Andromorphic female Eastern Forktail

I found something cool when Stylurus and I were doing our weekly Odonata census at the Detroit River International Wildlife Refuge Humbug Marsh Unit. Although the final report will only classify relative abundance of each species into one of five simple classes, I have tried to actually count all the individuals we encounter on our transects and plots. This isn't too hard for most dragonflies, but quickly becomes tedious for damselflies. Obviously, it isn't possible or necessary to count every single one, but I tally what I see as I walk slowly along, and have to net a lot of bluets and forktails to make sure I'm getting the right ratio of similar species.

The other day a slightly odd forktail caught my eye. It resembled a male Eastern Forktail (Ischnura verticalis) with a bright green thorax and mostly black abdomen, but the tip of the abdomen had a very reduced blue pattern different from any species of forktail that I could recall. Netting it, I was surprised to see it was a female. I put it in an envelope to examine later.

At home I gave it a close look. It had a vulvar spine [1] and what I could "read" of the prothorax and mesostigmal plates [2] under my microscope indicated it was an Eastern Forktail. However,we'd never seen an illustration of one so strongly male-like and the bright blue pattern on the dorsal abdomen tip was unlike any we'd seen -- on any forktail.

Many species of damselfly have a female morph that is colored like a male. They are not only the minority morph in populations, but also very rarely seen. First, once they get older and more pruinose, they look just like typical females. And of course, not too many people look at enough inch-long insanely abundant insects in the grass to pick them out.

I solicited comments on my photos. Both Nick Donnelly and Dennis Paulson confirmed that this was a rare andromorphic female Eastern Forktail (Dennis has seen only one in his long career). In fact, the incidence of andromorphs in this species is under 1%. Here are the photos; all are clickable for larger sizes. More background follows.

It has been proposed that male-like morphs in female Odonata serve to protect females from being harassed by males. This theory was supported by the fact that female polymorphism occurs more often in species where males search for mates, versus families in which males are territorial (whereby females can avoid harassment by avoidance). The situation is actually somewhat more complicated than that -- beyond the scope of this post. A paper reviewing female andromorphs, various explanations, and evolutionary history is listed and linked to below. It cites a study (done in Michigan, coincidentally) giving the frequency of andromorphs in Eastern Forktails as 2% of 553 individuals and 0 out of 386 others. My specimen will be housed at the University of Michigan's Museum of Zoology Insect Collection.

As an aside, Russet-tipped Clubtails (Stylurus plagiatus) are increasing in number at the same site. A few very teneral individuals were found, along with a number of older ones, and a pair in tandem. Here's a cooperative male:

The evolution and frequency of female color morphs in Holarctic Odonata: why are male-like females typically the minority? (PDF). Ola M. Fincke, Reinhard Jödicke, Dennis R. Paulson and Thomas D. Schultz. 2005. International Journal of Odonatology: 183-212.

[1] Vulvar spine = point on the underside of the 8th abdominal segment in some damselflies; Eastern Forktails have one, Fragile Forktails (I. posita, the other common forktail in my area) do not.

[2] Prothorax and mesostigmal plates = structures behind the head of female Odonata that enable the male claspers to fit and lock on when the pair are in a mating wheel.

Best population of Great Blue Skimmers

Yesterday, I was doing some bird work in an undersurveyed area in Riverview, a downriver community of Wayne Co. Young Patriot's Park is a place I'd been a couple of times -- ball fields, a playground, library, basketball courts, and a woodlot at the northern end. The name stems from the period (1956-1962) when the site was a Nike missile base.

There is a decorative mowed-to-the-edge pond out front, and lots of skimmers and Pantalas flying around the open areas. I'd walked the edge of the woodlot for birds before, as well as some of the trails in it. Yesterday, I started at the north end, and soon discovered that there is a "creek" -- really a straight, shallow ditch -- running through the north end of the forested area. It's been extremely dry here, and the ditch was either dry, damp, or with perhaps three or four inches of water at its deepest. Kids had built a bridge across it where it crossed the trail, but there was plenty of naturally-fallen saplings as well as the usual discarded objects ubiquitous in urban waterways. Personally, I hopped across on a soggy car seat.

