Wednesday, September 26, 2012

Wasp Wednesday: Pigeon Tremex Horntail

People who have minimal knowledge of wasps can’t really be faulted for having a startled or panicked reaction when confronted with one of these creatures, especially if it is a large insect. Among the more intimidating of wasps are the horntails in the family Siricidae. They do not sting, but they look like they can. Here in the Front Range of the Rockies, the most common species of Siricidae is the “Pigeon Tremex,” Tremex Columba.

So far, I have encountered only male specimens, resting quietly on foliage at about eye-level. They can be approached easily and closely if you are careful. This is a native species ranging widely from Nova Scotia, New Brunswick and Quebec, south to Florida, and west to Mexico, Arizona, Utah, and Colorado. There are even a few records from southern California.

Siricids in general are more closely related to sawflies than any other wasps. The abdomen is joined broadly to the thorax, giving the entire creature a cigar-shaped appearance. They are about a third the size of a stogie, too. Adult females range from 37-50 millimeters (1.5-2.0 inches). Males average smaller, from 18-37 millimeters. Note that western specimens of Tremex Columba are usually much paler in coloration than eastern specimens.


© Andrew Williams

The females are equipped with what looks like two stingers, one short one protruding from the top of the tip of the abdomen, and another longer, needle-like rod at the bottom of the abdomen. The wasps are, in fact, non-venomous. The top “horn” is called the “cornus,” and both genders possess this spur, which gives the family its common name of “horntails.” I have been unable to find an explanation of the function of the cornus, if there is one. The longer appendage is an egg-laying organ called the “ovipositor.” The female uses this complex part of her anatomy to insert eggs into dead, dying, or weakened hardwood trees. Maple, beech, elm, apple, pear, poplar, oak, hickory, sycamore, and hackberry are all known hosts of this wasp, but other deciduous trees in poor condition are probably utilized as well.

The ovipositor acts like a drill and hypodermic needle. It is housed in a two-part sheath that helps to brace the sawtoothed egg-laying organ as it works its way into bark and wood. Lumberjacks have a vulgar nickname for these wasps, owing to what the wasps appears to be doing when they oviposit into a bole or stump. I’ll leave that epithet to your imagination.


© Andrew Williams

Not only does the wasp lay her eggs in the tree, she also delivers a wood-rotting fungus, Cerrina unicolor to the site of each egg insertion. She stores the fungus in special abdominal glands called mycangia, until she is ready to deploy it. The fungus breaks down cellulose, and both fungus and decayed wood are then consumed by the larval wasp.

Larval horntails are grub-like, and easily mistaken for beetle grubs save for the cornus on the very tip of their worm-like bodies. It usually takes more than one year for the horntail to complete metamorphosis.


© Project Gutenberg (Google)

You would think that a larva tunneling inside a tree or log would be safe from its enemies, but such is not the case. Huge wasps called giant ichneumons can drill down and reach the horntail grubs. One of my most popular blog entries chronicles the life cycle of these Megarhyssa wasps. Yet another kind of wasp attacks younger larval stages of horntails. Wasps in the family Ibaliidae (and genus Ibalia) drill down to reach horntail larvae that are at a more shallow depth.


Female Ibalia sp. © Mark MacMillan/Colorado State University

Pigeon Tremex horntails that survive the perils of youth eventually pupate, emerging as adults most often in late summer or fall. Right now is the ideal time to find them, but you have to look at a lot of dead, standing trees to find them. Horntail species that use coniferous trees as hosts are often attracted to wildfires, since fire often weakens trees. Many wood-boring beetles are also active in the wake of conflagrations.

Please help spread the word that with few exceptions (introduced species like Sirex noctilio for example), horntails are not pests, but merely exploit trees that are already damaged by environmental stress, and/or diseases or other destructive insects. They are important to forest ecology and the average homeowner has no need to control them.

Sources: Cranshaw, Whitney and Boris Kondratieff. 1995. Bagging Big Bugs: How to identify, collect, and display the largest and most colorful insects of the Rocky Mountain region. Golden, CO: Fulcrum Publishing. 324 pp.
Drees, Bastiaan M. and John Jackmann. 1999. A Field Guide to Common Texas Insects. Houston: Gulf Publishing Co. 359 pp.
Evans, Arthur V. 2008. National Wildlife Federation Field Guide to Insects and Spiders of North America. New York: Andrew Stewart Publishing, Inc. 497 pp.
Schiff, Nathan M., Steven A. Valley, James R. LaBonte, and David R. Smith. 2006. Guide to the Siricid Woodwasps of North America Morgantown, WV: USDA Forest Service Forest Health Technology Enterprise Team (FHTET-2006-25). 102 pp.

29 comments:

  1. If you're interested, Nathan Schiff & Henri Goulet (among others) recently published a massive revision of the Siricidae of the Western Hemisphere (including keys and illustrations for all species) in the Canadian Journal of Arthropod Identification:

    Schiff, N. M., Goulet, H., Smith, D. R., Boudreault, C., Wilson, A. Dan, and Scheffler, Brian E. 2012. Siricidae (Hymenoptera: Symphyta: Siricoidea) of the Western Hemisphere. Canadian Journal of Arthropod Identification No. 21: 305 pp. (PDF version).
    Published on 6 July, 2012. http://www.biology.ualberta.ca/bsc/ejournal/sgsbws_21/sgsbws_21.html

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  2. Sir I also make blog about insects and i adore your passion. Please visit my site sometime, more power to you sir.

    http://insektosaclsu.blogspot.com/

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    1. Thank you! Just to clarify, CLSU (Central Luzon State University), where Robert works, is in the Philippines. Looking forward to more of your posts, Robert!

