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 (Apis mellifera) was introduced from England in 1622. The Virginia Company loaded a ship with species common in England which colonists could farm, part of the attempt by the London Company investors to broaden the economy of the colony beyond tobacco. The ship brought cages of rabbits (connies), which already existed in Virginia in the wild, to provide a new source of domesticated livestock. The investors wrote to the colony:¹

We have by this ship and the Discovery [another ship] sent you divers sorte of seed, and fruit trees, as also Pidgeons, connies, Peacock maistives [mastiffs], and Beehives, as you shall by the Invoice perceive; the preservation and increase whereof we recommend unto you.

The new, introduced honeybees swarmed naturally and spread widely. They were kept by the colonists in traditional "skeps," and harvesting the wax and honey required destroying the hive. Lorenzo Langstroth did not invent the modern beehive until 1851, finally allowing beekeepers to maintain a hive while removing the wax and honey.

Virginia colonists raised honeybees in traditional "skeps;" the modern hive was not invented until 1851
Sources: Wikipedia, Bee Skep and geograph, Bee skeps at St Fagans

In 1622 Native Americans were already familiar with the multitudes of biting insects in North America; introduction of the honeybee was of minor concern to them. There were already multiple bee species in North American, and even species of "stingless bees" that produced honey collected by the Mayans. A Puritan pastor named John Eliot claimed in the mid-1600's that the Native Americans had so unfamiliar with honeybees that there was no Algonquian language name for them, so honeybees were supposedly called "white man's flies."

That claim may have been manufactured, but it has been a long-lasting story. A British officer noted during the American Revolution:²

...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, aggressive 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.

fire ants have arrived in Virginia
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

The arrival of non-native fire ants has triggered an evolutionary change in eastern fence lizards (Sceloporus undulatus). The immune systems of lizards have more antibodies that neutralize the venom toxins of the ants, a change with may be associated with adults consuming fire ants as a new food source.

Adult lizards typically respond to threats by lying flat and trying to blend in with the landscape. That passive behavior allows fire ant scouts to recruit others and inject enough venom with their stingers to kill a lizard. Where the ranges of eastern fence lizards and fire ants overlap, the lizard population has developed longer legs. Longer legs are useful in flicking off the scout ants and avoiding a lethal attack, but it breaks the camouflage used by lizards to hide from other predators.³

non-native fire ants have triggered evolutionary changes in eastern fence lizards (Sceloporus undulatus)
Source: Judy Gallagher, Eastern Fence Lizard - Sceloporus undulatus, Meadowood SRMA, Mason Neck, Virginia

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 between 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 successful 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 identified to date to control the population of non-native catfish is to encourage recreational anglers to catch them and to support a commercial fishery.⁴

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 (Tsuga canadensis and T. caroliniana) are at risk of being extirpated in Virginia by the invasive hemlock woolly adelgid (Adelges tsugae). In its flightless form, the aphid literally sucks the juices out of the tree. The mass of adelgids in white, wooly nests underneath hemlock branches slowly divert the nutrients in the tree's xylem ray parenchyma cells, starving the tree.

The adelgids reproduce asexually on hemlock trees and create two forms of young. One form remains feeding on the hemlock, while the other transforms into a tiny winged fly. In their native Japan, the winged flies would land on a Tiger tail spruce tree (Picea torano) and reproduce sexually there. The Japanese hemlocks and spruce have evolved adequate resistance to withstand the damage cause by the feeding of the hemlock woolly adelgids,

Picea torano is not present naturally in North America, so the winged adults in Virginia all die. However, enough asexual reproduction occurs for the adelgids to stay continuously on a hemlock tree in Virginia until it dies.⁵

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)

the hemlock woolly adelgid inserts a tube into the hemlock tree's needle and extracts nutrients from the xylem ray parenchyma cells
Source: US Forest Service, Biology and Control of Hemlock Woolly Adelgid (Figures 10 and 12)

in Virginia, Tsuga canadensis and T. caroliniana are at risk of extirpation because of the hemlock woolly adelgid
Source: US Forest Service, Biology and Control of Hemlock Woolly Adelgid (Figure 3)

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, and Sitka deer at Assateague Island.

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

Wildlife agencies claimed in 2022 to have successfully eradicated nutria (Myocastor coypus) from the eastern side of the Chesapeake Bay. Nutria had been introduced to the Delmarva area in the 1940's, raised for fur and meat. Escaped and released nutria had no natural enemies in the bay and nutria bred three times a year, so the population soon exploded in the wild.

The muskrat-like nutria damage natural marshes by eating not just the top of vegetation, but also digging out the roots and stems. At Blackwater National Wildlife Refuge, 5,000 acres of marsh were transformed into open water or "a field that's been hit by a rototiller." As a consequence, the population of marsh-dependent species dropped precipitously.

Eradication involved trapping 14,000 nutria between 2002-2015. After most nutria were trapped, the remainder were found by capturing a few, placing tracking collars on them, and finding the remainder of the population when the gregarious animals gathered together.

The nutria removal project cost $30 million, and is still not completely successful. Because nutria are still present on the western side of the Chesapeake Bay in Tidewater Virginia marshes, biologists constantly monitor the marshes on the eastern side of the bay to prevent a reintroduction.

The manager of the Blackwater National Wildlife Refuge noted the value of removing all the nutria in order to protect the marshes:⁶

Once the grasses are gone, the marshes disappear, and then so do all the species living there.

nutria have been eradicated from the eastern side of the Chesapeake Bay, but some still remain in Virginia's Tidewater marshes
Source: US Fish and Wildlife Service, Nutria

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:⁷

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.⁸

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 larvae in New Orleans, Norfolk, or perhaps New York, since the crab's natural range is from the Gulf of Mexico 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:⁹

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 treated 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.¹⁰