Photo © Randy Westbrooks U.S. Geological Survey www.invasive.org Aquatic Pest—Zebra Mussels Zebra mussels were discovered in 1988 in the water connecting Lake Huron and Lake Erie. Within two years they were found in all the Great Lakes. By 2002, 20 eastern states reported the occurrence of zebra mussels. While no live colonies are currently reported in the Pacific Northwest, zebra mussels were recently found on a recreational boat and a trailer in eastern Washington. They breed prolifically, and can live for several days out of water in cool or humid conditions. If this mussel were introduced in Idaho, it could have disastrous effects on irrigation systems (by clogging sprinklers and reducing flows in pipes), on hydroelectric power plants, and on fish ladder structures for salmon in the Clearwater, Snake, and Columbia River drainages.

The Threat of Invasive Species

Idaho has benefited greatly from the introduction of many nonnative species of plants and animals and suffered from others. It would, indeed, be hard to envision an economy or a lifestyle in Idaho without potatoes, chukar partridges, apples or wheat—all species that evolved elsewhere and were brought to this state. On the other hand, there are species of plants, animals and microorganisms that have caused great damage to the state. For example, white pine blister rust has completely changed the composition of north Idaho’s forests while cheatgrass encroaches on thousands of acres of otherwise productive rangelands. These, too, are nonnative species that arrived in Idaho by accident, but once here, thrived by destroying or displacing far more desirable native species.

Introduced species that escape their intended niche or which are unintentionally brought to the state and then cause either economic or ecological harm are termed “invasive.” Idaho is vulnerable to such species, due to the variety of climates and habitats as well as the vast rural areas where invasions can spread unnoticed until eradication is too late. The danger is magnified by recent growth in numbers of visitors to Idaho as well as in interstate and international commerce. As Idaho’s connections to the rest of the world increase, so does the pace of new infestations by undesirable, nonnative species—ranging from noxious weeds to insect pests.

There are two types of invasive species—those not here but are likely to arrive, and those here now that have proven to cause damage and which may multiply or spread to areas of the state where they are not now found. Both types arrive through a variety of invasion pathways. People buy “exotic” pets or fish and allow them to escape to the wild. Boats or boat trailers harbor aquatic animals or weeds and then transfer them to Idaho’s waters. Imports of agricultural products or nursery stock can bring insect pests or diseases, and visitors from other countries may inadvertently bring seeds, insects or disease organisms with them. Once here, these new organisms can spread in numerous ways. Livestock and recreational vehicles carry weed seeds to new areas, as can the wind. Aquatic plants and animals can simply float downstream, and many species spread the “old fashioned way”—reproducing and moving into areas they do not currently occupy.

The enormous impact of these invasions is already evident as invasive species have damaged Idaho’s rangelands, waterways, farms, forests, and urban environments. They even threaten human health. Noxious weeds like yellow starthistle infest vast areas of formerly productive rangelands in Idaho— displacing wildlife and reducing livestock grazing. Eurasian watermilfoil chokes swimming and boating areas in several popular lakes. Hawkweed is out-competing tree seedlings in northern Idaho forests. Cereal leaf beetle has cost Idaho wheat farmers thousands in crop damage and control costs. Dutch elm disease has decimated elm trees that once graced city parks. And the West Nile virus, which has not yet reached Idaho, can be deadly to humans and animals.

Other invasive species that have yet to reach Idaho could cause new and even more damaging impacts. Zebra mussels, a scourge in the Midwest, clog irrigation and power turbine intakes; the citrus longhorned beetle, originating in China and spreading to the United States in wood packing material or bonsai plants, is an urban pest. Once established, the beetles kill common shade trees and eradication requires the removal of all surrounding trees, devastating whole city blocks.