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Monkey Slug Season

Congratulations to Rinky Black, who was the first person to accurately identify the Mystery Photo as a Monkey Slug!

Some of our dullest-looking moths started their lives out as colorful, bizarrely-shaped caterpillars.  In particular, there is a family of caterpillars (Limacodidae) known as “slug caterpillars” which come in all kinds of unusual forms and colors.  They can be naked or densely hairy, and they usually have stinging hairs. The Hag Moth (Phobetron pithecium), found throughout eastern North America, is one such moth. Whereas the adult moth is a dull brown, the caterpillar stage is anything but dull.  Known as the Monkey Slug, the caterpillar stage of this moth has three pairs of long “arms” and three additional pairs about half as long.  Its appearance has been likened to a tarantula (many of our insectivorous birds winter in the tropics, where there are tarantulas (which the birds avoid), and therein lies the reason for the caterpillar to look like one).  Although most photographs make Monkey Slugs look large, they measure only about an inch in diameter. Adult moths bear a slight resemblance to bees and wasps.

What is eye-catching about Monkey Slugs (as well as other slug caterpillars), besides their bizarre appearance, is the way in which they move.  Monkey Slugs glide – instead of the typical prolegs (located behind six true legs) they have suckers (see bottom right inset).  This gliding is responsible for its being classified as a “slug” caterpillar, for it moves much like a slug does.  The Monkey Slug is one of the slug caterpillars that does not sting, so you can handle it safely should you find one. (Thanks to Kathy and Geoff Marchant for photo op.)

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12 responses

  1. Alice

    What a bizarre caterpillar, looks more like an under-water ‘something.’

    September 4, 2019 at 7:19 am

  2. Martha Adams


    Sent from my iPad


    September 4, 2019 at 7:37 am

  3. Bill On The Hill

    This has got to be the most unusual ” thing ” I have ever seen with respect to caterpillars.
    It looks very alien like!
    Is that a pair of eyes I see?
    Bill… :~)

    September 4, 2019 at 8:58 am

    • What you’re seeing (that’s usually hidden under a flap) are its mouthparts, Bill. Good eye!

      September 4, 2019 at 11:43 am

  4. Maine naturalist

    I sincerely had no idea these things exist in our region. You’re providing a real service here in terms of great photography and solid natural history information. Thanks!

    September 4, 2019 at 9:07 am

    • You’re more than welcome. We’re all learning every day, including me!

      September 4, 2019 at 11:44 am

  5. Libby Hillhouse

    Do these slugs have a favorite food source? Where are they most likely found??? And if it’s a caterpillar, why is it called a slug?

    September 4, 2019 at 9:21 am

    • Hi Libby, It’s called a slug because of the way it moves (like a slug — glides from one spot to another). They are not fussy eaters — beech, maples, oaks,apple, cherry, dogwood, hickory, walnut and willow to name a few of the leaves it eats!

      September 4, 2019 at 11:46 am

      • Libby Hillhouse

        Thanks! I’ll sharpen my hunting and observation skills!

        September 4, 2019 at 1:14 pm

  6. hellomolly

    Wow, that is definitely one of the most unusual creatures I’ve ever heard of! Thanks for sharing.

    September 4, 2019 at 10:08 am

  7. cannjen

    Did you know of the monkey slug? Pretty cool little fella 🙂

    Sent from my iPad


    September 4, 2019 at 6:25 pm

  8. kathryn

    A monkey slug. Never heard of him. I just googled images of the little guys and they are really something. Thanks, Mary!

    September 4, 2019 at 7:16 pm

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