Predatory beetles

As I was taking an early evening walk around the garden yesterday, a sudden flurry of movement drew my eye down to the mulch.  I poked around and uncovered a beautifully camouflaged little insect.  It was a rove beetle, probably Platydracus maculosus, the first I have seen in the garden.

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rove beetle (Platydracus maculosus?)

Rove beetles are predatory beetles with a very unbeetle-like appearance.  They have short elytra (wing cases) which leave the abdomen exposed.  Some species (there are about 63,000 species total) will curve the long abdomen when threatened, giving the appearance of a scorpion.

While Platydracus maculosus may be beautifully camouflaged, it isn’t the most beautiful predatory beetle that I have seen in my garden.  That accolade belongs to Calosoma scrutator, the fiery searcher.

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fiery searcher (Calosoma scrutator)

C. scrutator is one of the largest ground beetles in North America, and its alternative common name, caterpillar hunter, tells you all you need to know about its preferred prey.

fiery_searcher2

Smaller and more common than C. scrutator, but equally fierce, is Cicindela sexguttata, the six-spotted tiger beetle.

Tiger_beetle
six-spotted tiger beetle (Cicindela sexguttata)

I often see these little beetles patrolling sunny paths in the garden or our concrete driveway.  When approached, they usually fly a short distance, looking rather like a shiny green wasp, before landing and running rapidly away.  As a child, I learned the hard way that tiger beetles can bite hard.  If you must catch one to show your friends, put it in a jar.  Don’t hold it cupped in your hand.

The strangest of our resident predatory beetles, stranger even than a rove beetle, is the railroad worm (Phengodes species).  Males have large, feathery antennae and wings that extend beyond the elytra, making them look a bit like a fly or a moth, but it is the females, also called glow-worms, that are really weird.  The females are larviform (looking like a large larva) and have an elongated, segmented body lacking wings.  Each segment has a pair of bioluminescent spots, so in the dark the railroad worm resembles a train with glowing windows.

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female railroad worm (Phengodes species)

Railroad worms specialize in preying on millipedes, which they superficially resemble, and when disturbed they roll up, just like a millipede.

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Keep your eyes open.  Every time you go into a garden, there’s a chance you’ll see something you have never seen before.

7 thoughts on “Predatory beetles

  1. I had no idea, nor would have guessed, there are some 63,000 species of rove beetle. The one that is common here in the PNW is all black, not too large. It hides by day under any loose, moist cover. I’ve seen some epic battles between rove beetles and earthworms. The beetle usually wins, even if the earthworm is much larger. I hope they eat slugs.

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    1. I had no idea either, but who am I to doubt Wikipedia. Apparently rove beetles are the largest family of organisms.

      I wonder if your black rove beetle is a native or Ocypus olens (devil’s coach horse) which has been introduced from Europe.

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    1. Very cool. I don’t think I have ever seen a male, but they must be around. I’ve found four or five different females, including one in the house.

      Did your friend catch it at a light trap?

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  2. Fascinating . . . and some great photos. I often wonder if “nature” has a standard chemical process for bioluminescent spots – does the railroad worm have anything in common with glow-worms – another beetle?

    Liked by 1 person

    1. European glow worms and fireflies are closely related, so they probably have similar luciferase (generic term for enzyme that produces luminescence). I’m not sure if it is different than railroad worm luciferase.

      There are a wide range of luminescent animals and microorganisms which use different luciferases. Railroad worms are the only creatures that can produce red luminescence, though they also produce green luminescence like fireflies..

      I was able to see the luminescence of one railroad worm I caught but couldn’t get a good photo. Maybe next time.

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