Population cycle

Unlike most other forest insects, gypsy moth populations go through dramatic changes in abundance. Most of the time, their population is relatively low and you rarely see a caterpillar unless you look for one. Surprisingly, you can have up to 25,000 larvae per acre and not notice any effect on the trees! Every 7-15 years, however, the population will be "released" by a combination of favorable conditions and will increase at a very rapid rate. Typically, the population will continue to grow until there are so many larvae that they consume all the available food and start to starve. It's at this "outbreak" stage in their population cycle that we have problems with the gypsy moth. It usually takes only one to three years before starvation, disease, and natural enemies cause the population to crash back to low levels, but in the meantime a lot of damage is done to the trees.