Saturday, November 19, 2011

The Spotted Spreadwing (Lestes congener): A Quick Look

 
A reader recently requested that I write a post on the spreadwings (Lestes) in the region—something I had been thinking about for a while, but I haven’t been able to sit down at the blog machine much lately. So for now, I’ll just present a few words and images of one of the more common Northwest Lestes, and the one which is most expected during the tail end of the season in this region (and I think over much of its range, which is a significant portion of the United States and southern Canada).

Male Spotted Spreadwing, Lestes congener
(close-ups of the photo at top): the head and
thorax above, the end of the abdomen below.
The Spotted Spreadwing (Lestes congener) is fairly distinctive among the Northwest species: its thorax is mostly slaty gray over the dorsal areas with minimal, if any, metallic colored reflections, and largely lacking obvious pruinescence; the pale antehumeral (“shoulder”) stripe is very thin and light brown in color—never pale blue or greenish-blue; the pale pruinescence at the tip of the abdomen is limited mostly to the last two segments—S9 and S10, with just a thin, partial coating dorsally on S8.

There is often times a very thin pale median stripe on the thorax too, but not always. There are one or two dark elongated spots—what this species is named for, low on each side of the thorax, and often visible from a lateral view (see the female below). Other species, at least sometimes, have these too, so don’t assume you’re looking at this species if you see spots.

If you can see them, the males’ paraprocts (lower abdominal appendages) are short—about half the length of the longer curved cerci (upper abdominal appendages). The Archilestes (California and Great Spreadwings) have short paraprocts too, but they are noticeably bigger species with unique thoracic patterns. Our other Lestes, however, all have longer paraprocts. As always, I encourage in-hand examination if you want to make sure.

Female Spotted Spreadwings are very similar to males in overall pattern and coloration, but have little pruinescence, especially on the abdomen. Their eyes are always brown unlike the females of our other species which are sometimes, at least, blue (the females of some species are polychromatic with either blue or brown eyes at maturity). The ovipositor is relatively short, but this can be difficult to judge without experience or comparison to other species. Some other species have short ovipositors too.

Female Spotted Spreadwing, Lestes congener.
 
The species most similar to Spotted Spreadwing in this region is the Black Spreadwing (Lestes stultus—possibly a subspecies of Emerald Spreadwing, L. dryas, but currently considered a valid species), although it is largely restricted to lower elevation and foothill areas of Northern California and southwest Oregon. It also has an earlier flight season (with some overlap).

The Black Spreadwing has a more robust build—females especially, and quite often has more obvious colored metallic green, purple, or bronze reflections on the thorax (sometimes abdomen too). The males’ paraprocts are longer with angled tips that are vaguely foot-shaped; the female’s ovipositor is a bit longer and more hefty.

Another difference is that male Black Spreadwings often, but not always, have more extensive pruinescence at the end of the abdomen, extending more noticeably onto S8. I’ve also noticed a little difference in the shape of the pale antehumeral (“shoulder”) stripe—at least on males: on Spotted it tends to be a little constricted before a more bulbous tip at the posterior end; on Black it is more evenly tapered. This is a subtle difference and subject to variation (like all characteristics). Again, I encourage in-hand examination of the structural differences if you want to be certain.

So look for the late-flying Spotted Spreadwing if you still have some decent weather in your area—I’m thinking the warmer parts of Northern California at this date. I don’t expect to see anything in my neck of the woods until next spring, but it will be much longer until the Spotted Spreadwings are out again!

5 comments:

  1. Thank-you for humoring me with the Lestes lesson I requested. I mostly see black spreadwings where I go, but I suspect I've had spotteds mixed in. I must swing my net some more so I can be sure!! It will have to wait until next season as most Odes are gone for now- even here in N.California. I suspect this last round of rain and snow down to 1500' will likely end most of what was left of the ode activity.

    ReplyDelete
  2. I have yet to collect a spreadwing here in the Ozarks, but I've only been looking for odes for two years. Am I correct that they are usually found in streams, as opposed to ponds?

    Most of my collecting is in clear, fast Ozark streams, but I get the impression they might prefer somewhat slower-flowing streams. Is this right?

    Looks like the only species found so far in my IMMEDIATE area are Archilestes grandis, Lestes australis, L. congener, L. eurinus and maybe L. vigilax. Would really be cool to find some next year.

    ReplyDelete
  3. @Sandra H. Hi, Sandra. You're welcome, and thanks for the suggestion. Eventually, I do a post comparing all of the Lestes, but it might have to wait a bit. Keep in mind that Black Spreadwing is an early species and Spotted is a late species. There is some overlap, but I don't think a great deal.

    ReplyDelete
  4. @George Sims Hi George. Actually, the Lestes are mostly pond/marsh species, not stream species. Maybe that kind of habitat is not common in the Ozarks, but there must some places with standing water and emergent vegetation. Some species specialize in seasonal wetlands-- around here dryas and unguiculatus are like that.

    ReplyDelete
  5. I'm just beginning to "diversify" a bit, but it's been difficult, 'cause these streams here are so GREAT, clear, and beautiful. I am mucking about in a few ponds now, mostly grabbing Enallagma thus far. Those mucky pond bottoms remind me of why I left Louisiana.

    ReplyDelete