Wednesday, June 27, 2012

Wasp Wednesday: Elm Sawfly

Finally! I have been looking for an adult Elm Sawfly, Cimbex americana, for decades, ever since seeing pinned specimens in college back in the early 1980s. My quest ended this past Monday, June 25, when I happened upon a huge male specimen in the middle of a meadow in Emerald Valley, Colorado.

The Elm Sawfly is a large, robust insect about 20-25 millimeters in body length. They appear even bigger, especially the males with their beefy “thighs” (femora) on the middle and hind legs. The jaws of both genders are strong, and used to strip bark from twigs, sometimes girdling them in their efforts to reach the tasty sap. The clubbed, relatively short antennae are a characteristic of all members of the family Cimbicidae. The overall plump appearance often convinces people that these insects are bees rather than wasps.

The larvae of these wasps feed not on pollen, nectar, or other insects paralyzed and provided by their mothers. Instead, sawfly larvae feed on plant foliage. Despite the name “Elm Sawfly,” Cimbex americana feeds on other trees as well, especially willow, but occasionally on basswood (linden), birch, poplar, alder, and maple. At maturity, the caterpillar-like larva can be two inches (43 millimeters or so) long.

How do you tell a sawfly larva from the caterpillar of a butterfly or moth? True caterpillars have no more than five (5) pairs of prolegs, the “false legs” along the length of the abdomen that look like suction cups. Sawfly larvae have seven (7) pairs of prolegs.

When they are disturbed, Elm Sawfly larvae coil themselves and prepare to release volatile chemicals from glands in the thorax if necessary for their self-defense. They also rest in a coiled position. The rough, pebbly texture, and black midline dorsal stripe help to identify these greenish, yellowish, or whitish larvae. Look for them mostly between June and October, but note that I found the specimen pictured here on May 7 in South Carolina.

The mature larvae crawl to the ground and spin a tough, papery cocoon around themselves amid leaf litter or just below the surface of the soil. There they remain as larvae through the winter, pupating the following spring. There is only one generation per year.

The adults are sexually dimorphic in color. Shown here is a male. Females have the abdomen black with yellow horizontal bands interrupted in the middle. There is some variation in color and pattern from one geographic area to another. This is a very widespread insect, found in the U.S. and Canada from the Atlantic seaboard to the Rocky Mountains, and also the Pacific coast states north to Alaska.

Females of the Elm Sawfly use a saw-like ovipositor to insert eggs in the leaves of the host tree. They do not have a stinger. Both genders simply look intimidating. Males may defend territories. The one I found on Monday I startled from its perch, but after a wide orbit it flew right back to that one shrub, elevated only a little above surrounding vegetation.

The Elm Sawfly does have its enemies, including an egg parasite, Trichogramma minutum, a very tiny type of wasp. A large ichneumon wasp, Opheltes glaucopterus barberi, is an internal parasite of the sawfly larva. The sarcophagid fly Boettcheria cimbicis has been reared from the pupal cocoons of the Elm Sawfly.

See if you can find this species in your own region. Do you find it to be common? Do populations vary from year to year? While this species is rarely a pest (it has been known to defoliate shade elm trees, especially in the northern Midwest), it would pay to know more about it.

Sources: Drooz, Arnold (editor). 1985. Insects of Eastern Forests. Washington, DC: U.S. Department of Agriculture, Miscellaneous Publication No. 1426. 608 pp.
Essig, E. O. 1958. Insects and Mites of Western North America. New York: The Macmillan Company. 1050 pp.
Furniss, R. L. and V. M. Carolin. 1977. Western Forest Insects. Washington, DC: U.S. Department of Agriculture, Miscellaneous Publication No. 1339. 654 pp.
Stein, John D. 1974. Elm Sawfly. Forest Pest Leaflet 142. Washinton, DC: U.S. Forest Service, U.S. Department of Agriculture.

