How Do Woolly Bear Caterpillars Predict Winter? The Secret Behind Their Furry Forecast

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Woolly bear caterpillars have long been associated with predicting the severity of the upcoming winter. These fascinating creatures are believed to hold clues about winter conditions based on the colors and patterns of their thick, fuzzy coats.

The woolly bear is actually the larva of the Isabella tiger moth, and its body is made up of 13 segments that are either rusty brown or black in color. Folklore suggests that a wider rusty brown band in the middle indicates a milder winter, while more black suggests a harsher and colder season. However, scientists argue that the variations in color bands are more related to the age and growth of the caterpillar, rather than being a reliable weather prediction. Nonetheless, this traditional belief persists and adds an interesting folklore aspect to these engaging creatures.

Woolly Bear Caterpillar Basics

Appearance and Biology

Woolly bear caterpillars are known for their distinctive fuzzy appearance. They have black setae (hair-like structures) at both ends, and reddish-brown setae in the middle. As they grow older, the black segments become smaller, allowing more of the reddish-brown to show.

Isabella Tiger Moth

The woolly bear caterpillar is the larval form of the Isabella tiger moth (Pyrrharctia isabella). The adult moth itself is somewhat unremarkable in appearance, with yellow-brown wings and a series of small black dots. The hind wings are slightly paler and pinkish.

Habitat

The woolly bear caterpillar is found throughout the U.S., Mexico, and southern Canada. Their habitat consists mainly of areas with ample vegetation for feeding, such as meadows, gardens, and forests.

Comparison between Woolly Bear Caterpillar and Isabella Tiger Moth:

Feature Woolly Bear Caterpillar Isabella Tiger Moth
Appearance Fuzzy, black and red-brown Yellow-brown wings, black dots
Development stage Larvae Adult
Activity Crawling on vegetation Flying, attracted to lights at night
Habitat Meadows, gardens, forests Same as caterpillar’s habitat

Pros and Cons of Woolly Bear Caterpillars as Winter Predictors:

Pros:

  • Easy to observe and find due to their distinctive look and habitats
  • An interesting and engaging way for people to learn about nature and insects

Cons:

  • Scientifically unproven method in determining winter severity
  • Inaccurate predictions can mislead people regarding winter preparations

Folklore and Winter Predictions

Origins

Woolly bear caterpillars, the larval form of the Isabella tiger moth (Pyrrharctia isabella), have been part of American folklore for predicting winter weather. The belief dates back to when people relied on nature’s signs for forecasting.

Reading the Bands

These caterpillars have 13 segments with either rusty brown or black coloration. The folklore suggests that:

  • Wider brown bands indicate a milder winter
  • Wider black bands signal a colder, harsher winter

Accuracy of Predictions

Though woolly bears are embraced by many, the scientific consensus on their ability to predict winter is less confident. Factors influencing their band colors include:

  • Age
  • Species
  • Environmental factors throughout their lives

For example:

  • Young caterpillars have mostly black bands, which turn brown as they age
  • Geographic variations also exist among woolly bears, influencing coloration

Pros:

  • Charming folklore
  • Fun conversations about the winter season

Cons:

  • Not scientifically proven
  • Many factors influence the color of the bands

Comparison table:

Folklore Prediction Scientific Viewpoint
Wider brown bands indicate a milder winter Band color influenced by age, species, and environmental factors
Wider black bands signal a colder, harsher winter Not a reliable method for predicting winter weather

In summary, while woolly bear caterpillars have been part of folklore for predicting winter weather, their accuracy remains scientifically unproven, and their colorations are influenced by a variety of factors.

Scientific Explanations

Growing and Molting

Woolly bear caterpillars go through several stages of growth and molting throughout their life. During the growing season, they feed on leaves and other vegetation. They molt multiple times, gradually changing the coloration of their segments.

  • Molting helps caterpillars grow larger
  • Coloration changes may be related to temperature and age

Role of Temperature and Setae

The appearance of woolly bear caterpillars can be influenced by temperature and their age. The longer a caterpillar has been feeding and growing, the more brown bands it will have, and shorter periods of feeding may result in more black bands.

