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Milkweed Tussock Moths

9-6-16  milkweed tussock moth larvae 20160830_1764Milkweed Tussock Moth caterpillars are responsible for eating all portions of milkweed leaves but the largest veins that contain sticky latex. They can tolerate the cardiac glycosides within the milkweed plant that are toxic to most other insects as well as certain mammals and birds. Like Monarchs, these caterpillars retain the toxic compounds as adults, and are therefore avoided by many predators.

Female Milkweed Tussock Moths lay their eggs in masses on the underside of milkweed and dogbane leaves, which their larvae will eat. The hatching caterpillars are gray and hairy, but in no time they have developed the tufts of hairs that give them their name. When fairly young, the larvae tend to stay together, skeletonizing the leaves they consume. As they mature, the caterpillars tend to wander, and it’s unusual to find large groups of them on a single leaf.

Many of the insects that feed on milkweed have orange and black patterns as both larvae and adults. These colors serve as a warning to would-be predators. One of the adult Milkweed Tussock Moth’s main predators is bats. While the moth possesses these colors during its larval stage, as a pale brown adult (the stage that nocturnal bats prey on them) it lacks the bright coloration (which would provide little protection in the dark) but has an organ that emits an ultrasonic signal easily detected by bats. The signal warns that an attack will be rewarded with a toxic and distasteful meal, thereby deterring predation.

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18 responses

  1. Kathie Fiveash

    How are the bats doing this summer? We never have them on the island, so I don’t have any idea.

    September 6, 2016 at 7:43 am

    • Afraid I don’t have any Summer, 2016 data yet on the bat situation. I’ve heard of more sightings than last year, but that is purely local, and not a scientific accounting!

      September 6, 2016 at 3:43 pm

  2. Bill On The Hill...

    My milkweed plants this season have been voraciously eaten upon here in the highlands of Corinth, Vermont and I suspect the above mentioned insect is the culprit although I have never spotted one as I have on numerous occasions been checking for Monarch eggs on the leaf undersides and as just like last season, no sign of eggs.
    However, just yesterday I saw my first monarch butterfly flying overhead on a beautiful sunny day down at the pond.
    My first sighting in close to two years now…

    September 6, 2016 at 8:01 am

  3. Peter Hollinger

    I never knew about the ultrasonic deterrent. Evolution is amazing.

    September 6, 2016 at 8:24 am

  4. Rita Pichette

    There is a silk yarn called Tussock silk. Is that from a type of these caterpillars, do you know?

    September 6, 2016 at 8:34 am

  5. Marilyn

    I’m confused: Do the bats eat the moths knowing that the moths are toxic and bad-tasting?

    September 6, 2016 at 8:41 am

    • Good question! I assume that the signal works often enough to preserve the species, but not often enough to fool every bat?

      September 6, 2016 at 9:09 am

      • I shouldn’t have used the word “fool” – warn is much better!

        September 6, 2016 at 9:09 am

  6. Fascinating…the monarchs and swallowtails are enjoying nectaring on our zinnias. Will miss them when time to go.

    September 6, 2016 at 9:18 am

  7. Viola

    So that’s what those critters are! Very colorful and I’ve always wondered. Thanks, Mary

    September 6, 2016 at 9:28 am

  8. MMCBushnell .

    Thank you Mary for all your fantastic knowledge and lovely photos.

    Last night as the sun was lowering in the sky we watched a dance of dragonflies, about 50, their wings catching the light as they soared over our meadow of wildflowers and grasses. They seemed to be enjoying the evening air and not really chasing one another. In fact, they darted away from one another when they came close.

    We have not idea what we were seeing and enjoying. Were they a hatch? What will happen to them next. Why was this behavior imbedded in their genetic code. If you have a past post that would help us understand, we would like to learn more. Marcia and Ken Bushnell

    On Tue, Sep 6, 2016 at 7:22 AM, Naturally Curious with Mary Holland wrote:

    > Mary Holland posted: “Milkweed Tussock Moth caterpillars are responsible > for eating all portions of milkweed leaves but the largest veins that > contain sticky latex. They can tolerate the cardiac glycosides within the > milkweed plant that are toxic to most other insects as well ” >

    September 6, 2016 at 9:35 am

    • Hi Marcia and Ken,
      The dragonfly swarm you describe is an amazing sight. There are two types of dragonfly swarms: feeding swarms (dragonflies congregate in a small area, often where there has been a hatch of insects recently upon which the dragonflies feed) and migratory swarms (massive numbers of dragonflies migrate to overwintering sites). My guess is that if they weren’t all headed in the same direction, they were feeding, not migrating, but migrating dragonflies have to feed, too, so I can’t be sure! I haven’t managed to get a photograph of this phenomenon, thus, I have no blog post on it, but hope to some day!

      September 6, 2016 at 3:37 pm

  9. Linda

    Do the bats suffer ill effects from eating the moths? As Curley says:” Fascinatin’!”

    September 6, 2016 at 9:45 am

    • Another question I do not know the answer to! Will see if I can find one.

      September 6, 2016 at 2:48 pm

  10. Tami

    Had my first sighting of these guys last year when they consumed the milkweed plants my landlady was so proud of. Being naturally curious myself, I had to look them up and find out all I could about them. Three of them reduced the leaves on two large milkweed plants to complete skeletons in less than 24 hours. I was fascinated, landlady was mildly horrified, she was “saving” them for monarchs.

    September 6, 2016 at 3:56 pm

  11. Mary,
    I have been watching three of these little guys munching away near the path through my meadow. They look like someone knitted them out of orange and black yarn.
    I have your Naturally Curious book and the Milkweed book, (which has fallen apart from overuse, so I put the pages in sheet protectors and a three-ring binder.)
    I have a field full of milkweed which used to attract many Monarchs, among all the other bugs you feature in your book, but this year not a single confirmed Monarch sighting, some Frittilaries, a few Viceroys, but NO Monarchs. I am bereft!
    Thank you for all your contributions to our collective natural knowledge. I hope to see you in person some day, since I am just across the river in NH.

    September 7, 2016 at 3:46 pm

    • Thank you so much, Gale. I’m doing a book signing at the Norwich Bookstore in October and at the Montshire Museum in November, should you be free and want to come by!

      September 7, 2016 at 7:27 pm

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