Lymantria dispar is an invasive species that was first introduced to the United States in 1869. L. dispar has slowly spread across the United States and the first outbreak in Michigan was in the mid-1980's in central lower Michigan. At this time, L. dispar has become established in all Michigan counties.
L. dispar caterpillars, the immature "larval" stage, feed on leaves of more than 300 species of trees, but they especially like oak. Their population can be controlled by natural means, such as predatory insects and fungal disease. However, when natural methods cannot keep pace with the population growth an outbreak occurs. During outbreaks, the L. dispar population can grow in size, which can lead to defoliation of mature trees.
You are the first line of defense for protecting your property from damage by L. dispar. Take time to inspect your trees, shrubs, structures, lawn objects, and recreational vehicles periodically for the various life stages of L. dispar. Caterpillars can easily be identified by the 5 pairs of blue dots on their backs followed by 6 pairs of red dots (see image below). The caterpillars pupate in summer, emerge as adult moths, mate, lay eggs and then die. Egg masses, which are laid in summer on outdoor objects and tree trunks, persist for approximately nine months until the following spring. Egg masses are about an inch wide and up to two inches long, are buff or tan in color, and appear slightly fuzzy (see bottom image).