  • Temperature impacts their growth rate
  • Age affects the proportion of brown and black setae

Cryoprotectant and Hibernation

Woolly bear caterpillars are known for their ability to hibernate during the winter months. They produce cryoprotectants like glycerol and other chemicals in their hemolymph, which prevents their tissues from freezing.

  • Glycerol acts as an antifreeze for their body
  • Hemolymph carries nutrients and cryoprotectant chemicals
Feature Woolly Bear Caterpillars
Growing Season Impact Feed on leaves, molt
Temperature Influence Growth rate, coloration
Hibernation Ability Cryoprotectants

Pros of woolly bear caterpillar hibernation:

  • Ability to survive harsh winter conditions
  • Cryoprotectant chemicals protect tissues from freezing

Cons of woolly bear caterpillar hibernation:

  • Longer development time due to periods of inactivity
  • Dependence on sufficient food supply before hibernation

Woolly Bear Festivals

Vermilion, Ohio

In North America, the annual Woolly Bear Festival takes place in Vermilion, Ohio. Held every October, this event celebrates the woolly bear caterpillar’s alleged ability to predict the upcoming winter weather. Some highlights of the festival include:

  • Woolly bear costume contests
  • Races featuring the woolly worms
  • Various entertainment and food vendors

Banner Elk, North Carolina

Another popular Woolly Worm Festival occurs in Banner Elk, North Carolina, also held annually in October. This festival features:

  • Woolly worm races with cash prizes
  • Live music, food, and craft vendors
  • Family-friendly activities and entertainment
Vermilion, Ohio Festival Banner Elk, North Carolina Festival
October October
Costume Contests Woolly Worm Races with Prizes
Woolly Worm Races Live Music, Food, and Crafts
Entertainment & Food Family-Friendly Activities

Alternative Winter Prediction Methods

Punxsutawney Phil Groundhog Day

One popular and entertaining method of winter prediction in the United States is Punxsutawney Phil Groundhog Day. On February 2, a groundhog named Phil emerges from his burrow.

  • If Phil sees his shadow, winter will continue for six more weeks.
  • If he doesn’t, spring will come early.

However, this tradition has no scientific basis.

National Weather Service Forecasts

National Weather Service (NWS) provides winter forecasts based on data and models.

  • More accurate than folklore-based predictions
  • Covers North Carolina, Canada, and the entire United States
Prediction Method Accuracy Location Coverage
Groundhog Day Low US
National Weather Service High US and Canada

Traditional Indicators

Some people rely on traditional indicators for winter predictions, such as:

  • Woolly bear caterpillars: based on their color patterns
  • Animal behavior: squirrels gathering more nuts, birds migrating early

Keep in mind that these methods are not scientifically proven, unlike NWS forecasts.

Reader Emails

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 – Tiger Moth: Grammia species

 

what’s this moth?
Hi,
You very kindly identified a moth for me yesterday, and I already have another one! This one looks similar to the vine moth shown in pictures on your site, but the vine moth was described as having a southern distribution, whereas I took this photo in Chetwynd, British Columbia (in June). Also, the markings are a bit different. Any idea what it is?
Thanks!
Melanie

Hi again Melanie,
According to BugGuide, there are 28 species of Tiger Moths in the genus Grammia in North America. We can’t even begin to identify the species, so we hope the genus will do.

Letter 2 – Tiger Moth, genus Haploa

 

Beautiful Clymene moth?
Hello fellow insect lovers,
I just wanted to start by saying that your site has really educated my family on the types of insects we have outside our home. I understand your "swamped", but now I have a need to know exactly what im looking at, because of you guys. So…what kind of moth is this? Some type of Clymene? Were up in Burlington Vermont.
Thanks
Bern

Hi Bern,
We don’t know what species this is, but it is definitely a Tiger Moth in the genus Haploa, a close relative of the Clymene Moth, but not Haploa clymene.

