The Invaders by Mark Sanchez
During the early 1900s, two kinds of invasive organisms turned up in waterways in the United
States. One was the Asiatic clam, a fast-growing shellfish that crowds out other aquatic animals.
The other was milfoil, a fast-growing aquatic plant that overcomes and displaces native water
plants.
Wildlife officials are seeing once-smooth freshwater beaches littered with sharp, tiny shells. Though
Asiatic clams are rarely larger than 1.5 inches across, the sheer number of the shells is cause for
concern. The highest populations occur near power and wastewater plants. The clams cause problems
by biofouling, or clogging intake valves. Biofouling also occurs in irrigation canals and pipes and
drinking water facilities. Repairing damage caused by Asiatic clams is expensive. Experts estimate
that the price tag has reached one billion dollars per year in the United States.
(continued)
Explore how to answer this question: "How can I best summarize this bulletin?"
The author presents a central idea in each paragraph but does not state it directly. The important text
details support the central idea, so identifying them will help you determine the central idea. This in
turn will help you summarize the text.
Reread the bulletin. Underline the important details. Then fill in the missing information below.
Central idea of paragraph 2: Biofouling by Asiatic clams, one type of invasive species in U. S. waterways,
causes costly repairs to industrial and agricultural water facilities.
Important detail from the text: