In the caterpillar stage, gypsy moths cause all the damage. After hatching, the caterpillars may feed for up to two months on the leaves of trees. As they mature, they expand their diet (and their big appetite) and will ultimately continue to feed on trees and shrubs. The leaves of most oak species are their preferred food source, and populations won’t build up in areas that don’t have a reasonable oak tree population.
Heavy defoliation causes stress to the infested trees, making them susceptible to secondary attacks by other insects and pathogens, which can lead to plant death.
In this instance, it was a White Oak, that was killed by the insects.