There are now more than 300 invasive species of animals and plants in Pennsylvania. These species have been documented by state authorities.
The most dangerous invasive species in Pennsylvania may be subject to public management techniques.
Table of Contents
Invasive Animals of Pennsylvania
Here are some of the most common types of invasive animals in the state of Pennsylvania.
1. Balsam Woolly Adelgid
Small adelgids of this family are found at a higher elevation, typically on grand fir, silver fir, and other types of coniferous trees.
The species (Adelges piceae) is now widespread around the state. While some types of fir trees can survive their invasion, other species such as Fraser fir don’t have any adaptations to allow them to fight off this woolly adelgid.
The non-native status of Balsam Woolly Adelgid means fir might not survive its invasion.
Damages can be so significant that the species can deteriorate even in large areas of Fraser fir in the state.
Some Fraser firs in national parks of the US have already been killed almost completely by this quick-spread invasive species.
2. Brown Marmorated Stinkbug
This species of brown shield-shaped bug (Halyomorpha halys) is one of the most important fruits and vegetable pests in the state.
Brown Marmorated Stinkbugs are some of the species that create necrotic areas on fruits and legumes, making them unfit for stores.
Hazelnut plantations have also been impacted by this species across the world.
As a major pest, Brown Marmorated Stinkbug needs management techniques, especially from May to June, the period that marks its peak activity.
This is also a species that can fly indoors as a nuisance pest.
Bugs of this family have few natural predators. The Samurai Wasp is one of the species with a growing use against the Brown Marmorated Stinkbug in the United States.
3. Elongate Hemlock Scale
Another very common pest in the state that impacts fir species is the Elongate Hemlock Scale (Fiorinia externa).
This species first established itself on the underside of needles and not on the top side of needles as the male Elongate Hemlock Scales do in other states.
Yellow fir needles are a sign this is a serious invasion.
Even small invasions can be problematic as tens of these small bugs can place themselves on each needle.
Killing local fir populations is one of their direct impact results. These bugs are also known to limit exports as trees carrying the invasive species cannot live in the country.
4. Emerald Ash Borer
Emerald Ash Borers (Agrilus planipennis) are believed to have an Asian origin. They first spread to Europe and then to North America.
This is a species that bores deep in ash trees, moving under tree bark and eventually killing trees.
If left undiscovered, this species kills even the largest ash trees within a few years.
The borer has a metallic green color and its presence requires immediate attention.
Removing the infested tree or putting a given area of ash trees into quarantine is among the recommended management techniques to prevent large-scale invasions.
Insecticides and other treatments are also routinely used against these bugs. Treatments under tree bark as also getting common.
5. Introduced Pine Sawfly
A pine tree that’s defoliated on top in the state might have been impacted by The Introduced Pine Sawfly (Diprion similis).
This is a species that impacts pine trees across multiple generations. The first generation of its caterpillars feeds on old needles while the following generations feed on both new and old needles.
A selective capacity to which needles are eaten makes regeneration almost impossible.
Once all the needles are eaten, at least those in the upper half of the tree, these caterpillars turn to the bark for food.
Eventually, the tree dies. An infested pine tree can die within a few years, depending on its age.
6. Japanese Beetle
You can identify Japanese Beetles (Popillia japonica) by their green and brown coloring with a metallic quality to their colors.
This is a species that overwinters in the ground as larvae and emerges in the spring eating grasses, squash, legumes, and fruits.
The beetle may be the most common type of invasive bug on lawns around the state.
Its emerged larvae and adult beetles start feeding on grass roots early in the season. Much of their damage goes unnoticed at first as they live in the ground.
The species has widespread Northeastern US distribution reaching Pennsylvania from its initial area of introduction in New Jersey.
7. Spongy Moth
According to different researchers, Spongy Moths (Lymantria dispar) or Gypsy Moths are one of the world’s most invasive species.
The rapid spread and a wide range of hosts make this moth and its caterpillars highly dangerous to Pennsylvania trees.
A range of hardwood trees such as oak and softwood tree such as fir are the hosts of the species.
The hairy caterpillar with a red stripe has always the risk of defoliation.
Adults are identified by their contrasting colors between the sexes.
Female Spongy Moths have a white color while males are tan and dark brown.
Oak, aspen, and apple, are some of the most impacted species of this moth, together with cypress.