It wasn't too hard to walk close to the edge most of the way, as the woodlot clearly flooded in spring, especially on the north side of the ditch, so there wasn't as much undergrowth. The first thing I saw was a male Great Blue Skimmer lazily gliding after a conspecific, then perching in the dappled sunlight on a broken shrub arched across the water. If there is one thing about this species, it is certainly predictable in its habits.

Every few yards, in sunny spots, there was another one or two males. Standing in a patch of grape vines along the banks, two kept mixing it up and landing at my feet. Of course, I did not have my good camera, only a point-and-shoot. The fact that I finally got this nice shot (the best of any so far) and several others is an indication of how unwary and close they were. I didn't have a net either, but did try to swat one with my bird checklist.

They are not that unwary.

At one point I looked ahead, and saw a female skimmer ovipositing in the ditch with the same forward-flicking abdomen dip that I associate with Orthemis. She was very dull and in the shade, but when she finished and went up to a sunny leaf to perch, I saw it was a female Great Blue. The ditch only ran a couple of hundred yards, and without too much effort I was able to count around 15 males and at least 4 ovipositing females. These are the first females seen in the county, and the first positive evidence of a breeding population in the state.

Recap:

• We take the first voucher specimen for Michigan in Westland, Wayne Co., on 10 July 2005, ten years to the day after one was photographed at the same location. I just published a paper on this in the journal Great Lakes Entomologist.
  
• On 28 August 2005, we found several males in a wooded wetland adjacent to the Huron River at Willow Metropark, Wayne Co.
  
• On 16 June of this year, we found a male at a wooded wetland in Canton, Wayne Co. It was still there a week later, but no others were found and we haven't been back again.

This was just an odd and unlikely location, but it clearly floods a lot in spring, and probably stays fairly wet in less-parched summers. It will be worth a few return trips.

The blues

Last weekend when doing some bird survey work close to home in the urban jungle, Stylurus was surprised to find several Spatterdock Darners, Rhioaeschna mutata, in a small pond adjacent to the channelized portion of the Rouge River. This is a species we first had a glance at in 2005, and which eluded our nets at a retention pond in 2006 -- the first records for the county. Believe me, we know every wet spot in our city, and they've never been at this familiar pond.

It's locally referred to as "the oxbow pond," but in fact before the channel was built the river bowed in the other direction (the real oxbow ponds can be seen in the last photo below, to the left of the sewage plant), and this pond was either a natural wooded wet spot, or dug during construction.


It looks rather bucolic in the photo above. It's half-covered with spatterdock (Nuphar polysepalum), but one end and part of one side are being heavily invaded by phragmites. It's wooded around the rest of the perimeter. There are fish there (as a busy kingfisher demonstrated) which are probably larger and more numerous than past years, as the edges have become so thickly overgrown there is little access for folks who used to sneak in and fish there. The homeless folks have even abandoned their long-standing camp there.

Below, the red arrow points to the pond.

There's nothing sadder than a river in a concrete channel, in my opinion. This is the same stretch, just downstream of the pond. Ford world headquarters is the building in the distance on the right.

We returned yesterday, and Stylurus bravely made his way a few feet out from shore in the water at the only access point in the phragmites. I bravely tried to find access at the opposite shore, bushwhacking my way through sharp hawthornes, grape and poison ivy vines, and various discarded appliances. Along the margin, I was able to voucher one of a few Sedge Sprites, Nehalennia irene, a first for the city, and perhaps an indicator that the water quality is improving. Meanwhile, Stylurus was able to get the first voucher of the darner for the county.

This is the most beautiful of our darners, I think. This individual was bit battle-worn, missing half a leg and one foot. We did not observe any females, and the fish in the pond would prohibit much successful reproductive activity. So far, this has just been a terrific year for odonates -- nearly every species in abundance and in new places. To a great extent this likely reflects past conditions (up to two years ago) that allowed for greater dispersal of adults followed by increased survivorship of eggs and larvae.

We score!

In our long quest to voucher Anax longipes for Wayne County, we ended up the 2006 field season with a score of Comet Darner 4, Urban Dragon Hunters 0. Let's recap:

• 2004, seen at Sherwood Park, Sumpter Twp. several times, first county sight record.
• 2005, seen two different occasions at the Detroit River International Wildlife Refuge, Humbug Marsh Unit (DRIWR).
• 2005, seen in Northville Twp. in a retention pond.
• 2006, seen in Taylor, in another retention pond.

