Over 50 Caterpillars Found in Colorado (6 Are Poisonous)

Written by Keyana Beamon
Updated: August 15, 2023
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Colorado is a beautiful state and home to many types of insects. Depending on what parts of Colorado you are in, you may encounter some unique species of caterpillars! Caterpillars are a type of insect that transform into a butterfly or moth. Like many insects, some can be poisonous or can cause irritation to the skin if touched. This insect comes in various colors and is known for eating as much as they can before they are ready to transform. The following article will list over 50 types of caterpillars seen in Colorado and which ones you should stay away from!

Poisonous Caterpillars

1. Lo

The Lo caterpillar are highly venomous and have a painful sting. If you come in contact with this creature, use scotch tape to remove its tiny spines from your skin and ice the affected area. Take antihistamines and pain relievers to help with symptoms. The Lo caterpillar is light green, with red and white stripes down its sides. The remarkable insect turns into the Lo moth.

Hairy Caterpillar

The Lo caterpillar live around hackberry and willow trees.

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©Rodrigo Bellizzi/Shutterstock.com

2. Puss

The Puss caterpillar are venomous insects that can grow up to 1 inch long. They are covered with soft, brown, fur like hair, giving them a wool like appearance. The Puss caterpillars spines are filled with toxins that can cause severe irritation to the skin. The population of this species is determined by food availability and weather. Once the Puss caterpillar builds its cocoon, it will break free 2 weeks later turning into the Flannel moth.

A puss caterpillar in Arenal Volano National Park in Costa Rica

Observe this interesting and furry creature from afar, but don’t touch it!

©Adriana Margarita Larios Arellano/Shutterstock.com

3. Spiny Elm

The Spiny Elm caterpillar are seen on elm trees and have bright red or orange dots on its back covered with black spikes. The white bristles around its spines contain poison. If your dog seems interested in this insect, make sure they do not consume these creatures. The Spiny Elm caterpillar turns into the Cloak butterfly.

Spiny caterpillars are dangerous and poisonous. If touched human skin, will feel itchy and hot.

The Spiny Elm Caterpillar can grow up to 2 inches long.

©Gunawan Alam/Shutterstock.com

4. Hickory Tussock Moth

The Hickory Tussock Moth caterpillar has fuzzy white hair with black spots. This caterpillar should only be observed and not touched because their hair contains a toxin that can cause severe allergic reactions. Their hair will get stuck in your skin, causing redness and a slight burning sensation. Their cocoons can also cause skin irritation.

Hickory Tussock Moth Caterpillar - Lophocampa caryae

The Hickory Tussock Moth Caterpillar can grow up to 1.7 inches long.

©Jay Ondreicka/Shutterstock.com

5. Western Tent Moth

The Western Tent Moth Caterpillar is black with red and yellow spots and stripes. This insect got its name because of the tent-like pattern on its back. You can see them in wooded areas feeding on grass, leaves, and other vegetation. Although this caterpillar is not poisonous, it can produce a substance that causes the skin to become irritated.

A close-up shot of a bunch of Western tent caterpillar's during the day

The scientific name for the Western Tent Moth is

“Malacosoma californicum.

©Wirestock Creators/Shutterstock.com

6. Slug

The Slug is one of the most common type of caterpillars found in ash and deciduous trees throughout Colorado. If these tiny creatures are touched or frightened, it will raise its head and spread its tail. They will then spray a yellow foul liquid that causes irritation of the skin, but is not poisonous.

The spiny Oak Slug - Euclea Delphinii - is the larval form Caterpillar wandering through the woods in Kerala, India

The Slug caterpillars scientific name is “

Acharia horrida


©AKP Photos/Shutterstock.com

Non-poisonous Caterpillars

7. Monarch

The Monarch caterpillar is a plump insect with black, white, and yellow stripes. This caterpillar is toxic because of the number of milkweed plants they eat. If you are looking for this beautiful creature, they hang out wherever milkweed is found.

Seven days old Monarch caterpillar resting on a milkweed leaf, a side view

The Monarch can be found in mountains and plains of Colorado.

©Sari ONeal/Shutterstock.com

8. Parsley

9. Curve-line Owlet

10. Anise Swallowtail Butterfly Cat

11. Question Mark

12. Cabbageworm

The cabbageworm caterpillar is light green and has small yellow dots on its side. The caterpillar hosts plants are cabbage, kale, broccoli, and chard. The cabbageworm is not native to North America. They were shipped here from Europe in a crate full of cabbage! This insect can be a nuisance because of its ability to destroy a large number of crops.

Cabbage worm caterpillar pest eating a spinach leaf

The scientific name for the cabbageworm caterpillar is “

Pieris rapae


©Kelsey Armstrong Creative/Shutterstock.com

13. Yellow-haired Dagger Moth

14. Yellow-necked

15. Salt Marsh Moth

16. Zebra

17. Alfalfa

18. Cabbage Looper

19. Cloudless Sulphur

20. Woolly Bear

The Woolly Bear caterpillar has dense, coarse hair that will irritate the skin if touched. They are black with a rusty-red color band in the middle of its back. This caterpillar is found in groups at the bases of grass, weeds, and other plant material.