Letter 3 – Tiger Moth in genus Grammia

 

ID of moth
Having trouble IDing this moth we found during the Shenandoah NP July 4 Butterfly Count. We are interested in everything so would like to know what kind of moth this is. Thanks,
Glenn Koppel
Centreville, VA

Hi George,
This is a Tiger Moth in the genus Grammia, probably the Parthenice Tiger Moth, Grammia parthenice, or the Virgin Tiger Moth, Grammia virgo. Seeing the underwings would have helped with a more exact identification.

Letter 4 – Tiger Moth from Seattle with a very limited range is Lophocampa roseata

 

Red Moth by Seattle
Hi there,
I found your website and I have enjoyed learning from it. I wondered if you knew what type of moth this is, it has been hanging around our place just north of Seattle the last few days. It is quite colorful, I am having trouble finding an exact match online. Even a short email leading me in the right direction would be very helpful sometime, it sounds like you get tons of email so thanks if you do get to this one. I’ve never seen a moth like this by our house before, it was really striking. Perhaps I just never noticed them, but who knows.
Mark

Hi Mark,
We don’t immediately recognize your moth, and a brief search of possibilities has not provided an answer. We have put in a request to Arctiid expert Julian Donahue and are eagerly awaiting his response. We had hoped to get that response to avoid updating this entry. Interestingly, the pattern and coloration resembles the Royal Walnut Moth, but we are confident that your moth and the Royal Walnut Moth are not closely related. We believe your moth is a Tiger Moth, an Arctiid, but are uncertain of the species. How large was this moth????

Hello, thanks for writing back to me so quickly. It wasn’t very large actually, about the size of a quarter. It didn’t mind me getting my digital camera up very close for a few pictures, and hung around for about 2 days, but I think it has departed. I’ve never seen a moth with those sorts of colors around our area, most of the ones attracted to our porch lights are varying shades of white, brown, grey, etc. It stood out immediately.

Identification: courtesy of Julian Donahue
This is the tiger moth Lophocampa roseata. According to the distribution map at http://www.butterfliesandmoths.org/species?l=3774 it only occurs in the Seattle area. I haven’t checked the LACM collection to see if we have additional records.
Julian

Wow Julian,
Thank you so much. We feel so lucky to have been provided with an image of a Tiger Moth with such a limited range.

Letter 5 – Flannel Moth from Costa Rica

 

Moth, fly, or?
Sun, Nov 16, 2008 at 4:37 PM
Hi, again! I love this site and Bug Guide. The two photos below were taken on my patio on an old white plastic table (for color interpretation) and are of a flying insect with white wings and thorax and tiny tufts of red hairs forming a kind of pattern. I have seen the same type of insect with black tufts instead of red. I live at about 1100 meters on the Pacific slopes of a mountain range in southeastern Costa Rica. The largest nearby city is San Vito. These particular insects seem to be more common during the dry season.
Mary Thorman
Costa Rica

Tiger Moth from Costa Rica
Tiger Moth from Costa Rica

Hi Mary,
We believe this is a Tiger Moth and we are going to contact an expert in the Arctiidae, Julian Donahue, for assistance with the species identification.

Sorry–it’s a megalopygid. Common, but I don’t recall the generic name at the moment.
Julian

Correction: Tue, Nov 18, 2008 at 10:46 AM
Hello Bugman:
I believe this is a moth in the Family Megalopygidae (Flannel Moths), in the Genus Trosia. Trosia is a very abundant genus and they all look quite similar, but Trosia fallax appears to be a very close match. Cheers.
Karl

Letter 6 – Cream Spot Tiger Moth from Turkey

 

beautiful moth from southern Turkey
September 17, 2009
Hello! I took this picture of a moth on the hills above the southern coast of Turkey. I was told it was native to that part of Turkey and one island of Greece and nowhere else. I use it in the masthead of my blog, so would love to be able to name the species.
Hope you can help – thanks,
Cath
southern Turkey – near Eşen / Fethiye

Tiger Moth
Cream Spot Tiger Moth

Hi Cath,
This is a Tiger Moth in the family Arctiidae.  We will contact Julian Donahue, a lepidopterist who specializes in the family, to see if he can provide a species identification.