8. Spotted-wing Drosophila
This bee-resembling insect (Drosophila suzukii) is one of the most invasive species of fruits in Pennsylvania.
It has been first discovered in California and on The West Coast but it has since spread to Eastern parts of the country as well.
This is a species that eats raspberries, strawberries, and many other types of berries. It can be found in gardens but its impact is on crops or commercial-scale fruit production units.
Luckily, Spotted-wing Drosophila is a species that can be controlled through natural measures.
Even on a large scale, water and vinegar traps prove fatal for the fly. You can add buckets of a mixture of water and vinegar around fruits. This acts as bait that drowns the invasive species.
9. Grass Carp
These dangerous species (Ctenopharyngodon idella) were imported to different areas of the world to control aquatic vegetation.
Grass Carp in the US has been introduced from Taiwan but it now hurts the ecosystem.
It competes with local fish for food and it’s often more successful and more aggressive in feeding behavior.
This species is not allowed to be introduced in ponds, lakes, and rivers of the state anymore. Fishermen mays still try to catch it as it often puts up a good fight once hooked.
10. New Zealand Mudsnail
New Zealand mudsnails (Potamopyrgus antipodarum) are present around some of the largest bodies of water in the state.
This species has contrasting impacts depending on its region. It typically lacks an invasive status in many of the countries it lives in.
This is due to a known list of parasite species that control its numbers.
Parasites such as flukes aren’t present in the state which means the mudsnails can feed on and attach themselves to different immersed mechanisms in water.
Furthermore, New Zealand Mudnsials reproduce asexually which means they don’t need to mate to multiply.
11. Northern Snakehead
Northern Snakehead fish (Channa argus) has an elongated cylindrical shape and they are found across multiple US states despite efforts to eliminate them.
This is a species with very long teeth as an adult. As a predator, it eats and eliminates many juvenile fish of other local species.
Even young Northern Snakehead fish are known for their high zooplankton.
Preventive measures include the illegal import status of the species.
Fishermen are also instructed not to release Northern Snakehead once caught, regardless of its size or age.
12. Quagga Mussel
Quagga Mussels (Dreissena bugensis) are an introduced species of European origin.
These mussels are responsible for a diminishing water oxygen level. They reduce oxygen in their habitat to the extent that other species are impacted.
Furthermore, the Quagga Mussel is also known for eliminating algae that serve as food for local species.
These mussels may be eaten but they tend to absorb many toxins in the environment being considerably less healthy than other more common edible mussels.
13. Red Swamp Crayfish
Red Swamp Crayfish (Procambarus clarkii) is one of the most common types of crayfish found in fish stores.
This is one of the species which faces high competition with Chinese crawfish.
In Pennsylvania, it has an invasive status due to its aggressive nature as it competes for food with local crayfish.
This species has a dark red color with bright red spots and long claws.
You can distinguish the species from other red, brown, or dark red species of crayfish by its front claws covered in bright red spots on small bumps.
14. Round Goby
Round Goby fish (Neogobius melanostomus) are excellent feeders and predators.
Both diurnal and nocturnal, these fish place themselves in slow-moving areas of the water waiting for prey.
A high aggressiveness towards food, locations, and nesting areas compared to native species makes it invasive.
Round Goby often drive out local fish species from their nesting locations.
Sculpin is one of the species Round Goby has a considerable impact on.
At the same time, this small fish has started to attract the attention of local predators who may see it as a feeding option.
Bass and large trout may see invasive Round Goby as food and eventually stop their considerable spread.
15. Rusty Crayfish
Rusty Crayfish (Faxonius rusticus) is one of the most common invasive species of crayfish in Northeastern US states, including Pennsylvania.
This is an aggressive species often fighting for food with local non-aggressive species of crayfish.
Rusty Crayfish is also larger than local species. This means fewer predators are willing to take on the species.
As a result, it always grows in number driving out local species of crayfish and fish.
This fish can be picked by hand and cooked. Its large size recommends the species for human use.
16. Zebra Mussel
A common sight in Lake Erie, Zebra Mussel (Dreissena polymorpha) is now a considerable problem in the Northwestern parts of the state.
This is a species of invasive filter feeder that reduces the amount of invertebrate food local species feed on.
It also attaches itself to boats and canal walls, posing a problem for communication channels.
