The Fall Webworm Moth, scientifically known as Hyphantria cunea, is a common pest found throughout the United States and southern Canada. These native North American insects are known for their feeding habits on a wide variety of shade, fruit, and deciduous ornamental trees, with some preferred hosts including American elm, birch, hickory, and some maples Wisconsin Horticulture.
In early spring, adult moths emerge, and females lay egg masses on the underside of leaves. As the caterpillars hatch and grow, they create conspicuous white webs around the leaves Clemson Home & Garden Information Center. These webs expand over tree branches throughout the summer and are an easily recognizable sign of their presence. The caterpillars are not only interesting to observe due to their defensive thrashing behavior when disturbed, but it is also essential to understand their impact on tree health and proper management techniques Purdue Extension Forestry.
Fall Webworm Moth Identification
The Fall Webworm Moth, also known as the mulberry moth, belongs to the Erebidae family. This species is particularly active during the warmer months, typically between April and September. The moth exhibits some subtle variations in appearance depending on its location:
- Northern populations: Usually pure white, creating a bright appearance.
- Southern populations: White with dark wing spots.
The wingspan of these moths ranges from 25 to 40 millimeters, and they feature a hairy body.
Once the Fall Webworm Moth lays its eggs, caterpillars emerge and begin constructing their webbed nests. These caterpillars showcase distinct attributes:
- Color: Ranging from yellow to light green.
- Feeding habits: They feed on the surface of leaves during their early stages, progressing to devour entire leaves as they mature.
- Webbing: They create large tents around the leaves they consume.
Similar caterpillar species, like the Eastern Tent Caterpillar, also form tents around leaves, but the Fall Webworm is known to create significantly more extensive webbing. With their distinct characteristics, identifying Fall Webworm Moths and their caterpillars becomes simpler.
Life Cycle and Reproduction
- Laid on the underside of leaves
- Moths lay up to 1,500 eggs
In spring, the adult Fall Webworm Moth lays eggs on the underside of leaves. A single female can lay nearly 1,500 eggs, which are covered with white hairs from her abdomen.
- Caterpillars are pale green with long hairs
- Feeding on leaves
After hatching from the eggs, the larvae (caterpillars) start by feeding on the leaf’s surface. As they mature, the larvae, which are pale green with long hairs, devour entire leaves.
- Overwinter in cocoons
- Found in mulch or soil
When fully grown, caterpillars transform into pupae within cocoons. The pupae overwinter in mulch or soil, remaining dormant until the following spring.
- Appear in late June and July
- Multibrooded species; moths seen from early April to September
Adult Fall Webworm Moths, which are mostly white, emerge from their cocoons in late June or early July. The moths are active and reproduce throughout the season, making them a multibrooded species. The moths can be found from early April until September.
Comparison Table: Fall Webworm Moth Life Stages
|Life Stage||Characteristics||Time of Year|
|Eggs||Laid on underside of leaves, covered in white hairs||Spring|
|Larvae||Pale green, long hairs, feed on leaves||Spring to Summer|
|Pupa||Overwinter in cocoons, found in mulch or soil||Fall to Winter|
|Adult Moth||White, multibrooded, active from April to September||Summer to Fall|
Habitat and Distribution
The Fall Webworm Moth, belonging to the family Erebidae, is native to North America, specifically the eastern regions. Its distribution extends from the US up to southern Canada, where it reaches its northern limit at latitudes between 50-55°1. In these areas, it is a common pest causing defoliation in deciduous trees and shrubs2.
- Native to Eastern North America
- Range extends to Southern Canada
The Fall Webworm Moth was introduced in Europe in the 1940s, first recorded in Yugoslavia3. Since then, it has spread across the continent, expanding its habitat and distribution in various European countries.
- Introduced in the 1940s
- Spread throughout Europe
In Asia, the Fall Webworm Moth has also established its presence. It has been reported in countries like China, North Korea, and Japan. The moth continues to be a concern for both forest health and agriculture in these regions.
- Present in China, North Korea, Japan
- Affects forestry and agriculture
Comparison Table: Fall Webworm Moth Distribution
|Region||Native/Introduced||Year of Introduction|
Host Trees and Damage
Types of Trees
Fall Webworm Moths (Hyphantria cunea) are known to infest more than 100 species of deciduous forest and shade trees. Here’s a list of some common host trees:
Their preference also includes fruit trees like cherry, apple, and pecan, as well as ornamental trees such as black cherry, American elm, and some shrubs.