Julian Donahue responds
It’s the Cream-spot Tiger (Arctia villica); widespread, from southern England through Europe and western Asia and North Africa.
Julian P. Donahue

Letter 7 – Leopard Moth from France

 

Moth?
Location: Le Chautay, France
May 13, 2012 4:59 am
Dear Bugman,
my aunt found this beautiful creature during last summer on the ground – i was wondering if you could identify it for me.
Signature: Cassia

Leopard Moth from France

Dear Cassia,
This is a Tiger Moth, and we cannot find any photos of French or European species that look similar, however, both the wing markings and body markings are remarkably similar to a North American species
Hypercompe scribonia, known as the Giant Leopard Moth which is pictured on BugGuide.

Correction Courtesy of Karl:  Leopard Moth
Hi Daniel and Cassia:
It probably is a Leopard Moth, but not the North American variety. The European species of Leopard Moth, or Wood Leopard Moth (Zeuzera pyrina), is actually a Carpenter Moth in the family Cossidae.  The larvae are stem borers and apparently can take up to three years to develop into adults. They are considered a minor pest on fruit trees. There is a fair amount of online information about the species, including this page from the “Interactive Agricultural Ecological Atlas of Russia and Neighboring Countries”.  I don’t know if the North American species Hypercompe scribonia has made it to Europe, but Z. pyrina has been established in the northeastern USA since the late 19th century. Regards.  Karl

Wow, thanks Karl,
This Leopard Moth looks so much like the Giant Leopard Moth.

Letter 8 – Tiger Moth from Zambia

 

Subject: Insect
Location: Southern Zambia, Africa, on the Zambezi River
August 15, 2012 4:28 pm
While cruising on the Zambezi River in Zambia just before sun-down in late April of this year, the bug depicted landed on our table cloth. Is there a chance that you could identify this bug?
Signature: Joe Weber

Tiger Moth from Zambia

Dear Joe Weber,
We believe this is a Tiger Moth in the subfamily Euchromiina, a group that contains many members that mimic wasps for protection.  We will try to determine a species  for you, though we may have to enlist the help of Arctiid expert Julian Donahue. Some North American examples of this family can be found on BugGuide.  Further research reveals it is likely the Heady Maiden,
Amata cerbera or Amata aliciabased on photos posted to ISpot and African Moths.  We are postdating your letter to go live on Saturday during our brief absence from the office.

Letter 9 – Tiger Moth from Costa Rica: Amastus aconia

 

Subject: Night butterfly or moth
Location: costa rica
March 24, 2013 2:21 pm
a beautifull insect from Peninsula de Osa
Signature: fred from belgium

Tiger Moth:  Amastus aconia
Tiger Moth: Amastus aconia

Hi Fred,
We took a brief break from gardening to answer the phone and then checked the computer, and we got sucked into trying to identify this lovely Tiger Moth.  We
found an identification request on InsectNet where it is identified as Amastus aconia.  There is a link to a live specimen on TropicLeps.  Now we have to weed the vegetable patch and get the tomato, jalapeño and basil plants in the ground.

Letter 10 – Tiger Moth from Indonesia

 

Subject: Indonesian moth
Location: Indonesia
January 4, 2015 11:12 am
This pretty moth was in our bathroom at Wakatobi Dive Resort, on a small island off of Tomia (or Tomea), which is a slightly larger island off of southeast Sulawesi in Indonesia, in late December. Thanks for the help!
Signature: L. Sanford

Heliotrope Moth
Heliotrope Moth

Dear L. Sanford,
This diurnal Tiger Moth is a Heliotrope Moth,
Utetheisa pulchelloides, which we identified on this blog from Indonesia.  The same species is called a Crimson Speckled Footman on the Cook Islands Biodiversity site.  A very similar looking moth is identified as Utetheisa lotrix on The Papua Insects Foundation site.

