Releasing the weevils, an insect originally from Greece, is part of the district's resource management program to control and reduce the spread of the non-native invasive star thistle. The U.S. Department of Agriculture has stated that the hairy weevil effectively eats the star thistle and diminishes the plants ability to spread, thereby returning the preserve to its natural state.
Weevils were first introduced into the preserve in 1997, and monitoring of additional releases between 2004 and 2007 showed that the insects damaged 40 percent to 90 percent of the yellow star thistle seed heads, according to the district. Monitoring also showed that star thistle populations are sparser and smaller in the locations where they remain.
Weevils are a good method of controlling invasive weed growth where other methods such as mowing, burning and herbicide application are not feasible, according to the district.