Ovipositing Pigeon Horntail

Tremex columba (pigeon horntail) | Wayne Co., Missouri

Tremex columba (pigeon horntail) | Wayne Co., Missouri

By early July, woodboring beetle activity is at its peak in southern Missouri. Even though many of the smaller species of jewel beetles (family Buprestidae) and longhorned beetles (family Cerambycidae) have already come and gone, bigger species in genera such as Buprestis, Acanthocinus, Enaphalodes, etc. are ripe for the picking. All one has to do is travel for hours to high-quality forest (upland or lowland—either is fine depending on what you wish to find), hike for additional hours through stifling mid summer heat and humidity, and carefully search the trunks and branches of any declining or recently downed tree (don’t forget to look along the undersides) while dodging deer flies (if ever a creature sprang from the pit of hell!) and slapping mosquitos! Sure, you can cheat and just drive along National Forest roads looking for recent logging operations—it’s a good way to get large series of common, widespread species; however, if you want to get the good stuff you’ve got to seek out the high-quality forests—those not managed for timber—and look for declining trees and natural wind-throws.

Of course, not all wood borers are beetles. Among the more spectacular non-beetle wood borers are the horntails (order Hymenoptera, family Siricidae), represented in this post by one of its more commonly encountered species, Tremex columba (pigeon horntail). That is not to say that they are frequently encountered, at least in my experience, but I do remember the first time I saw one of these as a boy. I knew in my heart that they were harmless—my already tattered copy of The Golden Guide to Insects said so; yet I could not bring myself to actually grab what would become the latest prize specimen in my insect collection with my bare fingers, instead sneaking a jar over it and sliding the lid underneath.  I’ve seen them a few times since, but until recently I had never seen what must be considered their most remarkable feature—the ability to thrust a needle-thin ovipositor several cm into solid wood! While hiking the Shut-Ins Trail at Sam A. Baker State Park last year, I spotted a large, recently wind-thrown tree off the trail and picked my way over to see what woodboring beetles I might find. As I approached the horntail in these photos took flight, but I stood still and watched her settle back onto the trunk and resume searching activities. Using all the stealth I could muster, I made my approach—hoping to get at least one good shot of this spectacular insect. I would have been happy if I had walked away with nothing more than the first photo in the sequence below. What happened next, however, was icing on the cake. As the remaining photo sequence shows, she suddenly arched her abdomen high and began probing the wood with the tip of her ovipositor, then bracing it at a precise 90° angle relative to the lower abdomen, slowly thrust it deep into the wood until her abdomen was completely level above the trunk.

I never cease to be amazed by insects, but sometimes their capabilities just seem incomprehensible. If you disagree, just imagine trying to insert an insect pin deep into solid wood with nothing but your bare hands (or, more precisely, pushing only with your butt) and see if you don’t change your mind!

Copyright © Ted C. MacRae 2013

16 thoughts on “Ovipositing Pigeon Horntail

  1. Love this series of shots…but no, I’m not gonna try an push an insect pin into solid wood with my butt. Way too much skill involved, lol

        • Thats a mild version of what one salty-tongued entomology professor I had used to call Megarhyssa.
          Anyway, I once tried to pick up on of these that was not completely inserted into the wood (so I didn’t think that her ovipostitor might be firmly stuck in the medium) and ended up tearing her loose from the end of her abdomen. Senseless violence, for which I have some regret. Oddly, it is my impression that these cannot, or at least do not, use the ovipositor defensively.

          • Yes, but Stumpeffers isn’t appropriate for Ted’s PG bug blog. 😉

            And you are correct – ovipositor does not equal stinger. If they (as in many species of wasps) have an ovipositor, they cannot sting at all – it’s just a big, clumsy, incredibly amazing egg-insertion machine. But I’m with Ted – every fiber of my being won’t let me grab them regardless!

  2. Beautiful photos, Ted. Change of subject! I have a question I’ve been meaning to ask. This fall, in my terrariums, my tiger beetles would sometimes throw themselves to the ground and flail dramatically. Oh my god, was my first thought, they’re having a seizure! I think they were rubbing themselves against the dirt, some kind of grooming behavior. Have you ever seen this?

  3. Very nice series, but at the moment hiking through heat and humidity seems preferable to the alternative outside.

    I always found sweeping a net from back to front over my head a moderately satisfying way deal with deer flies. It is a bit like trying to empty the ocean with a teacup, but looking them in the eyes and then crushing them seems fair turnaround, although no doubt bad karma.


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