Spongy moths (formerly called gypsy moths) and tent caterpillars are different insects that cause different types of damage, and the easiest way to tell them apart is their “nests.” Tent caterpillars build prominent silk tents in the forks of tree branches. Spongy moths never spin webs or make silken nests at all. If you see a web structure in your tree, it’s not a spongy moth.
What spongy moths do leave behind are tan, fuzzy egg masses stuck to tree bark, which look nothing like the dark, shiny egg cases tent caterpillars wrap around twigs. Knowing which pest you’re dealing with determines what trees are at risk, when the damage will happen, and how to manage it.
How the “Nests” Look Different
Eastern tent caterpillars build thick, conspicuous silk tents in the crotches and forks of branches. These webs are tightly woven and grow larger as the caterpillars grow, sometimes reaching the size of a football by late spring. The caterpillars don’t actually feed inside the tent. They use it as a resting spot at night and during rain, then leave to eat leaves during the day.
Spongy moth caterpillars produce no silk tents whatsoever. If you’re seeing caterpillars on your trees but no webbing, spongy moth is a strong possibility. Instead of building a communal shelter, spongy moth caterpillars hide individually in bark crevices, under branches, or beneath debris during the day, then climb up to feed at night (though during heavy infestations, they feed around the clock).
There’s a third species that causes confusion: the fall webworm. Its webs are loose, dirty-looking, and enclose the tips of branches rather than sitting in branch forks. Fall webworms also show up in summer and fall, while tent caterpillars appear in spring. Forest tent caterpillars, a close relative of the eastern tent caterpillar, don’t build silk tents either. They sometimes leave a thin silk mat on leaves or bark where they gather, but nothing resembling the obvious tent structure.
Egg Masses: The Winter Clue
Both species overwinter as eggs, so fall and winter are ideal times to identify which pest you’ll be dealing with come spring.
- Spongy moth egg masses are tan or buff-colored, 1 to 3 inches long, and covered in fine, felt-like hairs that give them a spongy texture (hence the new name). They’re laid on tree bark, but also on outdoor furniture, firewood, vehicles, and building walls. They look like small patches of tan velvet stuck to a surface.
- Tent caterpillar egg masses are dark, spindle-shaped bands wrapped tightly around small twigs. They have a hard, varnished appearance, almost like dried shellac. You’ll find them on the smaller branches of host trees, not on flat surfaces like tree trunks or buildings.
This is the most reliable identification method. If you find fuzzy tan patches on your tree trunks or on objects near your trees, those are spongy moth eggs. If you find dark, glossy bands circling thin twigs, those belong to tent caterpillars.
The Caterpillars Themselves
Once the larvae emerge in spring, the caterpillars look quite different from each other. Eastern tent caterpillars grow to about 2 inches long, are black with white and blue markings, and have a distinctive white stripe running down the center of their backs. They’re sparsely hairy and tend to move together in groups.
Spongy moth caterpillars are hairier and more colorful. They have five pairs of blue spots near the head followed by six pairs of red spots running down the back. Young larvae are dark and very small; older larvae are more boldly marked and can grow quite large. Unlike tent caterpillars, they don’t travel in organized groups, though during outbreaks they can cover tree trunks in alarming numbers.
When Each One Appears
Both species hatch in early spring around bud break, so there’s significant overlap in timing. Eastern tent caterpillar eggs typically hatch in April, and the caterpillars begin spinning their tents almost immediately. By late spring the caterpillars are fully grown, and adult moths emerge about two weeks after pupation. There’s one generation per year.
Spongy moth caterpillars hatch when oak buds are opening, which is roughly the same window depending on your location. Young larvae chew small holes in leaves, while older larvae eat from the leaf edge inward, eventually stripping entire branches. Spongy moths also produce one generation per year.
The key seasonal difference involves fall webworms, which people often lump into this group. Fall webworm eggs don’t hatch until mid-July, and the caterpillars feed through summer and into fall. If you’re seeing webs in August, that’s a webworm, not a tent caterpillar.
Which Trees Are at Risk
The two pests target different trees, which is another useful identification clue.
Eastern tent caterpillars strongly prefer cherry, apple, and crabapple trees. They’ll also feed on other fruit trees, as well as ash, birch, maple, oak, poplar, and occasionally beech or willow. If your silk tent is in a wild cherry tree, eastern tent caterpillar is the most likely culprit.
Spongy moths prefer oaks above all else, but also attack apple, sweetgum, alder, basswood, birch, poplar, and willow. Older larvae will even feed on conifers like hemlock, pine, and spruce. During heavy outbreaks, they become far less picky and will feed on nearly any tree or shrub. They tend to avoid ash, sycamore, black walnut, and evergreen shrubs like rhododendron and mountain laurel.
Damage Patterns
Tent caterpillar damage is usually cosmetic. The caterpillars feed in colonies on one branch at a time, and healthy trees typically leaf out again by midsummer. The silk tents are unsightly, but the overall defoliation is usually limited to a portion of the tree’s canopy.
Spongy moth damage can be far more severe. During population outbreaks, caterpillars can completely strip a tree of its leaves. You’ll notice heavy frass (caterpillar droppings) raining down from the canopy, which is a telltale sign. One year of complete defoliation usually won’t kill a healthy deciduous tree, but two or three consecutive years of heavy feeding can, especially for oaks and conifers that don’t recover as easily.
How to Remove Them
For both species, the most effective approach is removing egg masses during fall or winter, well before the caterpillars hatch in spring.
Scrape egg masses off branches or bark into a bucket of soapy water and let them soak. For tent caterpillar eggs wrapped around twigs, you may need to scrape firmly since they’re bonded to the wood. For spongy moth egg masses on bark or flat surfaces, a putty knife or stiff brush works well.
If you missed the egg masses and tent caterpillars have already built their webs, pull the entire tent off the tree by hand (wear gloves) and drop it into soapy water. This is easiest in the early morning or evening when the caterpillars are gathered inside. For tents that are too high to reach, tearing them open exposes the caterpillars to birds and other predators, which provides some natural control.
Individual caterpillars of either species can be handpicked and dropped into soapy water. For spongy moths, wrapping tree trunks with burlap bands in late spring creates a daytime hiding spot that you can check and clear daily, since the caterpillars crawl down the trunk each morning to shelter.
About the Name Change
In March 2022, the Entomological Society of America officially replaced the common name “gypsy moth” with “spongy moth.” The word “gypsy” is considered an ethnic slur for the Romani people, and the name change was the first undertaken by ESA’s Better Common Names Project. The new name comes from the French common name “spongieuse,” which refers to the sponge-like texture of the insect’s egg masses. You’ll still see both names widely used, but “spongy moth” is now the standard term in scientific and extension publications.