When someone mentions webs, you probably immediately think of spiders, but there are many other critters that also spin webs. Think of spider mites or silk worms. But some, such as tent caterpillars (AKA tent worms), aren’t as well known despite having a reputation.
But what are tent worms, and should you worry if you see them in your trees?
Today, we’ll take a look at getting rid of these insects, as well as how to keep them away. Then we’ll take a deeper dive into common tent worm species and when they may or may not be a threat to your plants.
Getting Rid of Tent Caterpillars
Depending on the severity of your infestation, it’s surprisingly easy to remove these critters – provided you catch them at the right time of year. Let’s look at some common methods in the order of light infestations to heavy ones.
Related: How to Get Rid of Bagworms
Pluck Them
With smaller trees (or if you have a long ladder), mild infestations can be dealt with by hand. Throw on a pair of gloves to pluck off the egg casings in late autumn or winter.
You can also pluck cocoons or caterpillars as you find them and drop them in a bucket of soapy water. In early spring, you can take a stick and use it to wind up nests, capturing unhatched eggs and freshly hatched caterpillars alike.
Natural Predators
These pests have a number of natural enemies, especially birds and parasitic wasps. Blue jays, cardinals, chickadees, nuthatches, robins, and woodpeckers are all known to enjoy tent worms.
Conversely, you can employ microscopic assistance. Bt (Bacillus thuringiensis) is perhaps the most popular solution, although you will need to use some care in applying it. Furia gastropachae is a fungus that mostly affects the Malacosoma genus and is directly linked to a decline in the forest tent caterpillar.
- Size: 16 OZ
- Thuricide BT Caterpillar Control concentrate is used by organic gardeners and is...
- Safe to use on all plants, vegetables and edible crops.
Finally, you can attack the caterpillars or nests directly with a neem foliar spray or use a neem soil soak to take out these bugs when they try to munch on leaves. When used at dusk or dawn, neem posts minimal risk to beneficial insects and works on a wide range of bugs without being toxic to humans.
Natural enemies work best on small infestations, but can also help control larger populations to make them more manageable.
Chemical Insecticides
Generally a last resort, there are a number of insecticides out there that work on tent caterpillars. Suspend SC and Talak (aka: Talstar) one of the most recommended Aim for products that have azadirachtin, pyrethrin, or spinosad as the active ingredient, as these are all effective and at least partially organic.
Just be warned that insecticides tend to be indiscriminate, so you may be harming beneficial bugs as well as the target critter.
- Broad-spectrum control of more than 50 nuisance pests
- Effective knockdown with a long residual
- No odor, no visible residue
Preventing Tent Caterpillars
Pruning is perhaps the easiest way to discourage moths from laying their eggs. You may wish to consult a professional arborist to determine which branches are most at risk of being nested on. However, even a general pruning during mating season can help convince moths from picking that tree.
Regular watering during drier months might not stop an infestation, but it’ll make the trees more resilient. Additionally, you can use a hose or sprayer to dislodge egg cases or scare off moths. Natural predators are also an excellent way to keep infestations from forming.
Finally, regular use of neem products as a preventative can go a long way towards stopping infestations before they can gain a foothold.
Related: How to Get Rid of Caterpillars In the House
Getting to Know Tent Caterpillars
There are three major species of tent caterpillar in the US, each of which has its own preferences and appearance. Knowing what species you’re dealing with can go a long way in determining how big a risk they pose to your plants.
Identifying Tent Worms
Eastern Tent Caterpillar (Malacosoma americanum)
Despite the name, this species is found throughout much of the US and southern Canada, stopping at the Rocky Mountains. The caterpillars are black with a row of pale blue spots on their sides, a white stripe down their back, and sparse hairs.
They can measure up to two inches long. The adult moths have a 1 1/2 inch wingspan, are reddish brown, and the forewings have two white bands running diagonally.
This species prefers apple, crabapple, and cherry trees but will also infest a range of shade trees. They’re among the first to hatch and their tents are considered the largest, usually facing southeast to catch the morning sun. It should also be noted that this species is toxic to horses and is a cause of mare reproductive loss syndrome.
Forest Tent Caterpillar (Malacosoma disstria)
These hardwood-loving caterpillars are easily confused with the eastern tent caterpillar, except they have white keyhole-shaped markings instead of a solid line.
They can grow up to 2 1/2 inches long and sometimes appear dark brown or gray. They also have thin yellow lines alongside the blue markings. Adults have a 1 1/2 inch wingspan, but are tan to yellow with a thick dark band on their forewings.
They prefer aspen, cherry, hawthorn, oak, sugar maple, sweetgum, and tupelo trees. Unlike other tent worms, this species creates silken mats.
