The spongy (gypsy) moth is an especially devastating insect because of what it feeds on and because it reaches such high numbers is such a short period of time.  Oak, aspen, birch, apple, white pine and spruce are some of our favorite trees and are also fed upon by the spongy (gypsy) moth.  This might be tolerable if the moth would remain in low numbers like many other forest dwelling insects.  But the spongy (gypsy) moth has a very high reproductive rate and the caterpillars are not eaten by many predators, so a large percentage of the caterpillars continue to feed all season long.  A single pair of spongy (gypsy) moths can develop into millions of individuals in just a few seasons.  With that many caterpillars around, there are bound to be some problems.
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Two levels of spongy (gypsy) moth infestation are generally recognized.  The first level is "nuisance" and occurs when home owners notice shredded leaves continually raining down from their trees, frass (excrement) on horizontal surfaces, obnoxious abnormal smells, and see caterpillars everywhere as the leaves on their trees become thinner and thinner.



The second level of spongy (gypsy) moth infestation is "tree damage".  This level is beyond nuisance, when the number of caterpillars actually affect tree health.  When trees are fifty percent or more defoliated early in the season, they suffer.  Tree growth is stopped or much reduced, they must draw on starch reserves to put out new leaves late in the season, and they become more susceptible to drought, other insects, and diseases.  Normal, otherwise healthy trees, can withstand one season of defoliation but successive years without sufficient time to recover is very stressful and some trees may be lost.