Mating Soldier Beetles

2012 December 22

I spotted these two beetles mating on our big window on May 25, 2012.

They kept this up for a long time, allowing plenty of time for me to get the camera.

They didn’t move much, but if they did I’m sure that she would have just dragged him along to wherever it might be that she wanted to go.

This is not the first time this beetle species has been posted here; one of them appeared previously back in 2009. These were identified for me on Bugguide by v. belov as the species Cantharis rufa. This particular species seems to live most of the way around the Arctic Circle, being common in northern Europe and eastern Canada. They are probably another one of those cold-tolerant species that used the Bering Land Bridge to get here sometime around the close of the last ice age. They come out very early in the spring even in cold weather, and in previous attempts to photograph the species I found that putting them in the refrigerator barely slowed them down at all.

These are pretty much beneficial from our point of view, as soldier beetles are mostly carnivorous, and have carnivorous larvae that live in the leaf-litter. They therefore are useful pest-control in the garden. Given how visible and easy-to-catch they are, I expect that they are also foul-tasting like their relatives, the fireflies.

These beetles are very common every spring, and we are as likely to see them mating as not. The one in the previous posting had been found as part of a mating pair, too, but the previous pair disengaged and the male ran off when I disturbed them. Which is why I was careful not to touch them this time.

One might wonder why so many insects spend such a long time coupled together and mating. Sometimes it seems like they will stay linked up for hours. Which, given their small size, seems to be a lot longer than would be necessary for the sperm to travel maybe a millimeter or two. So, given that when they are linked together like that they will be a lot more vulnerable to predators, why do they take so long? The general opinion seems to be that the male is just trying to keep any other males from mating with her. As long as he is there, he can physically block any other males, and thereby ensure that all of her eggs are fertilized by him, and not by some other beetle. So, for him, the risk of getting both of them killed is worth the added likelihood of fathering a higher percentage of her offspring. Of course, from her point of view, she’d be better served if he finished up and got out of there, and stopped risking her life along with his. Which is just another case of what is good for one partner, isn’t necessarily good for the other. Although, in this case, if their primary defense against getting eaten is foul-tasting (and possibly toxic) “blood”, then she probably isn’t actually at much higher risk of getting eaten due to dragging him around.

3 Responses
  1. Phil Quenzi permalink
    December 23, 2012

    Hi Tim,
    Have you ever seen rabbits eating meat? I have numerous trail camera photos of snowshoe rabbits eating from a deer carcass I have out for the birds. I will look at the carcass closer to see if I can tell if they are eating the meat or knawing on the bones.

    Merry Christmas

  2. December 30, 2012

    “One might wonder why so many insects spend such a long time coupled together and mating.”

    Maybe it just feels good. Life is a kludge. It doesn’t always make logical sense.

  3. January 3, 2013

    Phil: No, I haven’t, although I did read about it a long time ago (in a kid’s nature story, of all places). It sounds like some cool pictures. Sandy says that she thinks that a lot of “herbivores” aren’t nearly as herbivorous as people think.

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