Dragonfly Monitoring Update

by Carl Strang

Earlier I described  my first venture into dragonfly and damselfly monitoring by kayak. I have been out on the Des Plaines River twice since then. There has been some variation in the count of species and individuals each time, but most seems unremarkable. I’ll focus on a couple high points. The biggest surprise was a transition in the damselflies. The slender bluet was the common black type bluet my first time around.

Slender bluet 5JL 1b

Bluets are a group of small to medium sized damselflies. Black type bluets are so called because their abdomens are nearly all black as viewed from above. On my second and third outings, the slender bluets were replaced by stream bluets as the common black type bluets. Here is one of the latter I rescued from the water.

Stream bluet 23JL09 1b

Note that, in contrast to the slender bluet in the top photo, the stream bluet has a slender blue shoulder stripe with a wider black stripe below it. “Eye spots” on the back of the head are smaller in the stream bluet, and there is less blue in the abdomen tip. Stream bluets were largely in tandem pairs and actively laying eggs on floating vegetation during both recent outings.

Stream bluets tandem b

The other surprise is the relatively large number of orange bluets. Here is one sharing a photo with a stream bluet.

Orange and stream bluet b

I’m not saying that the river is swarming with them, but in my experience a count of 13 orange bluets in a 2-hour outing is a lot. A final note is that eastern amberwings have become the most abundant dragonflies, despite my seeing none on the first outing. Here is a photo of one from 2007.

Eastern amberwing male 2b

I have decided to limit my monitoring to the stretch of river that bounds Waterfall Glen Forest Preserve. This gives me a span of stream between the launch ramp and the preserve in which I can practice another type of inquiry, to be featured tomorrow.

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