Invasive Species

The study of introduced species which have become markedly successful, is now an important focus within ecology (Soule 1990). An introduced species is any species which is not native to a region. The advent of global transportation (boats, planes, cars, etc) caused increased transmission of species between regions, countries, and even continents. Although species may be benign in their native habitats, some succeed in their new habitats, and become invasive.

There are no “official” criteria for being considered an invasive species, but for plants, usually this designation indicates at least one of the following characteristics: effective reproduction, superior competitive ability, few to no herbivores or parasites, ability to occupy an unused functional group within a population, and the ability to alter a site’s resource availability (Gordon 1998). Well known examples of invasive species include the zebra mussel (Dreissena polymorpha) invasion of the great lakes and the purple loosestrife (Lythrum salicaria) invasion of American wetlands (Blossey and Notzold 1995; Gillis and Mackie 1994).

Alliaria petiolata, garlic mustard, is an exotic plant native to Europe. It is a biennial plant – the first year, it grows low to the ground; it overwinters, and then sprouts up a stalk, produces flowers and then a LOT of seeds in its second year. Garlic mustard is often identified by crushing new leaves – they smell, well, garlicky!

It is believed that garlic mustard was used by Europeans as an herb; however; now garlic mustard runs rampant through the understories of northeastern American forests. It crowds out native mustards and other spring wildflowers; and because it is long lived and evergreen, it can often take up space utilized by other plants, too.

In addition, garlic mustard has been noted as a “population sink” for the West Virginia White butterfly. In this case, garlic mustard is a population sink because its smell entices West Virginia White butterflies to lay eggs on it; but the caterpillars cannot survive.

One of the biggest threats to this butterfly is the invasion of garlic mustard into their habitats.

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Do you know the about these butterflies? Test your knowledge of Pieris virginiensis with this video.


There are two major native plants that support the West Virginia White butterfly's development.

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Visit Don Cipollini's lab website for opportunities to work with the West Virginia White butterfly as a graduate student.


As long as they've been a species, West Virginia Whites have been under threat of extinction.


Visit Sam's blog to discover what she's up to now, after leaving Wright State University in May, 2015 with her Ph.D.

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