The northern leopard frogs that inhabit the boreal U.S. have
never recovered from some catastrophic population declines in
the 1970s. Some blame it on the acidifying lakes and streams
caused by coal-burning, others point to the ongoing loss of
wetlands to development, and now new evidence shows that the
herbicide atrazine—widely sprayed on crop fields throughout the
region—is killing the frogs by helping parasitic worms that
feast on them. "Atrazine provides a double whammy to frogs: It
increases both amphibian exposure and susceptibility," says
biologist Jason Rohr of the University of South Florida in
Tampa, who tested the impact by re-creating field conditions in
300-gallon (1,135-liter) tanks in his lab. "Atrazine is one of
the more mobile and persistent pesticides being widely applied.
In fact, residues have been found in remote, nonagricultural
areas, such as the poles." That may explain why amphibians are
on the decline worldwide. As many as one third of the nearly
6,000 known amphibian species—frogs,