This species is also believed to spread disease.
A type of bird-killing botulism has been associated with these mussels.
Most native species in Lake Erie that share the same habitat as Zebra Mussels are now almost completely extinct.
17. Asiatic Clam
This species (Corbicula fluminea) also has an Asian origin. It has spread to most parts of the world with intense boat activity.
Ships brought it to the area of The Great Lakes.
A high multiplication rate is one of the reasons Asiatic Clams outcompete local species for food.
Asiatic Clams also take considerably less to reach sexual maturity. This species also shows higher adaptability to live in less-than-ideal lakes and rivers.
A self-fertilizing species, Asiatic Clam may live less than the local clam but it also multiplies considerably faster than local species.
18. Common Carp
A large type of fish, Common Carp (Cyprinus carpio) shop an invasive behavior outside its native regions.
Now established in areas of North America, this is a species with a diverse diet which makes it a more adaptable species compared to many local fish.
Common Carp feed on crustaceans at the bottom of the lake.
Crayfish of various sizes are also part of its diet. This fish may also eat different types of fish remains on bottom sediments.
Worms and the eggs of other species are also eaten by Common Carp.
Since it also eats aquatic plants and since it has a high appetite, this is a species with a considerable invasive risk status associated with its name.
It has even been named one of the 100 most dangerous invasive species in the world due to its destructive nature in its introduced habitats.
Alewife (Alosa pseudoharengus) is one of the most common invasive species in The Great Lakes. It can be found in higher numbers in Lake Michigan as opposed to Lake Erie.
This species has also gone past its peak population a few decades ago.
It remains a reason for concern, mainly through the elimination of local zooplankton species.
Biological control methods have been put in place since the ‘70s, with varying degrees of success.
Some of the natural predators of the species (such as trout) have also gone through a near-extinction process which allowed Alewife to multiply considerably.
20. Allegheny Crayfish
One of the smallest types of invasive crayfish in the state is Allegheny Crayfish (Faxonius obscurus).
This is one of the smallest types of live bait used in fishing.
Allegheny Crayfish are often found in areas where other invasive species such as Rusty Crayfish live.
Its reduced size means the Rusty Crayfish often manages to establish itself to the detriment of the Allegheny Crayfish.
Found on the bottom rocky areas of lakes and rivers, this type of crayfish also shows lesser adaptability to polluted areas compared to Rusty Crayfish.
21. Sea Lamprey
Often referred to as an eel, the predatory and invasive Sea Lamprey (Petromyzon marinus) is one of the reasons local fish species in The Great Lakes are nearly extinct.
Lake trout and like whitefish are a couple of species that have seen parasitic behavior of Sea Lamprey in the state.
This species attaches itself to a host and drinks its blood, essentially killing it.
One of the reasons it had such a great impact here was due to its feeding habits which included lake trout.
This is a type of trout that previously had no real threats in the area of The Great Lakes.
22. European Starling
European Starling (Sturnus vulgaris) has both beneficial and detrimental roles across the state.
A capacity to eat some of the most common bug and insect pests in the state has been linked to possible benefits the species has on the ecosystem.
However, it also outcompetes local species such as woodpeckers for food.
This is a species that shows an almost omnivorous diet and higher habitat adaptability.
Unlike other small birds, it can live and share its habitat with humans. This means it can eat fruit, legumes, seeds, and even leftovers from the garbage.
23. House Sparrow
One of the most common types of invasive small birds in the state is House Sparrows (Passer domesticus).
These are birds that live in cities and villages, together with humans.
High adaptability, an endless list of feeding options as a true omnivore, and a reduced number of predators make this species invasive.
Domestic cats are among the most common types of predators of the species.
House Sparrows have owls and hawks as their most dangerous predators, but neither of these predators shares its urban living preferences.
Accidental introduction to these parts of the continent is credited with its appearance in the state. However, House Sparrow populations are declining in many of its typical habitats.
24. Mute Swan
Mute Swans (Cygnus olor) are often admired on lakes. However, they have an invasive role around The Great Lakes.
A diminishing of aquatic plants and local birds has been linked to Mute Swans.
This is a species that drives waterfowl out with its aggressive feeding behavior.
A similar invasive status has also been linked to other countries where the Mute Swan was introduced.
