What Are Gypsy Moth Caterpillars & How Do You Get Rid of This Pest?

This year, gypsy moth caterpillars have been a big problem where I live.

Much of the local economy around here is focused on maple syrup production, and since gypsy moth caterpillars are particularly interested in feeding on maple trees, this has been a major blow to maple growers.

Until this year, gypsy moth caterpillars weren’t something I’d ever heard of. However, it is very widespread, affecting trees in nearly every US state as well as much of Canada.

Here’s what you need to know about this destructive pest—and how you can keep your trees and plants safe.

What are Gypsy Moth Caterpillars?

Gypsy moth caterpillars are annoying pests in rural and urban areas as well as in wooded places. It is not the insect version of this insect that is so frustrating to deal with but instead the caterpillars, which are in the immature “larval” stage.

These caterpillars feed mainly on tree leaves, with oaks being the preferred species (although they will also eat many other types of trees and plants).

In some cases, the infestation is so severe that the trees are completely destroyed, with most feeding occurs in spring and early summer. They form reddish-brown cocoons at the end of the summer months and, by August, have developed into caterpillar moths. When moths emerge from the cocoon in July or August, they only live for a few days (enough to breed) but do not feed on trees.

Egg masses are laid in July or August, to overwinter, and then emerge the following spring to repeat the cycle again.

Which plants do they affect?

These creatures feed on over 300 species of trees, especially oak, maple, aspen, apple, birch, basswood, willow, and more.

Preferred species include:

  • acorn
  • willow
  • aspen
  • Apple
  • White birch
  • Tamarind
  • witch hazel
  • basswood
  • Mountain ash
  • a type of tree
  • Cedar
  • spruce
  • Maple
  • Walnut
  • hickory
  • chestnut
  • hemlock
  • cherry
  • elm
  • black and yellow birch
  • Middle
  • Cottonwood
  • ironwood
  • boxelder

Generally, caterpillars will avoid the following:

  • dogwood
  • sycamore
  • catalpa
  • tulip poplar
  • Red cedar
  • Scotch Pine
  • grasshopper
  • balsam fir
  • green, black or white ash

Symptoms of Gypsy Moth Caterpillar Infection

You will know that gypsy moth caterpillars are attacking your trees if you have the following symptoms.

The first is actually seeing the large, hairy caterpillars on the tree. They are very easy to spot – they have long, dark hair along with blue and red spots on their backs.

They can feed at any time throughout the spring or summer months, but the most active period for these pests is from late May to late July.

Gypsy moth caterpillars feed on tree leaves, biting a tree until it is partially or completely destroyed. This is one of the most obvious signs of gypsy moth caterpillar infestation – if a tree once had leaves and now doesn’t, it may be these pests to blame!

1. Other Tree Pests Similar to Gypsy Moth Caterpillars

This is the easiest way to differentiate these caterpillar pests from another common type of tree pest – the eastern tent caterpillar. This latter species also feeds in spring and summer, but differs in that it rarely causes a noticeable amount of discoloration. In addition, you will see the silky tentacles that these caterpillars make in the trees.

The same goes for the fall webworm, another insect that feeds on trees (but in late summer and fall) and forms silk webs. Again, although these pests may make your trees appear a bit on the unattractive side, they rarely cause complete discoloration.

2. The excretion is widespread

A tree that has been feasted by a gypsy moth caterpillar may look like it is dead. However, this is usually not the case. It will produce a second set of leaf buds and “leaf back out” by mid-summer. This second set of leaves should give your tree enough energy to get through the summer and the coming winter—that’s good news.

The bad news is that this kind of widespread severe fall can really put pressure on a tree. As long as your tree is mostly healthy, it should be able to withstand this storm—but if there are other stress factors involved, such as drought, disease, or unfavorable growing conditions, your tree may die.

Some tree species, especially conifers, cannot handle such extensive discoloration. They often die from heavy gypsy moth caterpillar infestations. Fortunately, the gypsy moth Aptera rarely feeds on conifers unless the population is very high and other preferred tree species have already been consumed.

stopping gypsy moth caterpillars

There are a few ways you can prevent gypsy moth caterpillars from destroying your trees. Here are some great options.

1. Find and Remove Egg Mass

It won’t do you any good to remove the egg mass this year, but the work you are doing now may help prevent an infestation of gypsy moth caterpillars next spring.

This summer and fall, check your property for egg mass. They can also occur on trees themselves or on surfaces such as firewood or outdoor furniture.

When you find them, scrape the egg mass into a bucket filled with soapy water. You can even bury or burn them. Whatever you do, just don’t leave them lying around – the winter weather won’t kill them and they’ll spawn next spring.

2. Pheromone trap?

Some people swear by using pheromone traps to eliminate gypsy moth caterpillars, but sadly, these are really only to detect the presence of these pests and not kill them. You can use pheromone traps to predict where the caterpillars might hang out, but don’t expect them to go away without other interventions.

3. Keep Things Clear

Keep your yard as clean as possible. This won’t necessarily help cut down on gypsy moth caterpillar numbers, but it can help you find the egg mass more easily.

4. Introduce Natural Enemies

Consider introducing some natural enemies (or encouraging them to visit) to deter gypsy moth caterpillars. Some of the most common include birds, rats, and various predatory insects. These feed on gypsy moths at various stages of life – there are even insect parasites that attack the gypsy moth’s eggs, pupae and caterpillars.

Avoid using broad-spectrum insecticides so you don’t accidentally kill these parasites or insects. In addition, make your landscape a suitable environment for birds and other natural predators by adding water features, driving out birds, and taking other steps to make your garden wildlife-friendly.

5. Use a Constraint

You can purchase a commercial barrier to place around tree trunks to reduce the movement of caterpillars in tree canopy. However, a simple solution that many people rely on is to wrap tree trunks (towards the base) with layers of double-sided duct tape.

The theory here is that the caterpillars will get stuck in the tape and won’t be able to work their way up to the canopy. It can be effective, but it may need to be reapplied frequently.

how to get rid of gypsy moth caterpillars

Gypsy moth caterpillars are very difficult to get rid of but there are some steps you can take.

One of the most popular routes is to spray Bt. bt, or bacillus thuringiensis bridegroom. kurstaki, is a spray that can be applied to the leaves of trees a week or two after hatching. Bt is most effective against young caterpillars and must be consumed by the caterpillars for it to be effective.

It is not harmful to humans or other animals, so it is a good idea to spray trees with it if you have a choice. Most insecticides will not do much against gypsy moth caterpillars and they may kill beneficial insects and pollinators in the process.

Ultimately, the only thing that is known to kill these caterpillars every year is a viral disease called nucleopolyhedrovirus disease, or NPV. The virus affects caterpillars and outbreaks usually subside after 2–3 years of heavy foliage. is a similar type of fungus, entomophaga mymaiga, which can kill a large number of caterpillars.

The good news is that you don’t have to do anything for these natural controls to take effect – you just need to be patient! While spraying Bt and trying the other preventative measures above can help reduce the effects of gypsy moth caterpillar infestations, the best thing to do while you wait for Mother Nature to arrive is to take care of your trees. And keep other plants healthy.

After all, a gypsy moth caterpillar infestation rarely kills a tree—unless the tree is already weak, to begin with. So make sure your trees have the nutrients, water, and other care they need, and you should be able to help them weather the storm!

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