North America’s most recognizable longhorned beetle

One of the more impressive insects that we found during our visit to Sand Hills State Park in south-central Kansas last June was Plectrodera scalator, the cottonwood borer. Large and robust (in fact, the only larger species in the family are the prionid root borers and their kin), their striking checkered pattern of white pubescence on a glossy black body makes them perhaps the most recognizable of all North American longhorned beetles (Linsley & Chemsak 1984). The very robust body of this individual, along with the relatively shorter antennae (only about as long as the body) identify it as a female—males are generally smaller and less robust with the body slightly tapering and the antennae distinctly longer than the body.

Plectrodera scalator

Plectrodera scalator (Fabricius, 1792) | Sand Hills State Park, Kansas

The white coloration on the body of these beetles is not a cuticular pigment (which is rather rare in beetles and is most often associated with species found in white sand habitats, e.g., certain tiger beetles), but instead a result of dense mats of microscopic white setae. The patterns formed by these mats are apparently as unique to each individual as fingerprints are to humans (Yanega 1996), making these beetles at once immediately recognizable as a species yet distinctive as individuals.

Plectrodera scalator

Adults of this species are found most often on cottonwood.

These are said to be common beetles in their range across the eastern two-thirds of the country, especially so in the Great Plains where their favored host, cottonwood (Populus deltoides), is especially abundant. Despite this, I have encountered this species only a handful of times in more than 3o years of searching. I know they’re out there, even in my home state of Missouri where I recorded 154 specimens collected in the state and deposited in various collections (MacRae 1994). It was not until around 2000 that I even saw my first ones (on a cottonwood tree in a homeowner’s yard just across the Mississippi River in Illinois), and in fact this one was actually found by Mary Liz Jameson, who had accompanied us to the field that day. It makes me wonder if their coloration, so strikingly conspicuous when isolated against a clean, blue sky background, might actually afford some type of cryptic protection against the normal backdrop of foliage and branches on which they are normally found—a phenomenon that I call “conspicuous crypsis” and which I have noted for other longhorned beetles (e.g., Acanthocinus nodosus). Perhaps, with this species at least, I have not yet set my search image to notice them.

Plectrodera scalator

Large, robust size and a distinctive checkered pattern of black and white makes these beetles among the most recognizable longhorned beetles in North America.

REFERENCES:

Linsley, E. G. and J. A. Chemsak. 1984. The Cerambycidae of North America, Part VII, No. 1: Taxonomy and classification of the subfamily Lamiinae, tribes Parmenini through Acanthoderini. University of California Publications in Entomology 102:xi + 1–258. [preview]

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. [pdf]

Yanega, D. 1996. Field Guide to Northeastern Longhorned Beetles (Coleoptera: Cerambycidae). Illinois Natural History Survey Manual 6, x + 174 pp. [preview]

About Ted C. MacRae

Ted C. MacRae is a research entomologist by vocation and beetle taxonomist by avocation. Areas of expertise in the latter include worldwide jewel beetles (Buprestidae) and North American longhorned beetles (Cerambycidae). More recent work has focused on North American tiger beetles (Cicindelidae) and their distribution, ecology, and conservation.
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17 Responses to North America’s most recognizable longhorned beetle

  1. Cosmin Manci says:

    nice one … in many lamiinae (I’m thinking to our Saperda) is easier to get them from larvae than to find adults. So maybe is the same there? Also here normally maybe I find few Saperda specimens in a year but rarely are those moment when all horoscope meet and you find a bottle of a certain species that you have never seen or only seen it once🙂 .

  2. Mike Baldwin says:

    Very interesting – I’m fascinated by the mats of white setae that create unique patterns. Are there other possible purposes besides cryptic protection?

    • Most lamiine cerambycids make extensive use of colored setae on their bodies. I can only imagine that it must have a visual function, which seems to suggest avoiding being seen by predators.

  3. Adrian Ruicanescu says:

    Beautiful beetles you have there.

  4. mn nature says:

    Think of these like emerald ash borers as destructive but you capture this cottonwood borer in a new light. It is quite beautiful. Awesome blog and thanks for sharing. -www.MNnature.org

  5. ozarkbill says:

    Great stuff, Ted! This reminds me of a special August day on Ellis Island at RMBS, when I must have been fortunate to see a hatch of these guys, or something. I remember being bombarded by more than a dozen. Giants. Like being within a helicopter raid. Of course, I only had the bird lens that day.

  6. Mark Sturtevant says:

    One of my favs in the coleoptera. As for whether their coloration serves as a kind of camouflage against predators, in this case I think we need to consider what they look like to predators. I am not sure, but don’t birds see in the UV or IR?
    Many years ago I came across dozens of these hanging on cottonwood saplings alongside a river.

  7. Robert Wrigley says:

    Hi Ted. My first experience with the beautiful Cottonwood Borer was on 23 July 2003, on the Arkansas bank of the Red River, 9 miles south of Foreman, along Highway 41. On a 90-degree day, I and two companions were hunting for insects when we found literally hundreds of individuals of this species feeding and mating in cottonwood and willow saplings (with mature forest nearby on higher ground). Most beetles were at eye level, and so collecting was like picking plums in an orchard. They were so preoccupied that few flew away. They must have emerged recently from the sandy soil, since the bodies were fresh, without scratch marks, and with every individual sporting its own distinctive pattern of white and black. It was one of the most-exciting experiences I have had in my 25 years of studying and collecting insects. I have picked up occasion specimens in other states, but nothing like that day along the Red River. I returned there several more times and found the diversity of insect life at this spot marvellous, if the river was not in flood stage. Night-lighting along the sandy shore brought out an entirely different fauna (tiger beetles and ground beetles in particular). Thank you for highlighting the Cottonwood Borer. Robert Wrigley

  8. Mike Motto says:

    “The patterns formed by these mats are apparently as unique to each individual as fingerprints are to humans (Yanega 1996), making these beetles at once immediately recognizable as a species yet distinctive as individuals.”

    Beetles are absolutely the best. So cool.

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