Unlike in other countries, Mute Swans double their populations within a decade in the area of The Great Lakes due to a high multiplication rate and a low number of natural predators.
25. Wild Boar
Wild Boars (Sus scrofa) are one of the most numerous invasive mammals in the state and North America.
Nobody knows exactly how many wild boars there are in the state but it’s estimated more than a few million wild boars live in the United States.
This species erodes the soil in its path. It destroys crops and pastures.
It may also eat all types of legumes it finds on farms and crops.
Forests and forest floors are also often impacted by wild boars. Their destructive habit is known all across the state.
Wild boards aren’t regulated for hunting in Pennsylvania which means a simple hunting license allows you to go out and hunt for the invasive species.
26. Rustic Jumping Worm
Rustic Jumping Worms (Amynthas agrestis) are an invasive species that outcompetes local worm species.
They hurt the ecosystem as well as they eat leaf litter considerably more than any other local species.
This creates ecosystem imbalances which may change the natural plant and worm diversity of their soils.
Rustic Jumping Worms are controlled by various means which don’t require chemicals.
For example, farmers burn leaf litter through a controlled process.
This enriches the soil and it also stops the spread of Rustic Jumping Worms.
Invasive Plants of Pennsylvania
Plants can be just as invasive as animals, hurting the local ecosystem.
27. Eurasian Watermilfoil
This aquatic species (Myriophyllum spicatum) has now invaded much of The Great Lakes.
A submerged species, the Eurasian Watermilfoil spreads quickly. It initially reduced oxygen levels but it even crowds large fish which have insufficient space in their habitat.
Clogged canals and pathways also result from the widespread distribution of the Eurasian Watermilfoil.
This species is now managed through multiple chemical-based and biological control agents.
The introduced Eurasian Watermilfoil weevil is among the bugs that exclusively eat the aquatic plant.
Other invasive species such as Grass Carp also excessively feed on the Eurasian Watermilfoil.
28. Japanese Knotweed
One of the most common invasive plants in the state is the medium to tall Japanese Knotweed (Fallopia japonica).
This is a species that invades riparian areas. These habitats near water are often overgrown by plant which has deep roots and stops other plants from growing next to the water.
This plant can be seen close to rivers and streams. It has also spread its habitat to canals and around ditches.
While most plants of this species grow up to 5 feet, the plant can become very tall measuring up to 10 feet if left unmanaged.
29. Giant Knotweed
Giant Knotweed (Fallopia sachalinensis) is an even larger species with a similar Asian origin.
Like Japanese Knotweed, Giant Knotweed also likes to live in riparian areas. It grows along lakes, streams, and rivers.
It becomes highly invasive with mechanical management techniques such as cutting.
This weed sprouts back faster and more vigorously when cut. Removing it completely is also difficult as it grows deep roots.
Chemical control methods with pesticides are recommended in areas where these chemicals don’t reach the water.
This management technique is always more successful in the spring, as opposed to late summer pesticide control.
30. Hybrid Knotweed
Hybrid Knotweed (Fallopia X bohemica) easily grows to a height of up to 10 feet in a few years.
This is a species adapted to riparian areas but has also established itself along roads, with seed dispersion.
It features large green leaves and small off-white flowers.
State residents aren’t required to cut it on their property in most municipalities.
The weed quickly overgrows its area and it spreads by also killing all other smaller plants in its path with its roots and by blocking direct sunlight.
This species used to be seedless in the state, as all of the plants were males. Today, Hybrid Knotweed also comes with seeds which means it has rapid dispersal.
31. Autumn Olive
This plant (Elaeagnus umbellata) is known for its dark green leaves and round red fruits.
It disperses itself quickly and it requires management techniques to eliminate from the garden.
Initially introduced as a decorative species, this shrub eventually became invasive as it overgrew its area and it inhibited other plant growth.
You may cut it down so that you clear it from your property but Autumn Olive also needs pesticide spraying so that it doesn’t sprout back.
32. Common Reed
Common Reed (Phragmites australis) is one of the most common invasive species in brackish water, shallow water, and marshes.
This species may also grow to a size of up to 7-10 feet if left unmanaged.
Most areas with Common Reed only show tall plants as these aren’t inhabited areas.
A common sight in the area of The Great Lakes, Common Reed is almost impossible to remove due to its deep roots.
