In eastern North America, autumn is the beginning of the end for most insect groups. Preparations for winter are either complete or well underway—eggs have been laid, nests have been provisioned, and larvae (hopefully) have eaten well enough to endure the long, cold months that lie ahead. But for a few insects, fall is just a beginning. Triggered by cooler temperatures, shortened daylength, and invigorating rains, adults of these insects burst forth under crisp, blue skies to feed amongst a plethora of fall flowers or prey upon other late season insects before the advancing cold, finally, forces a close to the season. As a beetle man, my favorite fall insects must be the “fall tigers” (i.e., tiger beetles) that come out in force and zip across barren sand dunes or bask on exposed rocks of dolomite glades. My fall insect collecting focuses almost exclusively on these insects, since my other favorite groups (jewel beetles and longhorned beetles) are, for the most part, restricted in their adult activity to the spring and summer months and long gone by the time fall rolls around. There are, however, a few longhorned beetles that buck the normal spring/summer rule for the family, namely species in the genus Megacyllene. The most commonly encountered of these is Megacyllene robiniae (locust borer), and anyone who has examined goldenrod (genus Solidago) and its profuse blooms during the fall has likely encountered this familiar beetle with its narrow, alternating, zig-zag bands of black and yellow.¹ I have seen this species many times and in many places; however, I still always enjoy seeing it anew in the field each fall—perhaps as some sort of confirmation that the fall season truly has arrived.
¹ If you see a “locust borer” in the spring, it is actually the closely related Megacyllene caryae (hickory borer), while further west in the Great Plains during fall you might find Megacyllene comanchei.
Another species in the genus that is far less commonly encountered, however, is Megacyllene decora (amorpha borer). I have encountered this stunningly beautiful species in only a handful of locations in Missouri (MacRae 1994)—all where stands of its larval host plant, Amorpha fruticosa (false indigo), grow in association with goldenrod and snakeroot (genus Eupatorium). These sites are primarily in the big river valleys of the state (Missouri and Mississippi Rivers), although I have found at least one site in the prairies of west central Missouri. Earlier this summer while traveling through the southeastern lowlands of Missouri, I noticed a stand of native Hibiscus growing within a wet ditch along the edge of a small city park and stopped by to look for the even rarer Hibiscus-associated jewel beetle, Agrilus concinnus (MacRae & Nelson 2003, MacRae 2006). While I did not find that species, I did notice fairly good numbers of A. fruticosa plants along the edge of the ditch as well and young goldenrod plants that had not yet reached flowering stage. At that moment I knew I had a good potential site to look for M. decora and made a mental note to stop at the site again later in the season when goldenrod began to bloom.
Last week I returned to the site to find not only goldenrod in its earliest stages of bloom, but an even greater number of Eupatorium serotinum plants already in bloom. I wanted to photograph the beetle, of course, but what I was really hoping for was to find and photograph the beetle on the stems of its Amorpha host plant (I have only seen this once before—all other sightings of the beetle have been on flowers of goldenrod and snakeroot). I approached each Amorpha clump cautiously and searched the stems carefully, also keeping an eye on the goldenrod and snakeroot blooms as I moved from one clump to the next. After searching a number of clumps, I finally found the adult shown in these photos. Fortunately, I knew from previous experience in collecting these beetles that they are not a particularly wary species (few aposematically- or mimetically-colored beetle are), so I was able to get a number of good photographs before I (stupidly) bumped the beetle with the diffuser over my flash heads and disturbed it.
It would be another half hour before I would find a second beetle, and in total on the day I saw only three (all on Eupatorium). This and the very early stage of the goldenrod blooms suggests to me that the beetles were just beginning to emerge—over the next few weeks I am sure they will become more numerous at the site, so I may yet have an opportunity to photograph one on its larval host plant when I pass by the area in a couple of weeks.
MacRae, T. C. 1994. Annotated checklist of the longhorned beetles (Coleoptera: Cerambycidae and Disteniidae) known to occur in Missouri. Insecta Mundi 7(4) (1993):223–252.
MacRae, T. C. 2006. Distributional and biological notes on North American Buprestidae (Coleoptera), with comments on variation in Anthaxia (Haplanthaxia) viridicornis (Say) and A. (H.) viridfrons Gory. The Pan-Pacific Entomologist 82(2):166–199.
MacRae, T. C., and G. H. Nelson. 2003. Distributional and biological notes on Buprestidae (Coleoptera) in North and Central America and the West Indies, with validation of one species. The Coleopterists Bulletin 57(1):57–70.
Copyright © Ted C. MacRae 2012
11 thoughts on “A classic fall ‘bycid”
No doubt it’s a beautiful longhorn. It must come in handy knowing where to look for what while looking for beetles. I’ll be headed out doors this weekend, but I have no idea what i’ll find, if anything! 😉
Years in the field my friend… years in the field.
That is a beautiful beastie. I wonder if it lives at SNR, which would certainly seem to have the right habitat.
Please go look for it! 🙂
Reblogged this on Animal Lovers' Blog.
Just found my first Amorpha borer on goldenrod on our little 10 acre patch in south central Kansas. How specific is this species in its choice of larval plant? Several folks/sources on the web have mentioned Amorpha fruticosa as its larval food source – would it also be feeding on Amorpha canescens?
Larvae feed only in Amorpha fruticosa, at least as far as is known. Full grown larvae are almost the same diameter as the stems of the plant, so size alone makes A. canescens (a much smaller-stemmed species) an unsuitable host plant.
Thank you for your response. Insects in Kansas reports that they will eat the living crown of “Amorpha species,” leading me to wonder about the lead plant. I do have both species within a couple hundred yards of where I saw the borer.
Many general references will specify only genera for host plants to reduce text and avoid specifics, but the only larval host recorded in the primary literature is A. fruticosa.
It is an incredibly impressive beetle, itn’t? 🙂
Thank you for your help! You’ve relieved my mind a great deal, as I only have a few (remnant) plants of leadplant left in my overgrazed pasture/restoring prairie and I’d like to see them thrive and reproduce!
Yes, this is a gorgeous beetle. I’m so glad that I saw it and was able to i.d. it relatively easily.
I’m excited to have found your blog and look forward to learning quite a bit as you share your adventures.
Megacyllene decora is such a spectacular beetle, shown beautifully in your photos. It must be exciting to find one on flowers. I have seven species of Megacyllene in my collection, including a special one – Megacyllene powersi (found in the Dakotas), first collected by my late friend and entomologist Jack Powers. Linsley and Chemsak named the species after Jack in 1963.