Wolly bear caterpillar on stick.

The Woolly Bear caterpillar has a special substance in their blood that will cause them to freeze in cold weather and thaw out in Spring.

©Loc’d Lense/Shutterstock.com

21. Camouflaged Emerald Moth

22. Common Buckeye

23. Eastern Tent

24. Large Maple Spanworm

25. Viceroy

The Viceroy caterpillar lives in the open forests and fields of Colorado. This interesting looking creature is either brown or green with white markings that resemble bird droppings! It is not poisonous; however, they cause predators to have an upset stomach because of the amount of salicylic acid they consume.

Viceroy Caterpillar, Limenitis archippus

The Viceroy are highly active in the spring and summer time.

©Malachi Jacobs/Shutterstock.com

26. Hooded Owlet Moth

27. Milkweed Tussock

28. Hitched Arches Moth

29. Forest Tent

30. Polyphemus Moth

31. Red-Humped

32. Variegated Fritillary

The Variegated Fritillary caterpillar are red with black and white stripes. This particular caterpillar can be seen around meadows, open lots and fields because they love to consume violets, pansies, and passion flower.

A colorful Variegated Fritillary caterpillar (Euptoieta claudia) feeds on some clover in preparation for its cocoon transformation.

The Variegated Fritillary caterpillar are active between late spring and early fall.

©Brett Hondow/Shutterstock.com

33. Afflicted Dagger

34. Genista Broom

35. Galium Sphinx

36. Eastern Tiger Swallowtail

The Eastern Tiger Swallowtail caterpillar are bright green with black and white like eyes. This caterpillar can be seen in northeastern colorado, eating various plants, tulip trees, and wildflowers. The young Eastern Tiger Swallowtail caterpillar will mimic the appearance of bird droppings to ward off predators.

Eastern Tiger Swallowtail Caterpillar (Papilio glaucus)

The Eastern Tiger Swallowtail can grow up to 2 inches.

©Jay Ondreicka/Shutterstock.com

37. Cecropia Motri

38. Pipevine Swallowtail

39. Owlet Moth

40. Silver-Spotted Skipper

The Silver-spotted Skipper caterpillar can grow up to 2.5 centimeters long and are some of the smaller types of caterpillars in Colorado. The caterpillar is yellowish-green with a wrinkle like appearance on its body. They also have a large brown head with a pair of orange false eyes.

Silver-spotted Skipper Caterpillar (Epargyreus clarus)

The Silver Spotted Skipper rarely visit yellow flowers!

©Jay Ondreicka/Shutterstock.com

41. False Unicorn

42. Luna Moth

43. Blinded Sphinx Moth

44. Silvery Checkerspot

45. Orangedog

46. Imperial Moth

47. Purslane

48. Bent-Line Gray Moth

49. Spotted Tussock Moth

The Spotted Tussock Moth caterpillar can grow up to 2.5 inches long and are seen between late summer and late fall in the foothills of Colorado. This caterpillar like to feed on trees and shrubs, which can be a nuisance to gardeners. The Spotted Tussock Moth have yellowish-white hairs with black, yellow, and orange stripes down its back.

A yellow and black spotted tussock caterpillar crawls on leaves

The Spotted Tussock Moth larvae turns into the

Tiger moth


©Amelia Martin/Shutterstock.com

50. Thistle

The Thistle caterpillar can grow up to 1.5 inches and have sharp spikes on its back. As it continues to grow older, they become more yellow in color with four black stripes and several yellow spots on its back.

51. American Dagger Moth

52. American Lady

53. American Lappet Moth

54. Unicorn (True Unicorn)

The Unicorn caterpillar obtained its name because of its colorful- unicorn like appearance. It has bright yellow and blue stripes along with bright orange tufts. This insect lives on Willow, Alder, and Oak trees throughout Colorado. The Unicorn caterpillar can grow up to 2 inches long.

Unicorn Caterpillar moth feeding on a cherry tree leaf

The Unicorn caterpillar got its name because of the horn-like protrusion coming from its head.

©Sari ONeal/Shutterstock.com

55. Two-Tailed Swallowtail Caterpillar

56. Hahncappsia Moth

57. Red Admiral Butterfly


Most caterpillars can be found all over Colorado; however, they love to be in mixed deciduous forests to eat as much as they can. The forests of Colorado provide enough food and shelter until they are ready to transform into a beautiful butterfly or moth. Depending on which species of caterpillar you are seeing can depend upon what type of vegetation is available. For example, if you have milkweed in your garden or live in an area abundant with milkweed, then the Monarch caterpillar will be seen more in your area.

The photo featured at the top of this post is © Jay Ondreicka/Shutterstock.com

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About the Author

Keyana is a licensed veterinary technician who has been working with animals for more than 10 years. She has done a mixture of emergency, preventative, and shelter. She loves to mentor others and has recently started a podcast about the ins and outs of veterinary medicine. In her free time, she love to watch/read anything crime related, tend to her garden, try new foods, work on puzzles, and hangout with friends.

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