Black Arches Caterpillar: Essential Facts for Enthusiasts

The Black Arches Caterpillar is the larval stage of a fascinating species of nocturnal moths, Lymantria monacha.

These caterpillars love to feed on oak leaves and you can spot them usually during April to June, after they come out from overwintering as eggs.

Though the Black Arches Caterpillar may not be among the most common, its striking appearance and remarkable life cycle are certainly notable.

Let’s learn everything there is to know about the captivating Black Arches Caterpillar.

Black Arches Caterpillar
Source: Ilia UstyantsevCC BY-SA 2.0, via Wikimedia Commons

Black Arches Caterpillar Basics

Physical Features

The Black Arches moth, also known as Lymantria monacha, is a moth species from the Lymantriidae moth family in the Erebidae family.

The adult moth has white forewings with black wavy arches. Its hindwings are light brown with white fringes.

Adult moth wingspan is 44-47 mm (for males) and 48-54 mm (for females).

The caterpillars are found either in shades of green or brown, featuring prominent yellow stripes on their body.

The subdorsal stripe is bordered with white and black, while the spiracular stripe has minimal black edging underneath.

The spiracles are white with a black outline. The caterpillar’s head is either green or brown, adorned with a brief yellow line passing through the top eyes.

While the caterpillars are usually seen in Apr-May, the adults can be seen in Jun-Aug.

Black Arches Caterpillar
Black Arches Caterpillar

Origins

The native habitat of the Black Arches species ranges across Europe and is commonly found in the United Kingdom.

These moths primarily inhabit woodland areas, particularly where their preferred host plants, such as conifer trees and oak trees, are abundant.

Life Cycle and Behavior

Larvae

  • Green: Young larvae are green with a white stripe.
  • Brown: As they mature, they turn brown with white spots.

Black arches caterpillar larvae typically hatch in the spring and feed on various trees like oak, birch, and willow.

Larvae showcase individualistic behavior, as they reside on and consume the host plant’s leaves.

Pupa

  • Time: Pupa stage lasts for about 20 days.
  • Color: They are dark brown and well-camouflaged.

When fully grown, the larvae will pupate and form protective cocoons.

Within these cocoons, the caterpillar undergoes its transformation, becoming a pupa.

Adults

Adult males and females display slightly different appearances and behaviors.

  • Size: The females are 1/2 to 3/4 of an inch long with a 1 3/4 to 2 1/4 inch wingspan. The males are about 1/2 of an inch long with a 1 1/3 to 1 3/4 inch wingspan.
  • Wings: The females have elongated wings.
  • Antennae: The females have thread-like antennae. The males have comb-shaped antennae.

Males are more active at night search for females to mate with, while females release pheromones to attract males.

Habitat and Distribution

Europe

In Europe, the Black Arches Caterpillar is widespread, with its habitat spanning various woodlands and forests. They particularly favor regions with an abundance of:

  • Pine
  • Willow
  • Birch

India

In India, the Black Arches Caterpillar’s habitat predominantly consists of pine woodlands.

While not as common as in other regions, they can also occasionally be found in areas with ash, willow, alder, and birch trees.

 United States & CanadaEuropeIndia
Pine
Ash 
Willow
Alder 
Birch

Diet and Host Plants

Oak Trees

Black Arches Caterpillar primarily feeds on oak trees, which are an essential part of their diet.

Quercus, commonly known as oak, and specifically Quercus robur, or Pedunculate Oak, are their preferred species. They are usually found on these trees during springtime.

Other Common Plants

Besides oak trees, they may also feed on other common plants such as aster and goldenrod. These plants serve as alternative host plants for the caterpillar, allowing for diversity in their diet.

ComparisonOak TreesOther Common Plants
Preferred Host PlantQuercus roburAster and Goldenrod
SeasonSpringSpring
Purpose in DietPrimary dietlternative hosts

Do Black Arches Caterpillar Bite or Sting?

No these caterpillars do not have the capacity to bite or sting.

They do not possess the urticating hairs that can cause itching on rashes on humans either.

These caterpillars and moths are harmless and beautiful creatures.

Conclusion

In our exploration of the Black Arches Caterpillar, we’ve delved into its unique characteristics, life cycle, and habitat preferences.

This captivating caterpillar, a larval stage of the Black Arches Moth, showcases a striking appearance and plays a significant role in its ecosystem.

Found predominantly in woodlands and gardens, its diet primarily consists of oak leaves, though it occasionally feeds on other plants.

As enthusiasts, it’s essential to appreciate and protect these creatures, ensuring their continued presence in our natural world.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about Black Arches Caterpillars. Scroll down to have a look at some of them.

Letter 1 – Black Arches Caterpillar

unusual caterpillar
Hi from Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada. I’m way out of my league on caterpillars and the local experts are stumped as well. Sure hope you can point me in the right direction. I just don’t want to disappoint members of the public who are interested in nature. Kind regards,
Berry Wijdeven
Species at Risk Recovery Coordinator
Ministry of Environment

unusual caterpillar
Hi Berry,
Here is the photo of the strange caterpillar which I found on a lavatera plant at our place. We have never seen one like it before, and it would be interesting to find out what kind of moth or butterfly it turns into. I just left it alone, and it disappeared—maybe we will spot an unusual butterfly in the spring. Regards,
Marlene Specht

Hi Barry and Marlene,
Our only thought was this might be one of the Hooded Owlet Moth Caterpillars in the genus Cucullia, so we checked BugGuide. We followed a link to the genus Melanchra and found your caterpillar, known as the Black Arches, Melanchra assimilis.

It is an Owlet Moth that feeds on a wide variety of plants, but it does not list Lavatera. The caterpillar is found in both green and brown forms, both with the bold yellow stripes and black outlines depicted in the photo you provided.

Letter 2 – Black Arches Caterpillar

Black Arch Caterpillar
Dear bugman,
I found this Black Arch caterpillar while frolicking in Shenandoah National Park. I’ve read somewhere that they are rare to unusual, but they are everywhere out here! I’ve greatly appreciated your help in the past and thought you’d like to add this picture to your collection.
Holly
Shenandoah National Park, VA

Black Arches Caterpillar
Black Arches Caterpillar

Hello Holly,
We are happy our site proved helpful with your identification. It seems like the Black Arches Caterpillar, Melanchra assimilis, is correct.  We did some internet research and found some information.

The Butterflies and Moths of North America website indicates a very small reported range in Montana.  BugGuide shows more extensive data, reporting the species from Montana, Minnesota, Maine and New Hampshire, but on the information page for the species, BugGuide indicates that it ranges to Virginia.  

It is also indicated that the species is “uncommon to rare, according to Charles Covell ” and later  in uncredited information that ‘larvae feed on bracken, sweetfern, goldenrod, st. johnswort, alder, ash, birch, willow.

Wagner lists also aster, goldenrod, mullein, raspberry, and tamarack and concludes “primarily a generalist on low-growing plants.’ ”  We find it odd that the caterpillar would be rare with such an extensive list of food plants.

If you say they were very numerous, perhaps the real explanation is that the populations are highly localized and may be quite plentiful where they are found.  We found the previous posting on our site that you credited with providing your identification.  

We are very excited to see if a new feature that our web host has provided for our site works properly.  Now, the five closest matching posts will appear as links with your post, which should lead our readership to other posts of the same species.

Authors

    by
  • 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.

  • 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.

1 thought on “Black Arches Caterpillar: Essential Facts for Enthusiasts”

  1. Can’t quite see the top of the head, but this looks more like the Striped Garden Caterpillar, Trichordestra legitima to us, Wagner page 415

    Reply

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