The Bug Geek

Insects. Doing Science. Other awesome, geeky stuff.

Photo Friday – A horned beauty

I’m still not entirely sure how this little fellow caught my eye – he was resting on the rough bark of a maple tree, blending almost perfectly.

Maybe he sneezed, or something.

Either way, he’s probably one of my favorite finds of the summer, partially because it’s a “new-to-me” species, and partially because…well, just LOOK at him:

Bolitotherus cornutus (Forked fungus beetle) 1

Male Forked Fungus Beetle, Bolitotherus cornutus

Is that not one of the most adorable little faces you’ve ever seen? The little upturned “nose”! But the fancy adornments on the thorax of this male forked fungus beetle (Bolitotherus cornutus) are what makes him stand out from the crowd:

Bolitotherus cornutus (Forked fungus beetle) 4

These Darkling beetles (family Tenebrionidae) like to hang out on shelf fungi on maple and poplar trees, and are mostly active at night. Only the males sport these fuzzy-tufted “horns”. I have scoured the literature and can’t find a single conclusive answer for their purpose. I suspect they’re partially for fighting with or expressing superiority over other males, but the hairs suggest some kind of sensory function. I really don’t know, and would love it if anyone could shed some light on these structures.

Bolitotherus cornutus (Forked fungus beetle) 3


An another note, I just wanted to tell you that I’m on the Entomology conference circuit for the next two weeks! I’ll be attending and speaking at the Entomological Society of Canada and the Entomological Society of America meetings. If any of you are coming, I’d love to know! Send me a tweet at @GeekInQuestion 🙂 (Also, once these talks are finished, I’m going to FINALLY get around to updating you all on my research a bit – it’s been a productive couple of months!)

14 responses to “Photo Friday – A horned beauty

  1. Brigette November 2, 2012 at 10:14 AM

    I don’t know about the function of the horns, but did you know that they have some really funky courtship rituals? The males have a set of ridges on the underside of their last two abdominal segments that they rub against the female’s pronotum… it makes a scratching sound, which they do for a while before turning the right way around to mate. I’ve gotten SEM images of the structures and a friend of the lab has gotten videos of them going at it (at night, only, with a night-vision camera). He’s got pics here: 🙂 (and I’m jealous of everything you’re doing!!! My life is at a stand-still as my general exam approaches…)

    • TGIQ November 18, 2012 at 7:40 PM

      Wow, that is VERY cool! Fantastic series of photos. Thanks so much for sharing these, Brigette!!! I hadn’t noticed the setae on the underside of my specimen, so that was great to see also 🙂

  2. Ted C. MacRae November 3, 2012 at 10:13 AM

    The male-only armature with densely hairy undersides reminds me immediately of the dynastine scarabs, which in all species studied to use their horns as weapons in male competition over reproductive access to
    females. It seems reasonable that the hairs would serve some sensory/tactile function, and this poster at the upcoming ESA meetings seems to support this.

  3. Stan Malcolm November 7, 2012 at 4:19 PM

    The horns are used by males in combination with a “forked” projection of the clypeus to joust with other males. Lots of work published on their social behavior by Vince Formica. I’m working on a publication describing courtship behavior in detail, including what I call “collaborative stridulation” – the only case I know in nature that requires a male and female together to produce sound. Brigette shared a web page I put together last year as I became interested in these beasts. You can see the video I’m using as a basis for my publication here: Turn up the sound and listen carefully.

    • TGIQ November 18, 2012 at 7:44 PM

      Oh wow, those were your photos? What a fantastic series! They beautifully capture so many fascinating aspects of this animal’s natural history. Thanks for making those available to the general public! I only had a short time with this one subject, but I’ll be keeping my eyes peeled for them in the future so I can witness some of this first hand.

  4. Stan Malcolm November 7, 2012 at 4:48 PM

    See Liles 1956 for basic life history and brief mention of stridulation. (;jsessionid=F61A50AE2B9B17BA3FFCF2163BD5934E?sequence=1) Note too that these beetles, like other Tenebrionids, have eversible terminal abdominal scent glands used as a defense. Eisner etal discussed them in “Secret Weapons…” The glands are everted in response to mammalian breath. See: I’ve observed the males carrying these secretions forward on the legs to setal patches further forward on the body – spreading the wealth. Too much to say about these fascinating creatures; they continually surprise me!

    • TGIQ November 18, 2012 at 7:45 PM

      Interesting that the glands are everted specifically in response to mammalian stimulus. Are they ever everted in intraspecific confrontations?

      • Stan Malcolm November 18, 2012 at 10:01 PM

        Not to my knowledge (or observation). However, males do defecate over the female’s head during courtship. This can be seen in the video I linked above in conjunction with the stridulation. “Why” as usual is the tricky question; perhaps there’s a scent component to the poop that implies fitness?

        • TGIQ November 19, 2012 at 8:01 AM

          These might be the most interesting beetles I’ve ever come across.
          Thanks for sharing all this great information!!! I’ll definitely be taking the time to look for them again.

          • Stan Malcolm November 19, 2012 at 8:15 AM

            They’re quite common on the right fungi (big woody brackets of several species). Just look for the oviposition sites (a small oval of fungus goo covering an egg – they’re pictured on my web page linked from Brigette’s post, above). The fungus without evidence of egg laying is the exception. The beetles will usually be on the undersurfaces or in crevices during the day. Larvae and sometimes adults will be inside the brackets. Try not to wipe out a colony. These beetles live up to 7 years as adults so you would be doing significant harm. (Their longevity on a finite resource – a downed tree – may explain the development of such elaborate social behavior; or the development of the behaviors may have favored long lifespans?)

  5. Boletivorus November 13, 2012 at 8:09 PM

    Any chance that these funky setae are for “pollination” of tasty fungus? Pick up excess spores during feeding, distribute them into crevices in wood during diurnal hiding?
    Based on all the much better evidence as to sensory and/or sexually selected fighting and display functions, as well as the fact that shelf fungi seem able to disperse their spores just fine on their own, this seems really unlikely. But hey, why not throw the idea out there!
    Thanks for the post.

    • Stan Malcolm November 16, 2012 at 5:07 PM

      Interesting idea, but as you say, unlikely. The adult beetles’ bodies quickly get covered with fungus goo but the setae remain clean. Besides, the beetles aren’t keen on dispersal; and when they do travel, it’s to other fungi not logs needing inoculation with spores. My best guess is that the setae help the males gain purchase on their rivals during jousting. I don’t particularly like that idea, but so far I have no better one.

    • TGIQ November 18, 2012 at 7:46 PM

      That’s a pretty neat idea! I’ll happily defer to Stan’s expertise on this one, but it would be great to conclusively determine their actual function!

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