Signs of Infestation
Fall webworms leave a few telltale signs on the trees they infest.
Webs on branches: These small, pale-yellow caterpillars create large, conspicuous white webs on tree branches that grow over the course of the summer.
Damaged foliage: As the caterpillars feed, they consume large amounts of foliage leaving behind skeletonized leaves.
Here’s a comparison table of different tree types concerning fall webworm susceptibility:
|Tree Type||Fall Webworm Susceptibility|
It is essential to observe trees for these signs to ensure timely management and control measures. Although the damage inflicted by fall webworms may not directly kill the tree, severe defoliation weakens the tree’s defense against other pests and diseases.
Control and Management
Many predators help keep fall webworm populations in check. Some examples include:
- Birds, which feed on the caterpillars
- Parasitic insects, such as wasps and flies
- Predatory insects, like ants and beetles
Practicing good cultural control can reduce the impact of fall webworms on your plants. Key points for cultural control are:
- Promptly remove and destroy webbed branches
- Encourage natural predators by maintaining diverse plantings
In cases of light infestations, pruning infested branches or using a forked stick to remove webs can help.
Certain insecticides can be used to manage fall webworms, including:
- Bacillus thuringiensis (Bt)
It’s important to apply insecticides when caterpillars are young, and focus on the undersides of leaves where eggs are laid.
|Bacillus thuringiensis (Bt)||Safe for beneficial insects||Slow-acting|
Keep in mind that using insecticides may harm beneficial insects, so it’s best to use them only when necessary.
Fall Webworm Moth vs Eastern Tent Caterpillar
Fall webworm moth (Hyphantria cunea) and Eastern tent caterpillar (Malacosoma americanum) are two different species with distinct visual differences. Fall webworm caterpillars have:
- Light-colored bodies with black and yellow markings
- Long hairs, or tubercles, that protrude from their bodies
On the other hand, Eastern tent caterpillars have:
- Dark-colored bodies with a white stripe along their backs
- Shorter hairs and fewer tubercles
These two species also exhibit different behaviors. Fall webworms:
- Create large silk tents at the ends of branches
- Are gregarious, feeding and living within their silk tents in large groups
- Feed on a wide variety of deciduous trees, including more than 120 different species
Comparatively, Eastern tent caterpillars:
- Build their silk tents in the crotches and forks of branches, rather than at the tips
- Also feed in groups, but are more conspicuous as they move across branches to find new feeding sites
- Preferentially feed on crabapple, hawthorn, and flowering cherry trees
|Feature||Fall Webworm Moth||Eastern Tent Caterpillar|
|Appearance||Light-colored with black and yellow markings, long hairs||Dark-colored with a white stripe, shorter hairs|
|Silk Tent Location||Ends of branches||Crotches and forks of branches|
|Feeding Preferences||Over 120 deciduous tree species||Crabapple, hawthorn, and flowering cherry trees|
In conclusion, understanding the visual and behavioral differences between fall webworm moths and Eastern tent caterpillars can help in identifying and managing these two species effectively.
Impact on Forestry and Ecosystem
The fall webworm moth is a known pest that has a significant impact on forestry and ecosystems. With their larvae feeding on more than 100 species of deciduous forest and shade trees, the infestation causes stress for tree species, including fruit trees such as apple.
To better understand the fall webworm moth, it is essential to look at the life stages. The larvae, or caterpillars, can have two appearances:
- Satin white with dark stripes and spots
- Dull bluish-black without yellow markings
Their main distinction is that both types have very hairy bodies. These larvae feed on tree leaves and build large, conspicuous web-like nests during late summer, which can be noticed in various tree species.
The fall webworm can have multiple generations, making infestations challenging to control. When allowed to thrive, it can cause significant damage to the trees, including complete defoliation. This increases the trees’ stress and negatively impacts the overall health of the forest ecosystem.
It is not just the local ecosystem that suffers due to fall webworm moths. The species is considered an invasive pest in Europe and Asia, affecting both ornamental trees and agriculture crops. This spread to other regions causes further strain on global ecosystems and forestry.
One way to manage fall webworm infestations is the introduction of parasitoids. These insects can help to control the pest population in a natural manner, without the need for chemical treatments.