97 comments:

  1. Noticed some Elm Sawfly larvae feeding on Willow leaves this summer. Located in the state of Maryland. Will keep my eyes open for adults and will check for larvae again next summer. The size of the larvae got my attention.

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  2. Thanks for sharing your observations, Mike!

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  3. I saw an elm sawfly larva here in Vermont about 1 month ago; it was crossing a dirt road. My friend and I had a heck of a time id'ing it, as we were looking in a moth/butterfly guide. You can see a photo here: http://northernwoodlands.org/witwit/mellow-yellow-fellow. Thanks for the great info on this critter.

    Meghan

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  4. just found a bunch of these in Reliance, South Dakota. Eating up the America Elm.

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  5. Just found one in Albertville, MN. It was on the ground under a Basswood tree.

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  6. I saw 3 or 4 in a tree in my yard, but judging from the little poop balls all over my patio, there are a bunch of them.

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  7. I have them all over a couple Pecan trees. They first popped up around mid-April here in Central Texas. They don't seem to be doing much damage, but they typically feed and then crawl down the trunk to the soil and then disappear.

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  8. I just found one of these today in my yard , ( Box Elder SD) it took most of my day trying to figure out what this was.. I have never seen one before..

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    1. Congratulations! The only adult one of these I've ever seen is the one pictured above.

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  9. I found one here in Newfoundland, Canada this weekend!!! I have NEVER seen anything like it here before and hope not to see another!

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    1. Ha! They can certainly be intimidating, but maybe I can take your share of future appearances of these wasps.

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    2. I just found one today on my porch in central and. Never seen one before

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  10. I think I may have seen one in my yard. I was scared because I thought it was a huge wasp! I wish I could post pictures because I took a bunch and also a video.

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  11. I found one in its larvae state on my deck today...I would like to know if they are harmful because my kids would like to keep it and watch it change..Thank you

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    1. They are not dangerous in the least. The larva should spin a cocoon shortly if it is large in size and off of its host plant. Simply put the insect into a ventilated container and place it where it will be exposed to a normal cycle of day and night, but out of direct sunlight. Good luck, let me know what happens!

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  12. Larva specimen found on Manitoulin Island in Ontario, Canada. August 23.

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  13. Larva found today 9,000 ft altitude, 2 hrs west of Ft. Collins, Colorado.

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  14. Just found one on my garage trim... Bayside, NS
    Close to Peggy's Cove
    Haven't seen one before.

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  15. My 8yo daughter found one and he has cacooned himself already. She thinks that he needs to have a "winter." How do we take care of this thing? We are in Iowa. We were going to let him go, but then he made the cacoon so now we are in it for the long haul.... Any help would be appreciated! Thanks!

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    1. Hi, Britt: No need to refrigerate, but do put the cocoon somewhere that is exposed to *natural* changes in day and night. It is apparently changes in day length that trigger emergence from the pupa stage. Maybe you have a shelf near a window, in the garage? Natural temperature changes might help, too, or some close approximation.

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  16. I found one of these in my garden a few weeks ago, I`m in the U.K ... Trying to find out what it was, led me to this blog :)

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  17. Saw a female Elm Sawfly today, posted it on iNaturalist. Thanks for the information in your blog!

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    1. Thank you for sharing that!....and you're welcome. :-)

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    2. My son & I found one today in Maine, it's August 1st.. It took me a while to find good information on what it is & how you handle it, so thank you for your weight up about it!!

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  18. Single last instar larva of the Elm Sawfly seen yesterday grazing on hazelnut in Athens, GA.

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  19. I saw one today in Romania and I want to raise it !

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    1. Excellent! Your species there in Europe is actually different. It is the "Birch Sawfly," Cimbex femoratus. Good luck rearing it!