Western Tent Caterpillar (Malacosoma californicum)
Found along the western portions of North America from southern Canada to northern Mexico, this species has a highly variable appearance appearance. Measuring up to two inches long, they usually have a pale blue head and black bodies or black markings.
Pale blue markings or coloration is also possible, and they usually have a pale bluish white mid-dorsal stripe that has a band of black or yellowish orange to either side, with a band of black outside of that.
Adults are just as varied, ranging from a dark reddish brown to tan, yellow or gray. A pair of lines on the forewings may be either darker or lighter in hue. There are at least six confirmed subspecies with several potential subspecies yet unclassified.
As with their appearance, this species has a much wider range of preferred plants, including:
- Alder
- Bitterbrush
- Ceanothus spp.
- Chokecherry
- Cottonwood
- Crabapple
- Fruit trees
- Mountain mahogany
- Nine-bark
- Oak
- Poplar
- Quaking aspen
- Serviceberry
- Sumac
- Wild currant
- Wild rose
- Willow
Life Cycle
The exact life cycle will vary from one species to the next, but the eastern tent caterpillar is frequently used as the example, since it’s the best documented US species.
Eggs hatch in early spring, with the larvae going through five or six instars. Each new instar produces less silk, although the first instar usually requires a group effort to establish their nest. These pests are highly social and will send scouts to look for sources of young leaves, dropping a scent trail much like ants. It takes around eight weeks for the caterpillar to fully develop.
The pupal stage takes place in a sheltered area and lasts about two weeks. Usually the males are first to emerge and will seek out females who are emitting pheromones to show availability.
The female will lay up to 300 eggs the same evening she’s fertilized, protecting the mass with a frothy substance known as spumaline. She dies soon after, although the males may live up to a week after emerging.
Larvae form within about three weeks but overwinter in the egg until spring arrives. However, the exact size of successful eggs and speed of development often rely on weather and food availability, so tent worms will be worse some years than others.
How Dangerous are Tent Worms?
With the exception of the eastern tent caterpillar’s toxicity to horses, tent worms are more of a nuisance than an actual threat. The damage they do to healthy fruit or ornamental trees tends to be mostly cosmetic, and the foliage recovers once an infestation has been dealt with.
As tent caterpillar infestations survive on young leaves, there’s a limit to their destructive capabilities and mature leaves are left untouched.
Trees only become threatened if they’re young, in poor health, or there are large tent caterpillar populations that year. Defoliation can also weaken the trees, making them more susceptible to disease if enough leaves are damaged.
Other Concerns
The pupal stage often presents an additional risk. Tent worms are known to build their cocoons under the eaves or siding of homes. While this doesn’t do any harm on its own, a crushed caterpillar will leave behind a nasty stain that can ruin paint.
Also, while not common, dislodged tent worms have been known to build their nests on roads, resulting in a potential slip hazard.
Tent Caterpillars vs Gypsy Moth Caterpillars
While tent caterpillars can be a nuisance, they’re sometimes confused with gypsy moth caterpillars (Lymantria dispar). Despite some similarities, these are quite different creatures with distinct characteristics and behaviors.
Tent caterpillars are social insects that build distinctive silk nests in tree crotches or branch unions, while gypsy moth caterpillars are solitary feeders and don’t create silk tents at all. You can easily tell these pests apart by their appearance.
Gypsy moth caterpillars have distinctive pairs of colored spots along their backs – five pairs of blue spots followed by six pairs of red spots, along with long black hairs. In contrast, tent caterpillars have simpler markings (usually a white stripe or keyhole shapes) and much shorter, sparser hairs.
Another key difference is their destructive potential. While tent caterpillars primarily feed on young leaves and rarely cause permanent damage to healthy trees, gypsy moth caterpillars consume both young and mature foliage and can completely defoliate trees, sometimes fatally if infestations occur several years in a row.
Gypsy moth caterpillars can also cause skin irritation in some people due to their numerous hairs, while tent caterpillars rarely cause such reactions.
Tent Worms vs Fall Webworms
While these two critters are often confused, they are quite different. Fall webworms (Hyphantria cunea) appear from late summer into early fall. They range greatly in coloration and build their nests at the tips of branches rather than at the base.
The web tents are also much messier than with tent worms. Orange is much more common on this species than on tent worms, and they have longer, more numerous hairs.
The adults are mostly white and very fuzzy, with yellow or orange patches on the forelegs. In warmer climates, the forewings may also have darker spots.
Morgan is a certified entomologist and pest control consultant and a member of the National Pest Management Association.
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