In conclusion, the fall webworm moth’s impact on forestry and ecosystems cannot be underestimated. Damage caused by their larvae infestation can weaken individual trees, affect the health of forests, and even disrupt agricultural production. Implementing management strategies, such as parasitoid introduction, can help to mitigate these negative impacts and maintain a more balanced ecosystem.
Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.
Letter 1 – Fall Webworm Moth
April 10, 2017 3:52 am
We just moved out here and curious who these guys are.
Based on this BugGuide image, we are confident that your spotted moth is a Fall Webworm Moth, Hyphantria cunea. According to BugGuide: ” wings either all white (in northern and some southern individuals) or sparsely to heavily marked with dark grayish-brown to black spots (in many southern individuals); spots rectangular or wedge-shaped, arranged loosely in rows in basal half of wing, and in either a V-shape or more-or-less random arrangement in distal half; ventral side of prothorax and femur of foreleg with orange hairs; hindwing either all white or with one or two black spots” BugGuide also notes: “Larvae feed on foliage throughout their development, and secrete silk which they spin into small webs. As they grow, they enlarge the webs, which can sometimes enclose the entire tree. Even severe infestations have little impact on trees because the damage occurs near the end of the annual growing season. Except in the case of ornamental trees, control is seldom necessary because the damage is generally of aesthetic rather than economic importance.” You should expect to see the webs formed by the caterpillars in late summer.
Letter 2 – Fall Webworm Moth
Geographic location of the bug: North Carolina
Time: 03:22 PM EDT
Your letter to the bugman: I see a lot of moths in rural NC but have yet to see one like this one and was curious as to what this moth is called.
How you want your letter signed: Angelique Sachak
There are many similar looking white Tiger Moths with black markings that are native to your region, especially those in the subtribe Spilosomina, which you can see on BugGuide, but the antennae and the coloration of the front legs on your individual leads us to believe this is a Fall Webworm Moth, Hyphantria cunea. According to BugGuide: “wings either all white (in northern and some southern individuals) or sparsely to heavily marked with dark grayish-brown to black spots (in many southern individuals); spots rectangular or wedge-shaped, arranged loosely in rows in basal half of wing, and in either a V-shape or more-or-less random arrangement in distal half; ventral side of prothorax and femur of foreleg with orange hairs; hindwing either all white or with one or two black spots.”
Letter 3 – Fall Webworm, we believe
I found these strange webs and what look like egg sacs in the trees in the garden. I was just wondering if you would be able to tell me what spider has made them as i’ve never seen anything like it before. The webs that i think contain egg sacs are about the size of a tennis ball.
Thanks, Zoe Lehan
You did not provide us with a location for your images. Your images are small files lacking in clarity and detail, but we suspect these are the nests of the Fall Webworm, and not the Eastern Tent Caterpillar. According to BugGuide, with the Eastern Tent Caterpillar, Malacosoma americanum: “Tents appear in early spring, and caterpillars are seen until early summer.” By contrast, the Fall Webworm, Hyphantria cunea, according to BugGuide builds: “Weblike tents in branch tips where clusters of caterpillars strip foliage (by contrast, eastern tent caterpillar nests are built in tree crotches).” BugGuide also indicates: “Caterpillars are found June to September or October in the north; May to October in the south. Larva are most often noticed when they reach final instar and wander out of their home trees to find a place to pupate.”
Letter 4 – Fall Webworms
Location: Northern Kentucky, near Cincinnati, OH
August 4, 2010 10:12 am
I’ve taken some photos that I believe are of fall webworms. This appeared almost overnight. The catepillars are still very small, but they look to be the white/cream black-headed variety. They’re so beautifully furry that it’s almost impossible to see where they end and the web begins.
I liked the way the sun was shining on the web and the catepillars, making them almost glow.
Thought I’d submit them to you since I couldn’t find many shots of these guys on your site and thought you may be interested in them.
Hi again Ragdoll,
YOur stunning photographs of Fall Webworms, Hyphantria cunea, are a welcome addition to our website.
Glad you liked the pics. What a difference a day makes…24 little hours…
Today my caterpillars think they are all grown up. They are fully white and luxuriantly fuzzy with a lovely green stripe down their backs. They’re bursting out of their web and looking for place to call their own to feast before entering the pupae stage on their way to becoming lovely white moths.
*sigh* They grow up so fast….