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  20. Hello and thank you for this wonderful, informative site. We're in Gainesville, TX and our neighbor's son brought an Elm Sawfly larva to us yesterday asking what it was. We had just found a Polyphemus Moth caterpillar in our own yard a couple days before so had wondered if this white "caterpillar" was going to become a butterfly or moth (although it did also look a lot like a grub worm). Neat to find out it will grow up to be a wasp. It was found under a large Elm (American Elm?) tree. Our Polyphemus Moth caterpillar was found crawling down our Lacebark Elm (what a surprise that was!).

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    1. Thank you for the compliments; and thank you for sharing your personal discoveries!

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  21. Hey I found that as larvae here in Henrico, va. Just today! How cool is that?

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  22. I had a convex Americana on my patio table yesterday. It has greenish stripes on it's back. Holy cow, huge wasp in a fly's body. In 41 years living in Wisconsin, I have never seen this. My husband has lived here 65 years and never seen one of these.

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  23. Saw everyone's post I live in Iowa and have a Chinese elm by my house so I went out and counted the larva that I could see 54.

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  24. My daughter found one in the larval state today -we live in Yellowknife, Canada. I have never seen anything like it before - what a face!! We both thought it was a caterpillar but the internet helped us identify it as an Elm Sawfly larva.

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  25. Im in Wisconsin and I have 3 ten year old willows in my backyard and there are larvae literally everywhere. Probably about half the leaves on the trees are gone. How do I get rid of them?

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    1. Your willows will easily survive if you do nothing. Also, I never give pest control advice here. The whole point of this blog is to encourage better attitudes, like fascination and appreciations, towards arthropods. Thank you for understanding that.

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  26. The Elm Sawfly larva we found in Yellowknife, Canada has turned into a cocoon (it's being kept in a ventilated container). Amazingly, my normally bug leery daughter who picked up bug from a sidewalk wants to see the what it looks like in the Spring- when it's completed its metamorphosis into the winged state.

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    1. That is wonderful to hear! I live for stories and comments like this, so thank you for sharing.

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  27. A friend of mine found one today (6-19-17) in Mt Rainier Nat'l Park, WA. It was on the hiking path, lethargic(maybe reaching maturity?), they moved it off the path. Pretty impressive size/coloring!

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  28. Found a larvae on a native yellow birch in my backyard today (northeastern PA). Distinctive black stripe on its back was actually a black stripe with a pale blue or pale yellow stripe down the middle when viewed through a magnifying lens. Amazing how detailed this little guy is! Thank you for helping me figure out what the mature form will be. Great site.

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    1. Thank you for the compliments, and for sharing your observation!

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  29. I found one on my shed door handle yesterday. Thanks to you I found out what it is. My neighbors have many over grown miniature elm bushes that are very unsightly and messy in my yard! Not to be mean but I'm hoping they eat all those elms! Those trees should have been cut down 10 yrs ago. Eat on baby wasp! :-)

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  30. Thank you for this detailed description. Found two of the larvae curled up and sleeping on the underleaf of two different hop-hornbeams at water's edge one early Sept. morning in Central Ontario, Canada. They had been feasting on the leaves. Do you think the adults could be the reason for sparse foliage on our elm shade tree?

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    1. Hard to say. Elms are pretty tasty to a lot of different insects; and given the time of year, it might be a natural part of the tree's cycle.

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    2. Saw the adult by the lake this week; just beautiful, but it was too quick to photograph.

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  31. Hi Eric, I had what I now understand thanks to google images and your site a nice female Elm Sawfly land on the inside of pickup door 1 hour north of Slave Lake, Alberta on June 25, 2018.

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  32. Found one today in Kenora Ontario. Adult male that looks just like your pic! Thanks for this!

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  33. Found one in the larval stage today in Skagway, Alaska. It was in the process of eating leaves of a cherry tree. Earlier this summer I think we spotted an adult elm sawfly on a birch tree. Neat to have seen both stages in one year, especially since I haven’t since them here before.
    Thanks for the decription and photos you’ve provided.

