Tuesday, January 14, 2014

Close Encounters with Dragonflies in mid-January

The New Year started off with some serious winter weather, but Mother Nature has given us a break for the past three days, with the temperatures hovering around a more bearable 5°C, plus or minus a degree or two. As good a time as any to take advantage of the moderate meteorologic conditions and search for whatever dragonflies might be out and about.

The woodland stream depicted in the next photos is along the trans-Canada Trail, roughly half a kilometer east of Tweed. This is the view looking north of the trail.

And it didn't take long to find a dragonfly. She is 30 mm in length, and it definitely is a girl – the tiny ovipositor can be seen peeking out between abdominal segments eight and nine.

A photo of the stream to the south of the trail, and again, a few scoops of sand and silt from the stream bed produced a pair young males. The larger of the two is 25 mm long, the other little guy is 18 mm in length.

This is the same site where I found the Spiketail naiads last August, and I know there are lots of them lurking in the bottom of the stream. The real purpose of this excursion was not to look for dragonfly naiads, it was to satisfy my curiosity as to what they might be eating. Are any of these insect species food for Cordulegaster larvae? I don't know for certain, but given what I've read about odonate larvae in general, they are voracious eaters and will take whatever they can capture and overpower.

There are some mayfly naiads inhabiting the stream but they are not common. Caddisflies are a bit better represented, I found two species, a small one that makes its protective casing out of grains of sand, and the larva in the following photo. (Incidentally, the insect was pulled from its case by accident, I didn't tear it out for the sake of a few pictures.)

I think the caddisfly larva is probaly genus Triaenodes, at any rate both the insect and its casing strongly resemble the one in the next photos (taken during the much warmer days of a summer long past).

There were also some stonefly naiads hiding in the leaf debris along the steam's edge. Like the mayflies, they are not common, and they are tiny, almost translucent, only about 5 mm long. Not much of a meal for the naiads that I dredged up, but good enough to feed a hatchling.

The most likely source of nourishment for the growing young Spiketails are the large, maggot-like critters in the following images. Based on their aforesaid "maggot-like" aspect, I surmised (as it turned out, correctly) that they might be cranefly larvae, indeed, I think they are the larvae of the Giant Crane Fly (Tipula abdominalis). The stream bed is teeming with these detritivores and one scoop of muck can yield half a dozen. They are large, normally chunky, oval shaped and grub-like in appearance and about 25 mm long, but can extend themselves to 40 mm or 60 mm.

The insects didn't like being out of their element and weren't co-operating, so this is best macro I could obtain of the spiracular lobes. Here's a link to some much better images at BugGuide.Net.

This is an old photo from a few years ago of the adult fly, not an uncommon species, and aptly named too.

The air was warm enough to permit some active insect life outside the insulating confines of the water and there were a few small black midges flying around. And before I left for home I saw this on the snow ...

A little Long-jawed Orbweaver spiderling, no longer than 3 mm. No matter how tough the circumstances or adverse the conditions, life goes on ...