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  3. I'm pretty sure I just saw one of these in Portland, Oregon. It would seem that is out of their range but it looked just like this.

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    1. You have another kind of horntail there: Urocerus californicus. I know, I grew up in Portland, but never had the pleasure of seeing a live specimen.

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    2. I have one in northern michigan. Are they normally found here. I have never seen one before

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    3. Hi, Aimee. Yes, they should be found there in northern Michigan.

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  4. Thanks for this terrific information! I just spotted one on a dead weeping birch tree. Are they endangered or do they have healthy populations? It certainly is an impressive creature.

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    1. You're welcome! No, they are not endangered. Quite common, in fact, just seldom noticed. I'll be doing another post soon, as I got video of a female ovipositing.

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  5. Is it possible that this is the creature who is flying among the lavender blossoms along with the bumblebees and bees? He/she appears to be landing on each blossom, then moving along to the next. I'm in Genoa, NV at the base of the eastern Sierra.

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    1. Horntails do not visit flowers. I am not sure *what* they feed on as adults, if anything, now that you make me think about it.

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  6. My dad collected one of these for my son's 4H entomology project. My son was pretty pumped about learning about them and enjoyed reading from your article Very informative.

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    1. Thank you so much for the compliment! I have a more recent post built around a video of a female horntail ovipositing (laying eggs). You can click on the "wasps" category in the upper right corner of this page to quickly scroll to that post.

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  7. We just found two of these in Ottawa, Canada in our back yard in the city. Never saw one before. Quite intimidating looking. I have a picture if you wish to see it.

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  8. Hi Bug Eric! Thank you for the very great information on the Pigeon Horntail Tremex. For the first time in the 24 years I have lived in Colorado Springs, Colorado, I found (from IDing your site and others) two in my backyard. Since the dogs were trying to eat them I thought they were wasps, I squished them and tossed carefully. I'm very sorry now as they seem to eat the rotting hard wood from a tree we had cut down 5 years ago. My friend just found a dead one in her yard and I was able to tell her all about them. But the question I have for you, is, the ones I killed were at least 4 inches long, hers was only about 2. Could mine had been their natural enemy, the giant ichneumon wasp?

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    1. I'd have to see the specimens to be sure of what you killed...but I do have a post on giant ichneumon wasps, too. The differences between the two are obvious. Female giant ichneumons have an ovipositor (whip-like appendage at the rear of the abdomen) that is over two inches long by itself.

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    2. I just found one on my patio tonight in Kingston, ON.

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  9. Thank you for writing this article. This morning we (my children ages 9, 7, and 4)found one of these in our yard in Littleton, CO. We had no idea what it was until I found this post via google. What an amazing looking creature. The children are busy drawing it in their nature journals. Ours is a female.

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    1. Thank you! I live to hear stories like this....Also, I have a newer post with a video of a female ovipositing....http://bugeric.blogspot.com/2015/09/pigeon-horntail-wasp-ovipositing.html.

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  10. I used to run into either these critters or a close relative of theirs in the coastal mountains of British Columbia. I remember being terrified as a youth by their large size and apparent two different kinds of "stingers".

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  11. Hi! I have found something similar to these, like the cigarshaped abdomen going into the thorax, but they are only about 0.5in long. Is it also a type of tremex? They are in my house and a dying tree in our backyard.

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    1. They would have to be something else, maybe Xiphydria sp.

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  12. Hello eric! Thank you for this blog. I've been searching to find the identity of our strange guest today. I think it's a female, and I think she was trying to lay eggs in my screen!
    I saved a video on my phone of it and I'd love to get your take on it. Could I send it to you via cell message or email?

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    1. Best to upload it to YouTube, and then e-mail me the link, or share it here.

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  13. Hi Eric,
    Thanks for the info! We are in SE Ohio. I was making some log lights. Hollowing out some dried elm firewood, with a chainsaw, basically. It's a project for my grandson's wedding.
    Anyhow, I had seen some small holes in the tops. As I was cutting the inside out of these logs, the insects were trying to back out into the void. A couple backed out, and I wasn't sure what I had. So, I collected them in a jar, until I identified them. Now that I know they aren't a threat, to the trees, or me, I'll let them go.

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    1. Thank you for sharing your story; and congratulations to your grandson on his wedding!

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  14. Seeing the previous comment from Ohio posted within the past couple weeks, I wanted to add that yesterday (Oct 7) I collected a female Tremex from a silver maple in SW Ohio in a little park near the Whitewater River just NW of Cincinnati. I grabbed it by the thin part of its ovipositor to pull it from the tree. I stopped by your website to see if anything was known about feeding habits of the adult (if any) but I see nothing is known. I used to find these in the elm trees in Ithaca NY "many" years ago while I was an entomology undergrad at Cornell.

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    1. I lived in Cincinnati from 1988-1999, and saw few of these. Fewer by far than I have here in Colorado....A good many insects live as adults on the fat they accumulated in the larval stage, never feeding as adults. That said, I would not be surprised if horntails fed on sap from tree wounds.

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