Two diseases that affect spongy moth, formerly gypsy moth, caterpillars are the most important factors causing outbreaks to collapse. One disease is a nucleopolyhedrosis virus (NPV) and the other is a fungus called Entomophaga maimaiga.
Surveying spongy moth, formerly gypsy moth, egg masses, which are present for nine to 10 months every year, provides a means for pest managers to estimate how high a spongy moth population is likely to be the following year.