The Leaf-Eating, Tree-Damaging, Little Green Caterpillar

Milan Zubrik, Forest Research Institute - Slovakia, Bugwood.org

Winter Moth, Milan Zubrik, Forest Research Institute – Slovakia, Bugwood.org

Remember the little pale green caterpillar that ate through your trees and roses last year? Well, it’s back!

The caterpillar stage of the invasive winter moth (Operophtera brumato) eats young, tender leaves, sometimes before the leaves even get a chance to emerge from the bud.

The winter moth caterpillar is just one of hundreds of species of tiny green caterpillars, or inchworms, found in North America. Most are native and ecologically helpful, even though some, like the winter moth, can be a nuisance.

Identifying Winter Moth Caterpillars

It’s easy to tell winter moths apart from beneficial inchworms. The best way is by looking at the back end of an inchworm: If it has only two pairs of legs on its back end, it’s probably a winter moth. More than two pairs of legs on its back end means it’s probably a “good inchworm” and should be let be.  Winter moths are also stouter than other inchworms, and have a white stripe along the side.

The Moth Stage

Last November and December you might have seen hundreds of moths on cool winter evenings flying around outdoor lights. They were the male moths. They were out looking for vertical surfaces, like tree trunks, to find the virtually wingless females and mate. Once the moths had mated, the females lay their eggs in the craggy bark of the trees.

The Caterpillar Stage

Through the winter months, the tiny eggs lay waiting for the perfect time to emerge. Early spring, when the temperature and day length are just right, the buds of trees start to open. This is also when the tiny pale green inch-worm-like caterpillars of the winter moth emerge. They then eat their way through the leaves while they are still in the emerging bud. The leaves emerge skeletonized with only their veins remaining or if the leaves had a chance to develop the leaves are peppered with holes.

Assessing the Damage

Most trees can handle a year of this leaf eating if there are not other forms of stress such as drought, insect infestation, or too much sun or shade depending on the tree. Often, they can send out a second flush of leaves. Remember trees and all plants need to have leaves; it is where the process of photosynthesis occurs (ie where the plants make their food).

Providing extra water throughout the season will help trees recover from the stress of defoliation and re-foliation,

What You Can Do

Most people ask what they can do about these leaf-eating caterpillars. Sure there are sprays that can eradicate them. But, keep in mind they are not selective. The spray that kills the caterpillar stage of the winter moth also kills all of the butterflies in their caterpillar stage.

Paper or plastic strips covered with a sticky substance are commercially available to create a barrier that entraps the adult females and caterpillars. Though logical, this method has not proven to be effective for major infestations.

One option is to not plant trees that are extremely affected by the winter moth. Instead of vulnerable trees like crabapples, pears, and weeping cherries, try planting native trees. After they are established, (generally a year), they will be more resistant to forms of stress and better able to withstand the damage done by the winter moth caterpillar.

Learn more about what you can do to control winter moths on our website.

Updated July 2018

58 thoughts on “The Leaf-Eating, Tree-Damaging, Little Green Caterpillar

  1. Iris Marie Bloom

    Please do not use Bt!!! It harms all caterpillars including monarchs; it gets in the soil and persists. Those of us working to protect pollinators have to work hard to find soil that is free of Bt. Please find another method. We need caterpillar diversity — it is vital for our ecosystem, for butterflies and also for birds. Thank you!!

    Reply
  2. Shecky Liebowitz

    Hang a hummingbird feeder so it occasionally drips onto a plant where you’ve seen a catapiller. Wasps will be attracted to the sugar. Once at the ice cream parlor he says hey, what’s that green thing over there? It ain’t pretty but Mr wasp will solve your prob

    Reply
  3. chance

    I have 5 caterpillars and have been feeding them and looking after them and one i got this morning it was tiny and now it is bigger

    Reply
  4. Ken

    Wash the leaves and bark with a hard stream of water. Start at the top and work your way down. Do this at night when they come out to eat. A few nights in a row works well. Watch the birds feast in the grass the next day.

    Reply
    1. Jessica

      I just found one that won’t let go of my gloves because it is cold and my gloves are so warm! It is so tiny and adorable! I’m going to take care of it and give it a home in my backyard on my tree.??

      Reply
  5. Sarah

    I have wasps around my yard / house and they seem to like eating them quite a bit. Maybe start a beehive of your own? I’m not sure if regular bees eat them but it’s worth finding out. Either way it’s a win win situation for you and the earth.

    Reply
  6. Dave

    The presence of Crows feeding daily on a paved driveway led to the discovery of what’s thought to be this caterpillar (there are definitely moths around the area) which seemed to have fallen from the canopy of an Elm tree over the past ~month. Juncos were later seen feasting on these caterpillars as well. They seem like an important food source for the birds.

    Reply
  7. Carry Wang

    Hi guys
    If you want to get rid of those caterpillars who eat your beautiful plants then don’t apart therm with anything just go to my website to see how to get rid of them. Thank you?

