24 May 2009

Can anyone I.D. this grey caterpillar?


I found this little fellow twitching on top of leaf litter in a deciduous woods near Madison, Wisconsin. I didn't recognize his species, and when I picked him up, everything became even more bizarre...

The caterpillar is about 6cm in length, dark grey in color, with a series of tubercles along the dorsal aspect of the body segments. There is a horn-like dorsal appendage near the rear, and another bifurcated horn behind that. The margin between dorsum and abdomen appears to be gently "fringed."

On the ventral surface near mid-body are four large holes, with perhaps another smaller one near his forelegs. Nothing is oozing from these holes.

Left undisturbed, he/she remains virtually motionless. Overnight in a jar in my office there was no change of position. But when disturbed the cat twitches forcefully with a side-to-side motion.

I can only assume that the caterpillar was parasitized by a ?wasp, and that the parasitic young have already emerged from those holes. I'm keeping him for now in case another creature emerges from one of the other body segments.

I spent an hour last night searching for an identification of this caterpillar. I viewed most of the images at the excellent USGS Caterpillars of Eastern Forests website, then paged through several years of posts at the (outstanding) What's That Bug site, and also found nothing at Duke University's beautiful photoblog of moth caterpillars.

If any TYWKIWDBI visitors have suggestions or know of friends with entomologic skills to whom you could forward this link, I would be greatly appreciative.

First update: Courtesy of Dr. Pellitteri at the University of Wisconsin, I believe this caterpillar is in the Catocala [Underwing] genus. I'm looking for more details...

Second update: I finally was able to restrain the caterpillar sufficiently to examine the abdomen more closely (the Catocala caterpillars are apparently famous for their thrashing maneuvers). Dr. Pellitteri had suggested that the dark patches were areas of coloration, and I now think that is correct. This will come as a great relief to those of you who have been losing sleep worrying about critters erupting from the poor cat's abdomen. I'm not sure WHY coloration would be placed in such a normally unseen location, unless it serves to deter predators (birds etc) who turn the caterpillar over. This genus of caterpillar pupates underground or under leaf litter on the forest floor, so I've moved him to a jar with several inches of peat into which he can tunnel if he's ready to pupate, and I've given him some oak leaves to munch on in the meantime. If anything interesting happens, I'll post another update.

21 comments:

  1. I would suggest contacting UW Extention entomologist, Dr. Phil Pelliteri. He's the local bug guy who knows everything!

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  2. Hi Stan, Its Dave D.
    Ask Phil!
    http://www.uwex.edu/ces/ag/directories/documents/pellitteri%20phil.pdf

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  3. you've got to update us on this...I'm getting creepy crawly feelings all over after looking at/reading about this caterpillar.

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  4. Query sent to Dr. Pelliteri. Stay tuned...

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  5. Wouldn't thrashing movements make it vulnerable to birds and other predators by alerting them to it's presence?
    Perhaps it does have a microscopic parasite which needs to complete it's life cycle in a bird.
    What else would thrashing about achieve?
    I'm sure I've heard of some parasite which tries to get it's host eaten.

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  6. The thrashing about only occurs AFTER the caterpillar is disturbed; left alone it lies virtually still and would be unnoticed, especially against the bark of a tree.

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  7. I have been researching these little critters for about a week now and I am so happy I found this site! I live near Oregon, WI and last week when building a fence I found one and it was the meanest thing ever. (That is part of what made me want to look more into it, and having not seen it before.) I grabbed a clean cup and another cup, because to be honest it was wriggling all over if I even came near and it appeared to jump at you when you came near it. I got it in the cup and released it in the front area of my house (away from where it could be augered that day with power equipment.) The other day I was out there again and I saw another one (maybe the same one, who knows... could have crawled back to his area which is about 100 yards from where I moved it initially.) I was really interested in finding out about this caterpillar because of his thrashing dance skills and just overall crankiness lol. I am soooo happy that you posted this in the first place, you ended up helping others who are just curious about what it could have been. I have been interested in bugs since I was a girl and to this day I get really excited it I see something new! I was fascinated by his demeanor and markings and I did notice that a part of his little cranky dance was rolling over and flashing me his red splotches on his belly. These little creatures are amazing, I hope I see more of them. Now I know what to look for and tonight I will be leaving a light on to see if maybe I can get a glimpse of a beautiful moth and correlate the two. Thanks again!

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  8. I just found one of these on my living room floor, probably brought on the dog. What is it? We live near woods in Roscoe, IL about 1 1/2 hrs. south of Madison. I wouldn't want to release it if it is injurious to our trees.

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  9. It's one of the many hundreds of types of Catacala caterpillars. It will eventually become one of the more familiar "underwing" moths.

    http://en.wikipedia.org/wiki/Catocala

    Here's another link with some photos -

    http://www.silkmoths.bizland.com/catilia.htm

    It might eat a few leaves from an oak tree; I wouldn't worry about it.

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  10. We live in Cedar Park Texas and just 5 minutes ago we found one in our front yard.Creepy Looking/daughter scared.Would like too know ourselves

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  11. We live in South Louisiana and have these things. They really ARE aggressive. Freaky. They act like they would bite. Are they poisonous?

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  12. Hi! Thanks to you, I was able to i.d. this caterpillar when I found one the mulch this evening. :) So, thank you for the post!

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  13. My son found one under a rock, it was the wierdest thing I have ever seen, We live in New JerseyI took a video of it's crazy twitching dance but cant figure out how to upload it from my phone. Thanks for posting! I am much less disturbed by the wierd little guy now that I know what it is! We are setting it lose since our past attempts at keeping caterpillars never worked out well...for the caterpillar that is.

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  14. Hello, I would like to thank you for the blog post here. I found one of these today while trimming bushes, and it shocked me quite a bit when the little bugger latched onto my finger and started trying to bite me (!). It's aggressive "grumpy" behavior is what made me so interested in it, so I decided to jump on google and I was able to find this after querying a few pages under "Grey caterpillar" (I know, pretty lucky right?)

    These little buggers are quite amusing. They stay still for a majority of the time. I actually went to check on him and he is still sitting on the exact same branch in the same spot as he was earlier today... 7 solid hours of no movement! It makes me wonder, when do these guys ever eat? Probably at night or something.

    Very interesting creatures, and again thank you for the post!

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  15. I also would like to know what kind of catterpillar this is. I had one fall on me once. It did bite didn't hurt or cause any sickness. Just startled me more then anything. Then proceeded to show it to people trying to figure out what it was.

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  16. yes I found one also in south louisiana it has moved a total of 3 inches up a bucket since yesterday we did not touch it good thing with it being called parasitic and all I am still concidering to pour drain cleaner on it and smash it with a stick then throw it far away

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    Replies
    1. It's just a larva of an underwing moth. After it comes out of the cocoon it will look like this -

      http://www.silkmoths.bizland.com/catilia.htm

      It's no danger to you. You don't need to hurt it.

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    2. It's NOT parasitic. What they were saying is that they thought it had been parasitized ON by a wasp, but that wasn't true either. It won't do any damage at all, other than acting cranky :)

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  17. http://en.wikipedia.org/wiki/Catocala_ilia

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  18. I live in Cuero, Tx and found one in my front yard. The only different was it was about half a foot long and the underside was white-ish with the black spots. I ended up getting rid of it because I didn't want one of our dogs to eat it, but was curious as to what it was. It came from one of the pecan trees in our front yard.

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