When is a locust borer not a locust borer?
June 7, 2010 19 Comments
…when it is a hickory borer!
The hickory borer, Megacyllene caryae, is perhaps the most frequently misidentified beetle in eastern North America due to its almost perfect resemblance to the closely related locust borer, M. robiniae. Unlike the latter species, however, which is encountered abundantly during the fall on flowers of goldenrod (Solidago spp.) and attacks living black locust (Robinia pseudoacacia), the hickory borer is active only during the spring and breeds in the dead wood of hickories (Carya spp.). Adults emerge from the wood as soon as temperatures begin to warm in early spring, a fact which causes it to be most frequently encountered during winter when it emerges indoors from firewood brought in from outdoors. Many times this causes the alarmed homeowner to post a photo of the insect on BugGuide and ask if it will cause damage to their home. So close is its resemblance to the locust borer that novice insect enthusiasts often identify it as such based on comparison to photos and refuse to believe it is not that species, even when told otherwise.
Of course, there are distinguishing characters that, with a little practice, become quite obvious – the legs of the hickory borer are often distinctly reddish (as seen in the above photo), and the bands of the elytra will many times show an alternating pattern of yellow and white (not quite so apparent in the above photo). The elytral bands are also slightly narrower and often broken and incomplete in this species, while in the locust borer they are wider and nearly always extend completely across the elytra. Lastly, the pronotum of the locust borer is narrowly margined with yellow on the anterior edge, while in the hickory borer the anterior margin is black. That’s a tough character to see without magnification, and all of these characters really are only necessary when examining specimens in a collection (and even then only if there is no date on the collection label). Season is the easiest distinguishing character – if it occurs during spring it is the hickory borer, and if it occurs during fall it is the locust borer. There are several other species in the genus that can be confused with these two, but they do not occur in eastern parts of North America.
Photo Details: Canon 50D (ISO 100, 1/250 sec, f/14), Canon 100mm macro lens, Canon MT-24EX flash (1/4 ratio) w/ Sto-Fen diffusers. Typical post-processing (levels, unsharp mask).
Copyright © Ted C. MacRae 2010