centuryplant | Color changes in dragonflies and damselflies (Reply)

Last July I took a drive through McLeod and Meeker counties, just west of the Twin Cities metro area, to look for dragonflies and damselflies. I chose the route after finding out from the Odonatacentral website that these counties' species lists were almost empty -- eight dragonfly records between them, and no damselflies at all. That's not so unusual for Minnesota. It's hard to understand: this state has tons of fresh water for odonates to breed in, and it should be an interesting place to study them because it's a crossroads -- lots of species' western, eastern, southern, or northern borders pass somewhere through the state. Yet for some reason we're way behind on filling out our county lists. On the range maps for some damselfly species, Minnesota looks like a hole -- as if they heard a bridge fell down and they're afraid to come here. So sometimes, instead of hiking in areas that are relatively well-studied, I drive around and look for new species in counties where, apparently, nobody has been paying much attention. There aren't always parks, but there are boat docks everywhere.

My last stop of the day was the Marion Lake Shorefishing Area, which is really nothing more than a few benches. The lake at that point has a steep shore with a lot of riprap to stabilize it, and above that is a wide mowed path, then another slope with tall grass going up to the highway. This is a good place to be at the end of the day because there aren't any trees nearby to shade it out, and you have light right up until the sun sets across the lake. Even so, it was getting pretty dim by the time I made it there, and most of the damselflies I found were perching on flowers and grass seedheads that blew around wildly in the wind. I wasn't sure any of the pictures I'd taken would be usable at all. I was happy to get home and find this:

I think those are aphids clustered upside-down on the stem. The large insect is a bluet, a very common kind of damselfly throughout the U.S. Most species are sky-blue and black, in a banded pattern that always reminds me of resistors. These are the sparrows of damselflies -- there are a lot of species that are very hard to tell apart. Most females can only be identified with a microscope. Males are a little easier: if you look at their abdomens from above, some of them are mostly black, and those species can, in theory, be identified through binoculars. Others are mostly blue, and can only be identified by examining the cerci at the end of the abdomen. This one is just about half-and-half on the middle segments, which means it's probably a Tule Bluet.

But what really interests me about this damselfly is that the blue bits aren't all blue. Young adult bluets are brown -- usually a pale brown with a drop of purple in it; the warmer tone here is probably produced by the sunset light. This one is just getting his adult coloration, and it's coming in in patches. I think it looks like turquoise in matrix -- as if the brown is being gradually polished away.

This is, I think, a Cherry-Faced Meadowhawk. As a young adult he was golden yellow, and when he reaches breeding age he'll be bright red -- the same color change that female dragons undergo in Jo Walton's Tooth and Claw, come to think of it. This one is just starting to change: you can see a spot of red at the base of the abdomen, as if somebody touched him there with a paintbrush.

This Autumn Meadowhawk is about half or two-thirds changed. The abdomen is red on top, with just a few small yellow spots remaining, but the thorax is just starting to blush. Notice the W. C. Fields nose, too.

Here's what Autumn Meadowhawks look like when they're completely red.

Chalk-Fronted Corporals start out orange-brown with a black stripe down the middle, but like a lot of skimmer dragonflies, as they get older they develop pruinescence -- white, gray, or blue stuff that sits on top of the cuticle and covers up whatever colors are underneath. Here the pruinescence is working its way down the abdomen.

Pruinescence comes from a word meaning hoarfrost, which is what it looks like when it's thick. When it's lighter, like on this one's abdomen, it always makes me think of the bloom on a grape.

Since pruinescence is on the surface, it can get worn away in older dragonflies, like this male Twelve-Spotted Skimmer. You can only see one side here, but there are brown patches on both sides of the abdomen, just where a female's legs would grip during mating.

This Eastern Pondhawk is demonstrating how dragonfly jaws work by swallowing a biting fly. He's also showing how a pale blue pruinescence replaces green in adult males of his species. Again this reminds me of turquoise -- a polished nugget with some color variation in it. His face shows the original pea green color.