Diminishing Stag Beetle

This past June I made a couple of trips to north-central Arkansas. They were my first real efforts to collect insects in Arkansas, despite hundreds (literally) of trips to various localities throughout the Ozark Highlands in adjacent southern Missouri. The similarities between the two areas were obvious, yet there was also the feeling of a brand new area just waiting for exploration. On the second trip, I found a campground that looked good for blacklighting to see what wood-boring beetles I might be able to attract amongst the surrounding pine/oak-hickory forest. The evening was warm (very warm!) and humid with no moon—typically ideal for blacklighting, but beetles were sparse at the sheets for some reason (perhaps deterred by the obnoxiously unrelenting yells of drunk Arkansans and their out-of-control offspring?!). The evening, however, was not a total loss—at one point an enormous stag beetle landed on the top of the sheet.  It was so big that I couldn’t even fit it into the viewfinder of my camera:

I fiddled with the camera and changed some settings.  I got a little more of the beetle in the viewfinder this time, but it was still just too big:

Additional fiddling with the camera allowed even more of the beetle to be seen:

As I took the photographs, I even began wondering if the beetle itself was actually shrinking:

Eventually, it turned out to be a normal-sized beetle after all:

This is a female of the common eastern North American species Lucanus capreolus.¹  I don’t seem to encounter female stag beetles as often as the males, so this was still a nice find on an otherwise frustrating night.

¹ Two bonus point in the current BitB Challenge session to the first person who correctly explains how I know this.  Overall contenders: here’s your chance to score an advantage as we enter the final stretch in the current Challenge session.

Copyright © Ted C. MacRae 2011

14 thoughts on “Diminishing Stag Beetle

  1. Ted: A somewhat loaded question:
    Are they burning around there, or might the dearth of beetles be attributed to something else?

    Around that same time, I did a blacklighting experience with guests at SNR and had the poorest showing ever at the four sheets, and curiously, an almost identical array of those few species and numbers species at each, no matter what habitat — prairie [burned], forest, river [not burned] — the sheets were facing!

    • No, I can’t blame it on burning. Over the years, I’ve learned that blacklighting success does not always occur under seemingly perfect conditions (on the other hand, conditions must be good for success to occur).

  2. Well, if by “this” you mean the sex, you know it’s a female because a male’s mandibles are much larger and more dangerous-looking. If you mean how you know it is L. capreolus, since all your pictures are of the head end it probably has to do with the head. Most likely the kind of “stepped” appearance of the mandibles, along with the reddish-brown color.

    • “This” refers to the sentence that was footnoted – how do I know this is a female L. capreolus?

      While some of the characters I used are on the head, others are on the pronotum and elytra (both of which are visible in at least one of the above photos). I’m looking for a suite of specific characters…

  3. Not sure what part of “how I know this” you were after. Male L. capreolus seem to have wider spanning, thinner mandibles, more like pincers, even “minor” males where mandibles are less huge. (Size of mandibles varies a lot–I’ve seen quite a few L. capreolus, which is pretty common in my area, and regular in my yard.) Females in L. capreolus (and L. elaphus) have more compact, snipper-like mandibles.
    Differentiation of species. Chestnut color here is right for L. capreolus, as opposed to L. placidus. L. elaphus color is pretty similar to that of L. capreolus.
    More details: L. capreolus has just one tooth on the mandible. L. placidus has two, I think–I’ve never seen it. Female L. elaphus has ~three small teeth on the mandible. Also, labrum in L. elaphus is more pointy/triangular than the rather blunted triangle of the labrum in L. capreolus. (BugGuide images seem to show an even blunter labrum in L. placidus.)
    You can’t quite see it in your photo, but both male and female L. capreolus have femora at least partly yellow, though that seems to vary some–sometimes only base is yellow.

    Like you, I’ve seldom found female Lucanus. Males seem to outnumber females at lights by perhaps 5:1 or more. I’m guessing that males disperse while females stay around their larval home?

    My latest photo of L. capreolus is linked–it clunked into the sliding glass door on my deck the other night. I get a couple every year.

    • Okay, so since you’re the second person who wasn’t sure what “how I know this” meant, I guess I’ll have to take the blame for not being clear. The question was, indeed, “How do I know this is a female L. capreolus?”

      You’ve given some of the more important characters that led to the ID. The labrum on L. placidus is even more distinctly quadrate in the specimens I’ve seen. Also, the elytra of that species are more distinctly punctate/rugose than those of L. capreolus and L. elaphus, and both L. placidus and L. capreolus have the pronotum more punctate than L. elaphus.

      The main point of this exercise was to show that there is often not a single “key” character that says this or that species – a more common situation than I think most people realize. Had the femora been distinctly yellow that would have immediately clinched it, but as you note that can be variable and sometimes necessitates the use of other characters.

      Interestingly, I just found another female L. capreolus this past weekend.

      Okay, so you scarf up the 2 bonus points – too bad these are your first points in the current BitB Challenge session 😀

  4. Hey, thanks, I’ll take bragging rights bonus points wherever I can get them. That’s a nice summary of some more of the characters for separating these, so I learned something.
    I still want to see these things doing battle out in the wild–I’ve only found them coming to lights.


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