of pine species and 90 percent of mature hemlocks because conifers do not store energy in their roots; an exception is larch. Factors that affect gypsy moth populations Natural predators play an important role during periods of low population. Predators include wasps, flies, ground beetles, ants, many species of spider, several species of birds such as chickadees, blue jays, nuthatches, towhees, and robins and approximately 15 species of common woodland mammals, such as the white-footed mouse, shrews, chipmunks, squirrels, and raccoons. Small mammals are the largest predators in low density gypsy moth populations and are apparently critical in preventing outbreaks. Calosoma (ground beetles of European origin), cuckoos, and flocking birds such as starling, grackles, and red-winged blackbirds, are attracted to infested areas in high gypsy moth population years. Biological control Diseases caused by bacteria, fungi, or viruses contribute to the decline of gypsy moth populations, especially during periods when populations are dense and are stressed by a lack of preferred foliage. Wilt disease caused by a particular nucleopolyhedrovirus (LdNPV) that is specific to the gypsy moth is its most devastating natural disease, causing a dramatic collapse of outbreak populations by killing both the larvae and pupae. Larvae infected with wilt disease are shiny and hang limply in an inverted "V" position. Infection with NPV is the most common source of mortality in high density populations and NPV epizootics usually cause the collapse of populations. Since the 1980s, the fungus Entomophaga maimaiga has also had a large impact on gypsy moth populations in North America. Weather conditions can affect the survival and development of gypsy moth life stages, regardless of population density. Temperatures of −20 °F (−29 °C.) lasting from 48 to 72 hours can kill exposed eggs; alternate periods of freezing and thaw in late winter and early spring may prevent eggs from hatching; and cold, rainy weather inhibits dispersal and feeding and slows the growth of newly hatched larvae. Gypsy moth larvae have several predators which can help decrease their population. Lack of predation is one reason they can change from being a normal part of the ecosystem to an actual threat to trees. Among their predators are: Deer mice – are considered the most important predator of low-density gypsy moth populations and their abundance may be critical in determining whether populations go into an outbreak mode. Their abundance is strongly affected by the amount of mast (e.g., acorns)