Clubtails at the Sunrise Landing

[centuryplant]

Last week pameladean and I went to the Sunrise Landing on the St. Croix River to look for clubtail dragonflies. Many clubtail species are hard to find, in part because they're vulnerable to pollution, but all the public water accesses along the St. Croix have a good variety of species. We timed our visit to catch the emergence of two particularly elusive species, the Pygmy and St. Croix Snaketails, which we thought would be easier to find if we could find them before their wings dried. This was the second time we tried that, and the second time we failed; last year I think we went a little too late, and this year the river was too high to walk along the bank and look for them. I only saw one Snaketail the whole day -- a Rusty Snaketail, the most common kind, though not quite common enough to take for granted. I like their russet-and-pea-green color scheme and their wonderfully incatatory scientific name, Ophiogomphus rupinsulensis.

We did see a lot of clubtails in the genus Gomphus, which had probably emerged that day and were making their first flights into the woods. I've never seen so many at one time before -- everywhere you looked there was one. Most Gomphus clubtails are bright yellow and black when they're new, like this Midland Clubtail:

As they get older the yellow fades to silver in front, leaving yellow only on the swollen "club" at the end of the abdomen.

I'm going to have to get some help with the identification of this one, since there are several small species with inconspicuous clubs that look very similar. I'm hoping it will turn out to be a Green-Faced or Mustached Clubtail, since I haven't seen either before. Unfortunately, the best field mark for distinguishing them is the presence or absence of dark markings on their faces, and this one kept flying further into the woods as I tried to circle around for a better view. I suspect an expert will be able to tell what it is anyway.

This is a Skillet Clubtail that I photographed at the same landing in June 2008. Here the club is ridiculously huge -- larger than in any other Minnesota species, though the Cobra Clubtail comes close. Both species are favorites of mine, just because they're so improbable looking.

It's not clear what having a clubbed abdomen is good for. It's been suggested that it might improve maneuverability somehow, since some clubtails are incredibly acrobatic fliers, even as dragonflies go. Apparently no one has studied how they move their abdomens in flight, though. Clubs might also be an example of runaway sexual selection, like peacocks' tails. Looking at the Skillet Clubtail, that's easy to believe. But as far as I know nobody has tested that theory either.

Comments

[redbird]

I should at least go look in the local park (along the river with bit of salt marsh) on the weekend and see if we have dragonflies yet, since summer tends to be a little earlier here than in Minnesota. (A serious trip to marshland may not be in the cards right now.)

[centuryplant]

If you have salt marsh you might have Seaside Dragonlets.

[redbird]

Since what I have is in fact a tidal estuary, that seems likely.