This species also creates vast areas of monocultures along water sources. No other small to medium-sized plant can grow in its established area.
These columnar green invasive species (Hydrilla verticillata) grow in the water. Submerged, this is a species that quickly overgrows a habitat.
Hydrilla has been known to clog canals and waterways for boats.
Temporary solutions include mechanical management by cutting the weeds for boat passage.
Clippings are spread out by boats to different areas. Herbicide is sometimes used against the plant, but it also doesn’t stop it from growing back in the future.
This type of invasive plant (Persicaria perfoliata) is known for its multiple barbs.
Wearing gloves is among the few methods which allow you to pull it out when it grows in your garden.
Pesticides are alternative options to keep it away. You may still need to spray pesticides over the plant and its roots as some roots may remain in the ground when pulled out and resprout.
The seeds of this plant may also survive in water, even for up to a few days.
35. Japanese Barberry
Japanese Barberry (Berberis thunbergii) is a species with green leaves and red fruits. Its leaves also turn red in the fall.
Spreading by seed, Japanese Barberry is widespread in Northern US states.
Selling its seeds is now prohibited in many parts of the country as it can change the nitrogen levels in the soil.
Deer are known to control multiple weeds, but they tend to stay away from Japanese Barberry.
Furthermore, this plant retains high moisture which favors the spread of ticks.
36. Purple Loosestrife
Purple Loosestrife invasive plants (Lythrum salicaria) resemble asters and lavender.
A known flowering plant, Purple Loosestrife is seen as a colorful plant in pots and an invasive species in gardens.
It creates overgrows in its area as its seeds are spread by pollinators.
Purple Loosestrife is a species further known for its monotypical habitat creation. Fields of Purple Loosestrife also attract other pollinators such as butterflies and moths.
37. Black Swallow-Wort
Black Swallow-Wort (Vincetoxicum nigrum) is one of the common species of small to medium-sized invasive plants with red fruits.
It grows to a maximum height of 6 feet while many of its plants are 4-5 feet tall.
Black Swallow-Wort grows next to woodlands. It can also be found on grasslands where it overgrows fields of native species.
It impacts various species of bugs and insects which feed on local plants such as Monarch butterflies.
38. Multiflora Rose
Multiflora Rose (Rosa multiflora) was initially introduced as a decorative tall plant in North America.
This species grows to a maximum size of up to 16 feet which makes it one of the tallest invasive species in Pennsylvania.
Once established, this plant might be too expensive to remove as it often needs excavation.
This is a species that vigorously sprouts back when cut.
39. Pale Swallow-Wort
This species (Vincetoxicum rossicum) is found in the Northern parts of the state. It grows to a vigorous tall size with green leaves, green stems, and dark red flowers.
Pale Swallow-Wort inhibits the growth of many local plants.
Unlike other invasive species, Pale Swallow-Wort shows a preference for living close to poison ivy.
40. Oriental Bittersweet
This type of plant (Celastrus orbiculatus) has been introduced to North America from Asia.
It has a decorative role but it became an invasive plant as it kills all other plants it grows around.
Originally from East Asia, this species prefers areas with plenty of sunlight which means it doesn’t grow next to woodlands.
As it grows tall, Oriental Bittersweet also outgrows shorter local plants that die without sufficient natural sunlight.
41. Common Frogbit
Common Frogbit (Hydrocharis morsus-ranae) are aquatic plants seen in slow-moving bodies of water such as lakes and ponds.
This green species has white and yellow flowers.
Common Frogbit are either male or female. Females make seeds while males make pollen.
This species tends to multiply rapidly, changing the local flora and stopping natural light penetration in water.
Common Frogbits can grow so dense they stop boats from easily navigating waters.
42. Lesser Celandine
The damp ground next to water is one of the preferred habitats of the Lesser Celandine (Ficaria verna).
This is a species known for its large yellow flowers.
Lesser Celandine is a highly toxic invasive species. Unlike other plants, it tends to be highly toxic to humans if ingested.
Livestock is always at risk as animals are more likely to eat dangerous amounts of these toxic plants.
Its toxins can even kill large animals such as cattle.
Winberry (Rubus phoenicolasius) grows in the wild across Pennsylvania.
This is a European-origin species that is often confused with different types of berry-producing plants.
