and facilitating the growth of sooty mold, the species threatens major agricultural products in Virginia.

The first sighting of spotted lanternflies was at a stoneyard near Winchester in 2018. The site was being monitored because the pest had been found first in 2014 at a stone importing business in Pennsylvania, and it regularly shipped products to the Winchester site.

Egg masses as well as dead adults were found on ailanthus trees in Winchester rather than in a shipment of stone, indicating the species had become established at one site in Virginia. Using the authority in the Virginia Tree and Crop Pests Law, the Virginia Department of Agriculture and Consumer Services imposed a quarantine for Frederick County and the city of Winchester on May 28, 2019.

Businesses were required to complete training to spot the invasive pest, and to obtain a permit to ship outside the quarantine zone any articles that were considered a risk for lanternfly dispersal. Those articles included lumber, stone, stone, shipping containers, outdoor household articles such as grills, and recreational vehicles. Virginia officials did not go so far as to create inspection stations on I-81, however.

Lanternflies are poor fliers, traveling just short distances. A state official said:⁴

The artificial spread is what we're trying to contain here... We can't really contain the natural spread. If a bug decides to fly somewhere, there's not much we can do about it.

spotted lanternfly
Source: Animal and Plant Health Inspection Service (APHIS), Spotted Lanternfly Photo Gallery

Natural range extensions will occur as the climate changes. Alligators, currently found in North Carolina, could naturally occupy Dismal Swamp and the Northwest River/North Landing River in southeast Virginia as winter temperatures rise.

There are nine native species of lizards in Virginia. The pattern of sightings of three additional species of lizards reveals they were introduced via the pet trade, sold as chameleons, and hitch-hiked on plants. The Mediterranean house gecko is now common in urban areas, while Italian well lizards arrived in Northern Virginia after 2010. By 2020, juveniles of the green anole lizard were being found in Virginia Beach. That non-native species was able to adapt and start breeding.⁵

Virginia has exported invasive species, as well as become host to them. A blue crab population became established in the Mediterranean Sea in 2012, presumably transported as larvae in a ship's ballast water. The ship could have acquired the larvea in New Orleans, Norfolk, or perhaps New York, since the crab's natural range is from the Gulf of Nexico to New England.

There were no natural predators in the Mediterranean for blue crabs. They displaced native species, as well as fouled European fishing nets. Officials in Ireland became alarmed in 2021, when a dead blue crab was discovered on an Irish beach. An official at the National Biodiversity Data Centre in Waterford, Ireland, commented:⁶

It's definitely not a species we want to see becoming established in Ireland

blue crabs are native from the Gulf of Mexico to New England, bur are an invasive species in Europe
Source: Flickr, Callinectes sapidus (blue crab) (Cayo Costa Island, Florida, USA) 1 (by James St. John)

In Puget Sound, populations of cordgrass (Spartina alterniflora) are reated as an invasive species which the State of Washington's Department of Agriculture will eradicate. The state's Noxious Weed Control Board has identified cattails as a noxious weed to be eliminated.⁷