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  34. ok- this may be terrible but we had probably thousands of these caterpillars in our grove this summer in our hybrid willow trees. And now, nearly all of our leaves are gone except the very tops- the caterpillars ate all the leaves! How do I get rid of these things??

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  35. Found one in the grass in Vermont today. Never have seen one here in Vt.

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  36. My daughter found a larva in July 2018 and after few days has turned into cocoon. And today it has hatched to insect, what I never saw.
    Google helped: and it is very likely Elm Sawfly Cimbex americana.
    Locatin: Europe / Slovakia / city: Bratislava

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  37. Found one today in Allen TX. The larva was fascinating to watch. What a beauty and it lifted my spirits to find it. So glad I had my camera with me. Great shots. Thank you for your website. We teach our kids to love all creatures large and small. Also, wish for people to use less chemicals, protect our waters, air, see the beauty in weeds, and insects. They make our world healthy. K.

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    1. Aw-w-w, thank you for sharing this comment, and doing what you do!

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  38. Just saw some larvae in a river birch tree. Some in cocoons and some crawling on the ground in louisiana.

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    1. Here in Bastrop, TX, I noticed these elm saw fly larvae are all over my river birch trees last year, and they came back about a week ago. In fact one just landed on my hat as I was sitting under the tree. As they are large, it's a pretty scary surprise. Anyhow you just helped me identify it, thank you.

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    2. Found this one in Regina, Saskatchewan June 10,2023

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  39. Saw my first one in the UP of Michigan on July 6. Now that I know what it is I'll keep an eye out for more.

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  40. Saw one Jul 20 where the spectacular yellow stood out on the grey road. We moved it to the bush line so it wouldn't get squished by a car, and saw the coiling response. Kenora, Ontario, near the Ontario / Manitoba border, on Lake of the Woods.

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  41. Found one today. Wasilla, Alaska

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  42. I just saw one of these at my weekend trailer in McDonalds Corners, Ontario. I have some cool pictures of it, but I don't think I can post them here.

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  43. Husband brought one in that was crawling on his vice in the garage.It is close to 2 inches.
    If I wish to keep and share with the grandkids...what shall I do to feed it and support its cocooon process.

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    1. If it was off of a plant then it is looking for a place to spin a cocoon. Simply place some twigs in a jar and place the larva inside.

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  44. I found a sawfly larvae near a willow in my yard in the Kootenays in Southern British Columbia. I had never seen such a creature before , bright yellow with a black stripe and almost white head. He is so cute . I have named him Clyde and was able to ID it thanks to others on the Farm the Kootenays site. I put him in a jar with willow leaves and branches and 2 days later it was a coccoon . Didn't realize it will take so long for it to become a fly ... guess I don't really have to keep watch over it every day ;) I will not destroy it as it would take some doing for future larvae to survive the crows and skunks that mine my yard . Thank you for all the info .

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  45. I have seen this sawfly in Wetumka, Oklahoma. I thought it stung me, I put it in a jar, Did a little research, came up with nothing, tossed jar and now apparently I was mistaken. This was 3 years ago. Thanks for the info.

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  46. Have a birch completely stripped clean by the caterpillar form outside of houston tx. Loval forestry say they do significant damage to the trees. They gorge themselves from the leaves and then drop to the floor. Very beautiful in form. Normal insecticide work well, and or labs love eating them.

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  47. Bug Eric, thanks for your informative post. Saw an elm sawfly on acreage 20 miles east of Houston TX on April 16 and a larvae the next day.

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  48. Update to the elm sawfly larvae dropping on me in Bastrop. I researched more and found that they are all over my Elm trees, so that makes sense. Not sure if my Elms are either American (River) or red. Anyhow, I had to move inside due to the incessant Elm Sawfly Larvae bombings. Apparently they are not too tasty to my dogs either- I suppose its the toxin release.

