There are many plants and animals in any area that are
non-native. These typically range from desirable introduced species such as
pheasant to those labeled invasive and noxious. It is easy to see how the
desirable species get transplanted. In my area there is a large local goose
population that was started by one person who thought it would be nice to have
a local population. Where we once had a
migratory population, we now have geese that nest here and spend their entire
Strangely enough, species that are later labeled invasive,
noxious and so on, are sometimes introduced with similar good intentions.
English sparrows and starlings were brought to this country by someone who
thought it would be nice to have all of the birds mentioned in Shakespeare’s
works living in America.
Other species that become pests are accidently introduced.
Many of the weeds that are now classified as noxious apparently were introduced
in imported hay, bedding and feed as seeds. A current concern is the spread of
various aquatic plants and invertebrates such as snails that are moved from
waterway to waterway on boats, trailers and other equipment. Obviously weed
seeds, snail eggs and tiny organisms are difficult to control and easily spread
in other activities.
According to the USDA, an invasive species is a non-native
or alien species whose introduction causes or is likely to cause economic or
environmental harm or harm to human health.
They note that the vigor of invasive plant species combined with a lack
of natural enemies can lead to outbreak populations.
You have probably heard in the news about some of the
species listed as invasive on the USDA web site: Africanized honeybees,
Mediterranean fruit fly, soybean cyst nematode, Burmese python. Once a species
is considered invasive, it is usually opposed with regulations. Before a species reaches the level requiring
regulation, we can all do our part. Do not release or allow the escape of
animals, particularly exotic pets. When dealing with natural materials that could
contain unwanted seeds, eggs or tiny organisms, be sure that you are working
through legitimate business channels. Even buying plants at nurseries, for
example, may not ensure that you don’t receive some unwanted seeds or organisms
in the soil. More casual sources, such as buying an exotic potted plant at a
flea market, will certainly not ensure unwanted pests.
Nursery catalogues sometimes contain notes that particular
plants cannot be shipped to specific states. These guidelines are sometimes in
places to prevent the sale of nursery stock into areas where it can become
I purchased water hyacinth for a decorative pond. By the end
of summer, I was raking it off the pond and allowing it to dry out and die off.
After a winter of freezing weather, I no longer had water hyacinth. In a warm
climate, I can imagine it taking over every square inch of water surface and
living from year to year. Water hyacinth
may overgrow in our zone 10 but in other areas they can likely can overwinter
and become invasive.