Elderberry Borer

2010 January 16

S_ found this rather attractively-colored beetle on our window on July 20, and it was large enough that I just took the pictures without a macro lens in the sunlight, with the beetle on my finger [1]


The combination of black and orange is warning coloration that we have seen before, indicating that this beetle probably is foul tasting and/or toxic.


The long antennae and general size/body shape suggest that it is one of the Longhorn Beetles, and checking around it is pretty clearly the Elderberry Borer, Desmocerus palliatus


Elderberry borers evidently only feed on elderberry, genus Sambucus[2]. They lay their eggs near the base of the plant, where the larvae hatch, bore into the stems (which I gather are hollow), and follow them down to feed on the roots. This can’t be good for the plant, but since elderberries aren’t particularly widely cultivated as a crop, nobody seems too concerned about these beetles.


Since elderberry tend to grow in kind of swampy areas, that’s where you will tend to find these beetles, too. This one probably came from the boggy area on the northern part of our property. Most parts of the elderberry plant (stems, roots, leaves, and unripe fruit) are toxic, containing a cyanide-generating glycoside, so children should not be allowed to play with the plants. In addition, there is a toxic alkaloid in the flowers and unripe berries, but the beetles wouldn’t have access to that part of the plant as grubs. I expect that these beetles concentrate the cyanide-producing compound from their food into their bodies, making them downright dangerous to eat. Hence the warning colors[5].

[1] Something I’ve noticed about a lot of insects, particularly beetles, is that they really don’t like to sit still on flat surfaces, like tabletops. But if they are on a surface that they perceive as rounded (like a fingertip) or irregular (like a window screen), they will often perch on it and stay still fairly happily. So, I should probably swap the graph paper I normally use as a background for a series of screens of known opening sizes, and use the screen openings as a size reference.

[2] So, finding this beetle is a pretty strong indicator that we have elderberry bushes growing somewhere nearby. These plants have edible fruit, I used to collect them for my mother so she could make syrups and jelly out of them, which was very tasty[3]. My next task will be to find some of those bushes.

[3] The fully ripe berries taste fine once they are cooked (the cooking is important to destroy the last traces of the plant toxins, just in case the berries were not completely ripe)[4]. Things made from the cooked berries (like, for example, elderberry wine) are non-toxic. Unless, of course, somebody takes it into their heads to poison it, but that’s true of anything, after all.

[4] So, why would a plant that is otherwise toxic, have non-toxic ripe fruit? Well, the general purpose of fruit is seed dispersal, and elderberry is no different. The fruit tempts some animal (most likely birds) to eat them. The animal then leaves seed-filled droppings at some great distance from the parent plant. As long as the seeds can survive the trip through the digestive tract, it works fine. So, it’s important that the eater of the seeds not die from the fruit being poisonous. Meanwhile, the toxicity of the rest of the plant helps keep it from being eaten, and the toxicity of the unripe fruit keeps it from being eaten before the seeds are viable. This still leaves the question of why any plants have *toxic* fruit, but I understand that this is generally a selective thing: for example, fruits that are best dispersed by birds are sometimes toxic to mammals, but are harmless to birds. A prime example of that is hot chili peppers. Evidently, the chemical that causes the hot sensation in mammals like us, is pretty much tasteless to birds, so they can eat the chilies with impunity. For that matter, many fruits that are toxic to *humans* are not toxic to a lot of other animals. I understand that rabbits can eat nightshade without harm, for example.

[5] After all, what’s the use of being poisonous if your potential predators don’t know it? If you are the most toxic beetle in existence, but you look just like every other beetle, then you are likely to get eaten by accident, and so the whole thing becomes a waste of effort. Or, in other terms:

“Of course, the whole . . . point . . . of a Doomsday Machine . . . IS LOST, IF YOU KEEP IT A SECRET! Why didn’t you tell the world, EH?” – Dr. Strangelove

6 Responses
  1. January 19, 2010

    Given their rudimentary digestive systems, are they feeding on the liquids in the roots or are they really breaking down the roots’ cellulose for food?

    For the photos, you could add the grid as an after effect in Photoshop. Just register your camera with some reference points on a rough surface and you could get a sizing grid in the photo very nicely. Make the grid lines semi-transparent and you could even zoom in on portions and get very fine measurements of body parts.

  2. January 19, 2010

    I don’t know about these in particular, but most wood-boring beetles can’t digest cellulose, or only digest it poorly. The insects that can digest cellulose generally do it using symbiotic microorganisms in their guts, and it’s hard to do that without the ability to get the organisms passed down to you from either your parents or your nestmates (which is how termites do it). Wood-boring beetle larvae don’t really have access to these sources of microorganisms, so they have to make do with chewing up the woody material to break up the cells and release the starches, sugars, and proteins that they contain.

    I probably should just start putting scale bars onto my pictures. I don’t have Photoshop, so I’d probably not do the semi-transparent grid thing.

  3. January 19, 2010

    There are free, online photo retouching sites that do many of the same things photoshop does. I did a quick search and found this one:


  4. January 20, 2010

    Hm, well, that looks interesting. Thanks!

  5. January 20, 2010

    Anything to help! You’ve inspired me to pursue my own intellectual passions more fully.

  6. Mark permalink
    January 30, 2010

    Elderberries have a stem that is not truly hollow, but filled with soft pith which presumably the beetles could easily chew a tunnel.

    There are at least two species of elderberries, though the taxonomy is confusing. As best I can tell, red-berried elderbery (S. racimosa or S. pubens) is circumboreal.

Comments are closed.