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Monday, May 6, 2013

Tigers on the sand

When I left Massachusetts, I had been casually working on photographing all of the tiger beetle species in New England.  It was a great side project, especially because tiger beetles are attractive, fun to watch, and live in habitats that are interesting to explore.  I've had my eyes open for them since moving to California, but haven't encountered too many yet.

Last fall Eric spotted an iridescent green species along the Mendocino coast, but I wasn't there at that time, and was sad to have missed it.  This past weekend we looked again and were lucky to find a few individuals.

This was an open sand area along a coastal bluff.  The sand was very coarse, as you'll be able to see in the pictures.

The beetles were a dazzling bright green with cream-colored markings on their elytra (wing covers).  They were ~12 mm long.

The shape of the middle marking  the one that looks like a musical note — is very important for identification.  In fact, this beetle had me fooled at first before the shape of this marking clinched the identification as a Western Tiger Beetle (Cicindela oregona).

Note that the middle marking makes a very clear 90° turn starting from the margin, it runs perpendicular towards the center line and then drops straight down towards the tail end.  In a very similar species (Dispirited Tiger Beetle, Cicindela depressula), there wouldn't be such a clear 90° turn; instead it would be a more gradual, sinuous wave.

What had me fooled initially was the overall color.  I had seen Western Tiger Beetles before (on Bodega Head and in Oregon), but both times they were dark brown rather than iridescent green!

Here's another individual from the Mendocino coast.  The wing markings are slightly different, but you can still see the strong angle in the middle marking.

You might be wondering why they're called tiger beetles.  These are very active predators.  They use their long legs to sprint after smaller insect prey.  And they have very long, serrated mandibles to capture them.

Modified from A Field Guide to the Tiger Beetles of the United States and Canada (Pearson, Knisley, and Kazilek 2006)

I didn't get great photos of their mandibles this past weekend, but if you look closely you might be able to make them out in the photos below.  In the first photo the beetle is holding its mandibles open, while in the second photo they're being held closed and so the tips are crossed.

If you're curious, I posted a photo of a Western Tiger Beetle from Bodega Head last September.  Now I'm wondering about what drives the color variation in this species, i.e., why are some of them brown and others green?

1 comment:

Anonymous said...

There's actually something called a "Dispirited" tiger beetle? That is truly one of the greatest insect names, but makes me wonder what happens if the beetle cheers up? Identity crisis?