    Reply
    1. Frank barresi

      I have to midgetapple trees,a Fuji and a gala. What can I do to saftly stop black worms and green inch wowm from eating all the leaves. In the 4 years I have
      Had them, I got one apple and that had a worm in it.these are supposed to be midgets,but they are over 8ft,can I cut them lower.

      Reply
    2. Julia

      Carry Wang, why can’t u just say on the comments Or post ur website? I’m having alot of trouble even getting a few good leaves off my basil plants from the suckers and my plants are about a foot or so high with almost all leaves holes or veins only left n idk what to do. they looked beautiful n big n healthy a few weeks ago n wish I clipped them then but now there’s barely anything left to salvage and I only find caterpillars and moths on them as well as some leaf footed bugs

      Reply
  8. Steve

    Does anyone know if wrapping the trees with a band of cellophane would prevent the caterpillars from climbing up the tree and thus eating the leaves? Thx.

    Reply
    1. Lisa

      I wrapped my tree trunks in aluminum foil secured with duct tape and covered it with vasaline. They can’t climb through it.

      Reply
  9. Evelyn Bryant

    Bt is a bacteria that disrupts a caterpillar”s digestive system. and is generally effective for caterpillars. Treatment of choice for cabbage loopers and works great. They stop feeding and die within a few days. Also, don’t need to spray caterpillars directly. They ingest it from the leaves.

    Reply
  10. Brian Neagle

    We live in South Eastern Massachusetts and three of the last four years we have had these little devils defoliate our large Crab Apple tree, our Blue Berry bushes and two apple trees as well as destroy a Japanese Maple sapling about six years old. The first two years damage was done and we had little to no fruit, but the trees managed to send out new leaves and appeared to recover nicely. Then we had a year off where there was very little damage done and the fruit returned in abundance. This year it looks like a nuclear winter. The trees have produced maybe 25% new leaves since the onslaught. I am not sure any of my fruit trees or bushes will survive. I am hoping for the best.
    We love canning our small crop but this will be three out of four years without any fruit.
    I am wondering, after they have eaten their fill and silk threaded their way to the ground, do they stay in the soil, if so can they be controlled at that point or are they already back in the trees?

    Reply
    1. Hillary

      From Kathi: The winter moth caterpillar is doing all of the damage. As the winter moth goes through its life cycle, male moths fly around the lights in November and December and mate with wingless females on the bark of trees. The eggs overwinter in the crevices on the bark; when the temperature is right the eggs hatch out and crawl to the just opening leaf buds. If one were to spray, this would be the time-at bud break in the caterpillar stage. Please understand that what you spray would also impact bees, other pollinators, and butterflies in their caterpillar stage. After winter moths eat their fill of the leaves and have stored up enough energy, they go into their pupa stage, like a chrysalis in the butterfly life cycle, and they are difficult to detect.

      The reason why there was very little fruit was the plant needs the leaves to produce food (the process of photosynthesis) but it does not need to reproduce (flower and make seeds) every year. If the plant expended energy on making flower it would have no energy to push out another set of leaves. One way to help the plant/tree/shrubs is to make sure it is receiving a consistent amount of water to help with new leaf growth.

      Reply
  11. Mona Lisa

    If the tree or plant is small enough, you can shake them off every night. You have to shake really hard and you will see a literal rain of caterpillars falling on the ground. I had to wear a hat so they wouldn’t get in my hair! I do this to my weeping cherry that my kids and husband gave me one mother’s day. Spraying the plant HARD with the hardest setting of your hose get’s the rest of them. Obviously it is VERY to keep the plant strong with regular consistent watering in dry times and feeding, until the caterpillar stage passes. The tree or plant will send off new leaves. For me, the key was trying to salvage as many leaves as possible so that the plant could still have photosynthesis happening in the remaining leaves. I inspect the affected trees and plants every day or night and shake them hard and the hose them as a final measure. It has saved my plants and trees. As for my huge oak, it is so big and covered with them and so far, it has managed to survive this onslaught. Good luck! Peace out.

    Reply
  12. Linda

    While this is not a perfect solution nor something that can be done on a large scale – I was able to save my 3 blueberry bushes this year by coating them with diatomaceous earth. They are still leafy whereas this time last year they were nearly naked stems. I’m not sure if I’ll see any berries again this year, but I’m hopeful. I have a large bag of good-grade diatomaceous earth and use a powder spritzer to apply. In late fall, I’m going to try wrapping the trunks of my crab apple and weeping cherry to try to cut down on the number eggs laid on each of those.

    Reply
  13. Kathleen Forsythe

    They’re also eating some of my leafy perennials. What can I spray on them to protect them?

    Reply
  14. Kath

    As far as “native trees” are concerned, we have a 300-year-old oak that has been devastated! Hope it makes it through this, the second year of infestation!

    Reply
  15. virginia

    I suspect Audubon does not want to promote any type of corrective action to protect the trees that will threaten BIRDS that eat the worms. From UMASS Amherst:
    The Solutions:

    Bacillus thuringiensis, commonly known as B.t., is sold under many different trade names and is quite effective against the younger caterpillars. This product is relatively “safe” when compared to traditional chemicals.