I was just awarded a grant to do baseline standardized odonata surveys at the DRIWR, as they will be restoring a large brownfield along the Detroit River shoreline, including opening up a creek that is currently underground, and constructing a pond. We did our first survey yesterday. About halfway through our sweaty second transect, a very large darner landed along the treeline. Both Stylurus and I were able to locate the perched insect: a big Anax, which looked like a female Common Green Darner (A. junius). We're just as prone to wishful thinking as the next person, but from our looks, neither of us could see the bullseye pattern on the forehead which would verify junius (right). Before we could contemplate how to get at this darner, it flew again.

It's hard to describe the sort of low-key desperation one feels when you know you might have just seen a really great dragonfly, one that you have to catch either to confirm its identity or voucher for a location, only to see it fly away. It might perch again right in front of you, or it might take off and go far, far way. This one did a few lazy loops, and landed in a locust sapling about three feet high, within a few yards of us. We crept forward, watching it with binoculars and looking for the bullseye. What we saw was... nothing. No bullseye = Comet Darner.

Although I carry the shorter net with the narrower mouth, I was a bit closer, directly behind her, and tend to be a little more of a patient stalker than Stylurus. My net bag has already been sewn up a few times, so ripping it on the locust thorns was a risk I was willing to take. Stylurus was ready off to the right. I swung, and made a clean catch without even tearing the net.

Extracting it from the net, we found out that indeed, we'd finally bagged our county voucher. This was a different location at the DRIWR than I'd seen Comet Darners previously. I suspect they occur here because the river acts as a corridor; there are no appropriate fishless ponds (or any other surface water) for them to breed in. But this bodes well for when ponds are built on the Refuge.

From the photo above, it's hard to get any true perspective on size, and she sure looks like a green darner (although the big, long reddish legs don't seem right for junius). We decided to snag a green darner just for comparison:

Longipes is much heavier bodied and just looks like a junius on steriods.

We resumed our survey, in which we ended up with 25 species. Sedge Sprite (Nehalennia irene) was a new species for the Refuge, for a total of 33 species since I first began doing bird work there several years ago.

We'll be doing biweekly surveys for the rest of the summer. Stay tuned.

Long time, no see

I realize this is a crappy photo, but it was beyond the range of the macro lens I had on my camera at the time. It's a Four-spotted Skimmer (or chaser, as you folks across the pond say), Libellula quadrimaculata. There are only three specimens from the county, all before 1917. Now there are four.

We found it, and one or more conspecifics, in a retention pond behind a Wal-Mart in Canton, a place we'd not been before. It was nearly entirely grown in with cattails, and mostly full of Twelve-spotted Skimmers (L. pulchella), along with a few pondhawks (Erythemis simplicicollis) and dashers (Pachydiplax longipennis) and lots of teneral Sympetrum. This was actually a birding stop for us, so I was without my net. When I saw this dull, hairy ode amongst the twelve-spots, I called for Stylurus to come around my side of the pond. By that time, the four-spot was landing repeatedly on this dead stalk. I wasn't expecting much new, nor did I realize four-spots were so furry and dull. It was a really nice unexpected surprise!

There was a little two-track heading back to the small woodlot near the pond. Since we were doing breeding bird atlas work, we thought we'd poke around. Not a hundred yards in, we found a small wooded wetland, easy to get to and quite open compared to similar ones we've found in the county. Even though it's been dry, there was plenty of water, and although our feet got wet, we didn't sink into deep stinking muck to get to the water's edge.

Stylurus immediately had a female Swamp Darner (Epiaeschna heros) ovipositing on a rotten log. I won't even display the horrible shots I got of that. My next thought was that the site looked like a great place for Great Blue Skimmer (Libellula vibrans), very similar to the site where we vouchered the first state record two years ago. I hadn't had time to voice that thought when I got a call on the radio from Stylurus, who'd wandered ahead and found a male GBS. I'll also pass on the crappy photos I took of that one, sitting over the water on a twig. This is our third location for the species in the county. Stylurus also thought he may have seen a female -- so far, we've only seen males.

It's always fun to find a new spot, although predictably this property was for sale. But it had no trails through the open understory, not many invasive plant species (and lots of less-common species for here, such as sassafras and tuliptree), and only minimal dumping or teenage presence. And to find a new species for us for the county, plus two other "good" odes made it a satisfying day.