Darkling Beetle

2007 December 29

When I found this beetle crawling across the floor in the basement, I knew what it was right away:


It’s a darkling beetle, Tenebrio molitor.


The reason I know what it is right away: a couple of years ago, S_ was raising them to use the larvae for fishing bait (and, of course, for amusement value)[1]. The larvae are better known as “mealworms”[2], and are actually sold commercially as food for lizards, snakes, birds, and other pets that like to eat live insects. They are also well-thought-of as bait for panfish, particularly for ice fishing.

This is a cosmopolitan species that has either been taken all around the world by humans, or managed to get pretty much everywhere on their own simply by being adaptable and mobile. They really aren’t that much of a pest in the house, they are much worse in granaries where there is damp grain for them to eat – if you keep things dry in the house, the larvae just don’t do well, and they need to eat quite a lot, so it takes a noticeable pile of food to really breed them.

They are pretty much your classic beetle, with all the beetle parts, including the oh-so-typical claws on the ends of their feet, which let them crawl all over a wide variety of surfaces:


It’s actually fantastically easy to raise these, and they are pretty amusing to watch transform from grubs to beetles. You can get rearing kits and food from lots of different places, but I like Ward’s Natural Science, who have a pretty reasonable price and who also have lots of other interesting things for sale[3].

[1] The amusement value lasted right up until the dogs decided they looked tasty, and knocked the container off of the countertop to eat them. Of course, the dogs didn’t get all of the worms, and pretty much ignored the adults, so it made quite a mess and we were finding the beetles scattered about for days afterwards. It is quite possible that this one is a descendant of that original population.

[2] When I was a kid and first heard references to “mealworms” as food for lizards and similar pets, I thought that they were called that because they were nice to make a meal off of[4]. It turns out it is because they infest meal (as in, ground
grain products)

[3] Ward’s originally started as dealers in mineral specimens, specializing in meteors, but they have really branched out over the many years they’ve been around. Fossils, live specimens, silkworms, laboratory apparatus, microscopes, you name it. They mainly sell to school science labs, and in the old days it was hard to get their catalog unless you were affiliated with a school. But, in these heady internet days, they’ve got their catalog online and are more than happy to sell to anybody.

[4] I’m not 100% certain, but the “Gagh” that the Klingons ate on Star Trek looked a lot like mealworms to me, although they
might have been the giant mealworms, Zophobas morio, which are way bigger than regular mealworms.

7 Responses
  1. December 31, 2007

    So that’s the grown-up version of those little grubs that my pet chameleon used to eat. Fascinating how they change so drastically.

  2. December 31, 2007

    …Cool claw photos, too!

  3. Sandy (the wife) permalink
    January 5, 2008

    Tim writes in this entry that I was raising these cuties as fishing bait and that they are commonly used for ice fishing. Actually, when he says I was raising them, “for amusement value, also,” that was the whole reason I was raising them. Just for yuks. What I use for ice fishing is wax worms, which are completely soft and succulent and well liked by pan fish. Meal worms are kind of hard and unappetizing (although I haven’t tried eating them, yet, unlike wax worms). There may be places where people fish with meal worms, but around here all you find for sale in the winter at bait shops is wax worms.

  4. Sandy (the wife) permalink
    January 5, 2008

    Alright, a short update. I went looking for pictures of wax worms online to add to my post and I found this incredible site. Neon colored wax worms. I’m taking it as a personal challenge. I’m going to figure out how to make my own. Better chemistry meets better fishing, my heart is all atwitter.

  5. brandon permalink
    March 17, 2008


  6. Emily permalink
    March 1, 2009

    nasty!!! but i have the same thing in a bottle because of a science project.

  7. August 27, 2011

    i have to do this for a project and ether u get to draw it take pictures or catch them but im drawing 🙂

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