Daniel,
Thanks for the id! That is exactly the moth I saw. One question though: I sent in two id requests at about the same time, and you replied to my second request with the id of the moth in the first. Were you able to check on the second moth? I totally understand if you don’t have the time or resources for the second, I just wondered if there was a mix-up and you missed my second picture. (Next time I will send both requests in the same message to avoid the confusion.)
Thanks again for your help!
Lindsay

Hi Lindsay,
You should limit submissions to a single species.  I have not had time to look at the second moth.  Also, you did not initiate with a new form, hence stacking the two requests together.

Letter 11 – Tiger Moth from Greece

 

Subject: moth
Location: Kalamaki, Zakynthos, Greece
October 13, 2015 11:03 pm
I found it in my room in Zakynthos, Greece
Signature: ?

Tiger Moth
Tiger Moth

This is a Tiger Moth in the subfamily Arctiinae.  We have not been able to determine the species as this time.

Letter 12 – Tiger Moth from Colombia: Histioea meldolae

 

Subject: Beautiful… Moth?
Location: 7°53’11.6″N 72°29’46.7″W
February 24, 2016 10:47 am
I was traveling in Cucuta, Colombia and noticed this interesting looking insect in the elevator with me. I would estimate the round silver piece of metal next to the bug is about 1.5″ diameter.
Signature: Matt

Tiger Moth: Histioea meldolae
Tiger Moth: Histioea meldolae

Dear Matt,
This gorgeous wasp mimic Tiger Moth is most likely
Histioea meldolae or another member of the genus based on a posting from our own archives submitted by Karl and confirmed by Arctiid expert Julian Donahue.  There is also a nice image on Hanna’s Bananas.

Thanks Daniel for the knowledge and the quick turnaround on my photo.  I appreciate it!

Letter 13 – Banana Moth from Canada is really from Costa Rica

 

Subject: What’s this Insect?
Location: Alberta Canada possibly Costa Rica
May 7, 2016 7:57 pm
We found this in a box of bananas that came from Costa Rica today and we cant figure out exactly what it is or if it came from there or here (Alberta Canada) Any help would be appreciated. The pic is the underside of it.
Signature: Kristy

Tiger Moth
Banana Moth

Dear Kristy,
This image has been open on our desktop for the past week as we have tried unsuccessfully to provide you with a species identification.  This looks to us like a Tiger Moth in the subtribe Ctenuchina to us.  We do not believe it is not a native species, but we wish you had been able to provide us with a dorsal view as most online images of moths are dorsal views.  We browsed through images from the subtribe Ctenuchina on BugGuide, but we could not find a conclusive match.  We will attempt to contact Lepidopterist Julian Donahue who is an expert in Tiger Moths to see if he can provide an ID.

Julian Donahue Responds
This is indeed a ctenuchid (or as currently classified, Erebidae: Arctiinae: tribe Arctiini, subtribe Ctenuchina): a fresh male Antichloris viridis Druce, newly emerged from its cocoon that accompanied bananas (its larval hostplant) imported from tropical America. In his 1975 paper Field reported examining specimens from numerous localities in the United States, three records from England, one from Germany, and two from British Columbia, Canada (Kaslo and Victoria). The native range of this species is from central or southern Mexico south through Central America to Venezuela, Colombia, and Ecuador.
This may be a new record for Alberta, however, so I am copying this to a couple of colleagues in that province.
Best wishes from the glorious Sonoran Desert, where the saguaros are now blooming on our property,
Julian

Thanks so much for the confirmation Julian.  We found an image of the ventral view on UK Moths and we found the common name Banana Moth used there as well as on Encyclopedia of Life.

Daniel;
I googled the information you gave me and that is exactly what it is!!  Thank you so much!
Kristy

Letter 14 – Tiger Moth from Brazil: Dysschema sacrifica

 

Subject: Black moth
Location: Porto Alegre, Brazil
February 17, 2017 9:11 am
Hi! Do you know what moth is this? It is a black moth with some white (maybe not pure white) details, not bigger than 3cm, with red and yellow tiny “hairy” details. It was seen in Porto Alegre, Brazil during the morning. Thanks in advance! Picture attached. – Brenda Lavoieri
Signature: Brenda Lavoieri

Tiger Moth: Dysschema sacrifica

Dear Brenda,
This is a Tiger Moth in the subfamily Arctiinae, and we scoured the pages of Insetologia until we located this image of
Dysschema sacrifica that appears to be the same as your moth.  The species is also pictured on BioLib.

