Ovipositing Pigeon Horntail
January 6, 2013 16 Comments
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