Its fruits are edible and are seen in red color when ripe.
Moist soils are preferred by Wineberry. This is an invasive species as it proves difficult to control.
Cutting the plant only prompts its sprouting back quicker and denser.
The only true method of eliminating Wineberry is to dig it out, even multiple times until none of its roots remain behind.
44. Morrow’s Honeysuckle
This type of honeysuckle (Lonicera morrowii) is less fragrant than its alternative used for cosmetics.
It has been introduced as a decorative species in North America.
The problem with Morrow’s Honeysuckle is that its thickets shade out local herbs and small plants.
Local plants die without sufficient sunlight.
The good news is Morrow’s Honeysuckle can be pulled out. You can use your hands to pull it out of the ground if spotted in your garden.
Early pulling is recommended as smaller plants have shallow roots. Herbicides can also be used in wider areas covered in Morrow’s Honeysuckle.
45. Tartarian Honeysuckle
Tartarian Honeysuckle (Lonicera tatarica) is a large type of invasive honeysuckle that can grow to a height of 10 feet.
This is a species that grows in large shrubs, killing all other plants in its areas.
Small orange fruits are produced by the Tartarian Honeysuckle.
While not truly poisonous, these fruits should not be eaten by humans or animals. Those accidentally eating these fruits can experience diarrhea and an upset stomach.
46. Japanese Stiltgrass
This is a type of introduced dense grass in North America.
Japenese Stiltgrass (Microstegium vimineum) tends to grow vigorously and taller than local grass. It overcrowds local fauna.
Unlike other invasive species, Japanese Stiltgrass grows in multiple types of habitats as it shows adaptation to low light conditions.
As a result, this type of grass can quickly cover forest floors, changing the natural ecosystem in an area where local grass rarely grows.
Early management measures are recommended as this grass can be laborious to take out within 1-2 years once established in a new area.
47. Amur Honeysuckle
Amur Honeysuckle (Lonicera maackii) is one of the most studied types of invasive honeysuckle in Pennsylvania.
This is a species that prevents native plants from growing back once it establishes their roots.
A thicket quickly kills local plants and herbs.
Armur Honeysuckle provides nutrition for local birds such as robins.
It’s believed the nutritional value of the plant is considerably reduced as opposed to the higher value of local plants it kills for various species of birds.
Kudzu (Pueraria lobata) is one of the most commonly introduced plants around the world.
This is a species used for property limits as well as a climbing perennial plant to decorate homes and fences.
Kudzu is also a heavy plant that can come with structural risks on hold homes or traditional wooden sheds that it overgrows.
A very high growth rate of tens of feet per year makes this species a risk to local plants which it overgrows and kills.
Kudzu can grow on some of the tallest shrubs in the state. It can also grow on trees which means it’s a matter of time until even the largest trees are overgrown.
This invasive species also impacts cattle and wild animals in the state. It covers pastures at ground level as well.
This means cattle have a difficult time finding suitable feeding grasses.
49. Garlic Mustard
Garlic Mustard (Alliaria petiolata) is one of the rapidly spread invasive species starting to be seen in multiple areas of the state.
This species is only invasive due to its quick emergence.
Garlic Mustard tends to emerge in early spring, earlier than almost all other local plants.
It used this timing to its advantage as it grows taller than small local plants and herbs. By the end of the spring, it might be too late for local plants which are outgrown.
Without access to light, smaller plants emerging later in the season are killed by Garlic Mustard.
This is a process that tends to become more destructive with time. Climate change shows Garlic Mustard is more adaptable than local plants.
50. Japanese Honeysuckle
This type of honeysuckle (Lonicera japonica) grows in a wide range of habitats and it may also grow next to fences, trees, and other large plants.
It kills smaller vegetation in its path by growing taller and emerging faster in the season.
Known for its yellow flowers, Japanese Honeysuckle multiplies by seeds.
Japanese Honeysuckle is only truly invasive in certain conditions, such as in areas with full sun exposure.
It’s here that it creates thickets that kill local species as the plant struggles to reach its maximum size when grown in partial shade.
Birds carry their seeds for rapid dispersal.
Pesticides are used against this species in extreme control measures. 1-2 sprayings are required each year to control the areas already overgrown.
These plants can also be removed by hand when found in gardens or when they’re small enough to have shallow roots.