The genus Lymantria includes moths whose larvae, or caterpillars, are notorious for their voracious appetites, particularly the species Lymantria dispar, also known as the spongy moth. The focus is almost entirely on this larval stage, as it is the only one that consumes plant material. These caterpillars are widely recognized as highly destructive defoliators, capable of stripping the leaves from entire forests during population outbreaks. The sheer volume of foliage consumed by the larval stage defines this insect as a major forest pest across its native and invasive ranges.
The Polyphagous Diet of Lymantria Caterpillars
The diet of Lymantria caterpillars is best described as polyphagous, meaning they feed on a remarkably wide variety of plants. The larvae of Lymantria dispar alone have been documented to consume the foliage of over 500 different species of trees and shrubs. This generalist feeding strategy allows them to thrive in diverse environments, from managed orchards to dense hardwood forests.
While they can survive on hundreds of plant types, their consumption is organized into a hierarchy of preference. This distinction separates “preferred hosts,” which support healthy growth and reproduction, from “acceptable hosts,” which are eaten when preferred sources are scarce. The vast majority of their diet consists of broadleaf deciduous trees.
This broad diet makes the caterpillars particularly damaging in non-native regions, such as North America. There, they exert immense pressure on local flora that did not co-evolve defenses against such a generalist feeder. A single outbreak can lead to massive, rapid defoliation, stressing or killing many trees.
Specific Host Plant Preferences and Avoided Species
The feeding preferences of Lymantria caterpillars are strongly skewed toward certain tree groups, even within their broad dietary range. The most important host plants are species of oak (Quercus), which are frequently cited as the favored food source for the larvae. Other highly consumed hardwood species include willow (Salix), birch (Betula), poplar (Populus), and apple (Malus), along with other fruit trees in the Rosaceae family.
These preferred hosts provide the best nutritional quality for the caterpillars, allowing them to complete their development with high survival rates. In addition to these primary hardwoods, they readily consume foliage from basswood, sweetgum, and alder. During severe outbreaks when the preferred trees are defoliated, the caterpillars will shift to less desirable species.
The consumption of conifers is a notable aspect of their diet, though these are only eaten by the older, larger larvae. Younger caterpillars often cannot survive on the foliage of conifers, but late-instar larvae will consume the needles of pines (Pinus), spruces (Picea), and hemlocks (Tsuga). Conifers are generally less resilient and may die after a single complete defoliation, unlike deciduous trees that can re-sprout leaves.
Certain tree species possess chemical defenses that make them highly resistant or even rejected by the caterpillars. The tulip tree (Liriodendron tulipifera) is consistently rejected by the larvae. Other species that are avoided or consumed only as a last resort include American beech (Fagus grandifolia), black walnut (Juglans nigra), and ash (Fraxinus). The reduced consumption of these species is often attributed to the presence of secondary compounds, such as alkaloids and flavonoids, in their leaves.
Feeding Behavior Across Life Stages
The diet and feeding methods of the Lymantria caterpillar change significantly as the insect matures through its larval instars. Newly hatched larvae are tiny and immediately climb to the tree canopy, often dispersing to new plants by spinning a silk thread and being carried by the wind, a process called “ballooning.” These young caterpillars, typically the first three instars, feed only on the most tender, newly emerged leaves and are the most selective about their host plants.
As the larvae grow into their later instars, particularly the fourth through sixth stages, their feeding becomes much more aggressive and less selective. These older caterpillars develop massive appetites and are capable of consuming tougher, older foliage as well as the needles of conifers. A significant behavioral shift occurs where the larger larvae often feed primarily at night in the canopy to avoid predators and the heat of the day.
During daylight hours, these larger caterpillars crawl down the tree trunk to rest in protected, shaded locations, such as bark crevices or under branches. This dramatic feeding over a period of about six to eight weeks is responsible for nearly all the defoliation damage associated with the species. Once the larval stage is complete, the insect pupates, and the emerging adult moths do not feed. Adult Lymantria moths lack functional mouthparts and exist only to mate and lay eggs.