Letter 5 – Fall Webworms
Subject: Fall Webworms
Location: near Villa Marie, Pennsylvania
August 12, 2013
Though there are numerous requests in our inbox, from the past few days as well as the accumulation of answered mail during our 2 1/2 weeks away from the office, we still feel compelled to post a few of our photos from the Ohio/Pennsylvania border area. Fall Webworms, Hyphantria cunea, create huge web nests to protect the caterpillars as they are developing. These webs are found on many species of trees in the Northeast. According to BugGuide they feed upon: “About 120 species of hardwood trees have been recorded as larval hosts
in the north, common hosts include alder, apple, ash, birch, Box-Elder (Acer negundo), cherry, elm, mulberry, poplar, willow
in the south, common hosts include ash, hickory, maple, mulberry, oak, pecan, poplar, redbud, sweetgum, walnut, willow; preferences for different host plant species appear to be regional and seasonal.”
This large web was on a nut tree. Upon closer inspection, tiny caterpillars could be spotted. They thrash about when their web is disturbed.
Letter 6 – Fall Webworms
Subject: What is it?
Location: Jackson, Wyoming
June 19, 2016 4:57 pm
Can you identify this?
Signature: Don’t care
These are Fall Webworms, Hyphantria cunea. According to BugGuide: “Weblike tents in branch tips where clusters of caterpillars strip foliage (by contrast, eastern tent caterpillar nests are built in tree crotches)” and “Larvae feed on foliage throughout their development, and secrete silk which they spin into small webs. As they grow, they enlarge the webs, which can sometimes enclose the entire tree. Even severe infestations have little impact on trees because the damage occurs near the end of the annual growing season. Except in the case of ornamental trees, control is seldom necessary because the damage is generally of aesthetic rather than economic importance.” BugGuide also notes: “About 120 species of hardwood trees have been recorded as larval hosts in the north, common hosts include alder, apple, ash, birch, Box-Elder (Acer negundo), cherry, elm, mulberry, poplar, willow in the south, common hosts include ash, hickory, maple, mulberry, oak, pecan, poplar, redbud, sweetgum, walnut, willow; preferences for different host plant species appear to be regional and seasonal.”
Letter 7 – Fall Webworms
Subject: Large cocoon like spider web
Geographic location of the bug: Baldwin, Maryland
Time: 01:42 PM EDT
Your letter to the bugman: I was wondering if you could tell me what kind of cocoon or web this is and what is inside it?
How you want your letter signed: Thank you, Michele
This appears to be a web full of Fall Webworms, Hyphantria cunea. Here is a BugGuide image of the caterpillars that are inside the web. According to BugGuide: “About 120 species of hardwood trees have been recorded as larval hosts. In the north, common hosts include alder, apple, ash, birch, Box-Elder (Acer negundo), cherry, elm, mulberry, poplar, willow. In the south, common hosts include ash, hickory, maple, mulberry, oak, pecan, poplar, redbud, sweetgum, walnut, willow; preferences for different host plant species appear to be regional and seasonal.”
Letter 8 – Fall Webworms
Can you help?
Every year in August in Michigan( all through michigan), I see this web like mass in trees. I asked the locals, they had no clue what they were, they didn’t even notice them. Do you know what it is?
This is a Fall Webworm, Hyphantria cunea, nest. In the fall, these social caterpillars can build enormous webs that cover the leaves. Here is a site with more information.
Letter 9 – Mating Fall Cankerworm Moths
Subject: Wingless moth..?
November 27, 2015 7:13 am
I found these 2 moths seemingly mating on top of my shoe last night !! I always call these “winter moths” since they come out in December but I would like more information on maybe why this ones wings are gone? Is one sex flightless? Or did something happen to it? – sorry about the photo quality, my camera would not focus on them.
It is unfortunate that the point of focus is your shoelace, and not the moths, but we believe these are mating Winter Moths, Operophtera brumata, an introduced species with wingless females and winged males, and the males resemble the individual in your image based on this BugGuide image. The general appearance of the moths, the time of the sighting and your location are all consistent with what we know about Winter Moths. According to BugGuide: “Native to Europe, introduced to Northeast and Pacific Northwest, pest species in areas such as Boston. Established in the NW since the 1970s” and “adult males seen October to February and often attracted to lights” We should point out that other species in the family Geometridae also have flightless female moths, including the Fall Cankerworm Moth, Alsophila pometaria. According to BugGuide: “The females are wingless and stout-bodied, with the body banded dark and pale gray.” We are amused that your name for these moths is the approved common name.