Letter 15 – Tiger Moth: Ctenucha multifaria

 

Subject: Insect Unknown
Location: Central Coast CA
August 9, 2017 1:42 pm
Hello,
Could you please indentify this bug? Is it a wasp variety?
Signature: C Chandler

Ctenucha multifaria

Dear C Chandler,
This is not a wasp, but it is a Tiger Moth that mimics a wasp. 
Ctenucha multifaria has no common name, but we identified it on BugGuide.  According to BugGuide:  “Distal tip and entire costal edge of forewing narrowly white-marginned.”

Letter 16 – Tiger Moth from Italy is Discrete Chaperon

 

Subject:  Moth in Tuscany
Geographic location of the bug:  Near Siena, Tuscany, Italy
Date: 09/25/2017
Time: 11:42 AM EDT
Grateful if you could ID this moth found this morning. Thanks in advance.
How you want your letter signed:  Bob

Discrete Chaperon

Dear Bob,
This is a Tiger Moth in the subfamily Arctiinae.  We will attempt to provide you with a species identification.

Thanks, Daniel.  I did suspect a Tiger but can’t narrow it down any further.  I hope you are more able!
Best regards,
Bob.

Karl Provides an Identification
Hello Daniel and Bob:
It looks like a Discrete Chaperon (Erebidae: Arctiinae: Cymbalophora pudica). It is a variable species but on the whole it looks like a close match. Regards Karl

Thanks to you both.  Have copied you on a tweet.
Best,
Bob.

Letter 17 – Correction: The Magpie from the UK

 

Subject:  Moth?
Geographic location of the bug:  Nottingham
Date: 07/22/2018
Time: 04:54 PM EDT
Your letter to the bugman:  Please can you tell me what this is?
How you want your letter signed:  Elaine

The Magpie newly eclosed

Dear Elaine,
The nonspecific response is that this is a Tiger Moth in the subfamily Arctiinae, and it is freshly eclosed which means it has recently emerged from its pupal stage and its wings have not yet fully expanded and hardened, which is making our ability to identify it more difficult.  It most closely resembles a Garden Tiger Moth,
Arctia caja, as pictured on UK Moths where it states:  “Another species which was a favourite with early collectors, who selectively bred it to create unusual colours and forms.  Once a quite common moth in most of Britain, it seems to have declined in many places in the last few years.  It flies in July and August, and will regularly visit the light-trap.”  We would even entertain the possibility that a modern breeder might be releasing some “unusual colours and forms” back into the wild in an effort to help remedy that they “have declined in many places in the last few years” but the markings on the thoracic region as well as the scalloped wing edge eliminate the Garden Tiger Moth as the proper identification.  The only other Tiger Moth profiled on UK Moths that it resembles is the Cream-Spot Tiger Moth, Arctia villica, but in that species, the spots are white on a dark ground while your moth has dark spots on a white ground.  We are going to contact Arctiid expert Julian Donahue to get his opinion.

Dear Daniel
Thank you for looking into the moth that I saw it will be interesting to hear what your expert has to say. The moth wasn’t really moving and I got very close to it and moved it on it’s stick to photograph, I expected it to fly away but it stayed in the same place.
Thanks.
Elaine
Correction Courtesy of Julian Donahue:
Easy to be fooled by a colourful (since it’s British) un-expanded moth, isn’t it?

This is The Magpie, Abraxas grossulariata (Geometridae).
More images here:
All the best,

Julian

We had a bout of deja vú because according to UK Moths:  “A very distinctive species, this was a favourite with early collectors, who used to breed it to obtain unusual coloured and patterned forms.  Quite common in most of Britain, though less so in Scotland. … The moths fly in July and August and are regularly attracted to light.”

Authors

  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

    View all posts
  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

    View all posts
Tags: Tiger Moths

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