    Reply
  16. Don

    My entire crab apple tree and the neighboring red maple next to it are LITERALLY…covered with tiny green caterpillars and an unbelievable amount of webbing the tiny pillars are using to get down to the ground. One can’t even walk under it without getting encased in what feels like spider webs! Is this normal? Or would this be classified an infestation?

    Reply
    1. Hillary

      Unfortunately, this year it is common and it is an infestation. The winter moth caterpillars use silk, similar to what a spider uses to spin their’ web, to move from one tree to another. The little black pellets are the fecal matter; sometimes there are so many caterpillars munching away one can hear the little pellets hitting the other leaves before they hit the ground. By the beginning of June the caterpillars should be through feeding and starting to pupate until mid-November when they break out and start to fly around the lights and begin to mate. The whole lifecycle starts over again.

      Reply
  17. Saunie

    Are these found in Southern California (San Diego County)?
    If so, i am finding them on my sweet pea seedlings

    Reply
    1. Hillary

      The winter moth is on the west coast but is primarily in the states of Washington and Oregon. They generally feed on trees maples, oaks, cherries, crab apples, and blueberries.

      Reply
      1. Linda

        I’m in a suburb West of Boston, MA and we have also been experiencing infestation for the last 2 or 3 years.

        Reply
  18. Bob Tess

    Brilliant! So helpful. I’ll just cut down all my orchard trees and small fruit shrubs and plant native vegetation. Thank you! I knew I could count on you for a good solution.

    Reply
    1. Alex Avier

      My wife and I just completed the demolition of all of the plants and trees in our yard! It worked! Now we’re thinking of covering the grounds with blacktop! No more bugs in our lives! No more plants either! Just blacktop!
      Thank you!

      Reply
  19. Lesa

    For the last two years my Elm trees & Mountain Laurels have been striped by these worms. They even got into my a/c unit & blew out the master board. Is there any organic sprays I can use to protect my trees?

    Reply
  20. Kevin

    I just received an offer from my lawn company to spray horticultural oil on my trees to prevent damage from the winter moths. Would this be effective?

    Reply
    1. Hillary

      From a Mass Audubon scientist: Horticultural oil is used to control winter moth, as well as woolly hemlock adelgid and other insects. Its mode of action is smothering of egg masses. We have used horticultural oil to control in hemlock woolly adelgid on hemlocks in the past. Timing of the treatment so that it occurs prior to the eggs hatching is important.

      Reply
  21. Phyllis

    The moth loves to eat my monada s I plant to attract butterfly’s . What do I do to get rid of them

    Reply
  22. Linda

    Wondering if diatomaceous earth will have any affect on the caterpillars? If the tree trunks are dusted with this powder, maybe it will slow them down a bit as they begin to emerge in the spring? I have a crab apple, weeping cherry and blueberry bushes are that have been getting devastated for the past couple years. So far they have rebounded, but I’m not getting that much fruit.

    Reply
    1. Chris McClain

      They have eaten my meadow rue, but nothing else that I can see. Will the rue come back? It unfortunately got shaded by some bushes this year. I will keep those cut back in the future. Ths is right next to a wild mixed tree area.

      Reply
  23. Wayne Rogers

    How long does this leaf eating continue. I’m from RI, and all my trees have been attacked, I’d say it started about Mid May, & now it’s almost the end of May.
    Can I expect this to end soon?

    Reply
    1. Hillary

      Yes, it should be ending soon. The damage this year has been worse than years past and fortunately we have had a cool spring. A warm spring would have put more stress on the moth eaten leaves. If we continue to have a cool, rainy spring most trees should recover and send out a new flush of leaves.

      Reply
  24. Kevin Skelly

    I have 3 very large oaks in my back yard and they are completely defoliated. These are mature 30 – 40 foot trees and are native. I am very concerned they may not handle the stress. The caterpillars have left an enormous anount of waste all over the deck and yard ( looks like black pepper ). It doesn’t look like our harsh winter had any impact on these invasive insects.

    Reply
  25. Michele Overton

    We have a beautiful 20+ year old cherry blossom tree that did not produce the usual blooms. As we looked closer, we saw the holes in the leaves and the tiny green buggers all over it. What should we do? Will the tree survive and bloom next year? Do we need a professional to spray it or something? I would certaintly hate to loose it. Appreciate some feedback.
    Thanks

    Reply
    1. Hillary

      As Kathi notes in the post:

      “Most trees can handle a year of this leaf eating if there are not other forms of stress such as drought, insect infestation, or too much sun or shade depending on the tree. Often, they can send out a second flush of leaves.”

      and

      “Sure there are sprays that can eradicate them. But, keep in mind they are not selective. The spray that kills the caterpillar stage of the winter moth also kills all of the butterflies in their caterpillar stage.”

      Reply
  26. Russ Cohen

    I for one am hoping that this past cold winter we all endured will result in less winter moth caterpillars.

    The main tree in our yard they seem to like is our dwarf sour cherry tree. Fortunately the tree is small enough that I can inspect it thoroughly once/day in a few minutes, and then I just squish any winter moth caterpillars I see. That usually results in a good cherry crop.

    Reply

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