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    1. Thank you for sharing your experiences! This is why I write this blog. :-)

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  49. Thank you for posting! I’m located in Houston, TX and found one on our Japanese maple. I thought it was a caterpillar but it’s an elm sawfly large:-)

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  50. We found one last night, May 25 2020, on our front porch. Thought it was a caterpillar, but did a little research. It coiled for a bit but finally started moving around. My boys have named it Mr. Caterpillar. How long does it stay in larvea form? What does it like to eat?

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    1. The blog post itself tells you what they feed on....but if you just found it crawling around then it is done eating and is looking for a place to spin a tough, leathery cocoon.

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  51. Love to share photos if you'd like. 🐛🐛🐛

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    1. I appreciate the thought, but no thank you. I do not receive images from people I don't know.

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  52. From Saskatoon, SK. Scared myself running across a large male who had just emerged on May 29th. Had some trouble identifying it. Thanks for your post :)

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  53. Puslinch On, (40 minutes west of Toronto). Found a handsome male lying in the grass. His wing has been damaged. He is a big boy for sure.

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  54. I found a large adult wasp yesterday here on Vancouver Island, BC. It scared me it was so big, about an inch and a half (7 cm). It was very yellow striped on the back end of it. I sent a picture to our invasive species sight as we have had some Asian Giant Wasps showing up here in the last few months. They said it was an Elm Sawfly. I'm still amazed at how big it is.

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  55. My grandkids spotted one on the shore of Gardner Lake in East Machias, ME. No one had seen one before 😳. The boys were very excited, but the rest of us will be fine if that is our only lifetime sighting!

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  56. We saw two big elm sawfly larva/caterpillars today pigging out on leaves in Northern New York. They were so big! One curled up for a nap which was fun to see. Love seeing new things in the woods, and learning the names of our discoveries. Appreciate your information about them so I can share with my curious kids. ���� Nature is the best��

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  57. Our Austrees are covered in the grub like form. So many! And they are stripping branches completely. Located in Iowa.

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  58. Thanks so much for your post I didn't know what I was looking at. I was looking under caterpillars but as I found out it's not. Seen one in Temagami, Ontario.

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  59. My 6 year old found two larvae this week in Nome, Alaska

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  60. I trapped this one in my yard yesterday in Saskatoon. Appwars to be a healthy male sawfly. To bad I can't post photos.

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  61. I have one. Flew out of tree in my backyard. Stayner Ontario

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  62. I'm just found one. Northern part of Nova Scotia Canada. He was chilling around my garden and I put him in my flower bed. Seems pretty docile.

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  63. Found a larvae under our elm amd maple trees. Northern Illinois

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  64. We first noticed that we had a problem with the elm sawfly about 3 years ago. At that time our willow tree almost died. They ate most the leaves on it. We ended up finding a professional that came n gave our tree an injection. It helped but we still see them every year and just try to get rid of the larve. Do you have any suggestions on how to get rid of them? Central Wisconsin

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    1. First, I am sincerely sorry that you have had this experience. That is an exceptional scenario, certainly not the rule (that sawflies can defoliate and kill trees). That said, if you follow this blog you know that I NEVER suggest "how to get rid of" ANY insect or spider or other arthropod. Thank you for respecting.

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    2. I'm in Ripon. Are you far from me? I found a larvae for the first time on my corkscrew willow today.

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  65. Took some internet searching but found your site. The Elm Sawfly was attaching a large dragonfly and ended up in our pool. Didn't know what it was and was concerned it was a murder wasp. British Columbia Canada.

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  66. Found one walking across my path . Never seen before . No idea what to do with it . Thunder Bay Ontario Canada . 35 feet away from Lake Superior.

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  67. Found one on my lawn chair today. Quite large. Never seen one before. Norway Bay, Bristol, Quebec

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  68. My grandchildren found two adults who had been enjoying some "adult time". This was about an hour ago. I'd never seen one before so I had to figure out what they were. Regina, Saskatchewan, Canada

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  69. Moose Jaw, Sask, Canada,..just spotted this creepy crawler on my deck

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