Pike CNHI - Pennsylvania Natural Heritage Program

Invasive Animal Species
In additional to invasive plants, Pennsylvania is now home to several exotic species of animals including
mammals, birds, fish, and reptiles. These species directly threaten populations of native animals through direct
competition or predation. Other invasive exotic animals can alter habitats and ecosystems by changing plant
cover or diversity. Some of these invasive animals, such as the Norway rat (Rattus norvegicus), are all too
common encounters in our homes and developed areas.
One of the most significant threats to the biodiversity of
Pike County from an invasive animal species is the
hemlock woolly adelgid (Adelges tsugae). This is a
small aphid-like insect that feeds on the leaves of
eastern hemlock trees (Tsuga canadensis). Infestations
of the woolly adelgid appear as whitish fluffy clumps of
feeding adults and eggs along the underside of the
branch tips of the hemlock. This species is native to
Japan and China and was introduced accidentally to
North America around 1924 (McClure 2001). It is
currently distributed from Maine to Georgia and can be
found in over two-thirds of the counties in Pennsylvania
(PA DCNR 2007).
Hemlock decline and mortality typically occur within four to ten years of initial infestation. The adelgid can
cause up to 90 percent mortality in eastern hemlocks, which are important for shading trout streams,
controlling erosion of steep stream banks, and providing habitat for about 90 species of birds and mammals.
This species has the potential to drastically alter the Pennsylvania landscape. Several control options are
currently being tested, but a cost-effective treatment has not yet been found.
The landscape of Pennsylvania was drastically altered by chestnut blight (Cryphonectria parasitica), a fungus
probably introduced to North America from infected nursery stock from China in the 1890s. First detected in
New York City in 1904, it had all but wiped out the American chestnut (Castanea dentata) from Maine to
Alabama. American chestnut once comprised one-fourth to one-half of eastern U.S. forests, and was prized as a
food for humans, livestock, and wildlife and for its durable wood. Today, only stump sprouts from infected trees
remain and the resulting canopy gaps have been filled by the chestnut’s associate species, including oaks and
hickories.
The gypsy moth (Lymantria dispar) has caused extensive defoliation of forests in the northeast. This
European moth was intentionally introduced to the U.S. in 1869 as part of a failed commercial silk production
venture. Its main impact is that it defoliates trees, particularly oak species. This defoliation can result in a
reduction in the tree’s growth rate or even lead to the eventual death of the tree.
The European starling (Sturnus vulgaris) is an exotic bird species established in North America during the
mid to late 1800s as part of a plan to introduce all of the birds mentioned in the works of Shakespeare to
Central Park in New York City. It has since spread throughout the United States. In addition to competing
with native bird species for food and space, large flocks of this species destroy fields of crops. The house
sparrow (Passer domesticus) was introduced to several places in the United States in the late 1800’s and has
become widely distributed. In addition to causing crop damage, house sparrows will sometimes kill native
adult cavity nesters and their young or smash their eggs. The house sparrow is partially responsible for a
decline of eastern bluebirds (Sialia sialis) in the United States.
Feral swine (Sus scrofa; also called wild hogs) are potentially one of the most influential upcoming invasive
species for Pennsylvania forests. Escaped or deliberately released swine now exist in relatively low numbers in
Pennsylvania. Feral swine can impact livestock and cause significant ecological and property damage. This
includes rooting and destruction of native herbs and trees, and the creation of significant erosion from wallowing
Connecticut Agricultural Experiment
Station Archives
Hemlock Woolly Adelgid infestation along a hemlock
branch. This invasive species is currently causing a severe
decline (>90%) of native hemlock stands, an important
habitat type in Pennsylvania.
Pike County Natural Heritage Inventory – Natural History Overview / 17