Taking to the water

Part of a grant I received to do baseline odonata survey on USFWS land included larval sampling. It's still a little early in the fall (we discovered) to get a lot of semi-mature (and therefore identifiable to those of us who specialize in adults) larvae. But we decided to spend a glorious autumn day seeing how it would go.

We sampled several areas. One was a portion of the Detroit River. Stylurus is a champ: he waded right in. That's the north end of Humbug Island in the background, and Grosse Ille in the far left background. This is near the southern end of the river. The substrate here is alternately sandy and silty, with the remains of wooden planking installed by a private hunt club decades ago still sunken in the muck in a few places. That's (mostly) duckweed on the river, not algae.

A main objective was to see what is able to breed in an Army Corp of Engineers ditch, created to shunt an old creek, currently nearly entirely underground in a sewer pipe, to the Detroit River. Although mucky and peppered with trash, this little shallow creek has small fish, several kinds of gastropods, freshwater scuds, water boatmen, many aquatic beetles, and some odonate larvae. Aside from a variety of damselfly larvae, we got about a dozen larger specimens of darners and skimmers. Still, not as many or as diverse as we would have hoped. However, this creek is slated for restoration, hence our baseline survey. Here, a friend we enlisted to slog through the mud checks out his haul.

I stayed relatively dry, sorting through the trays of gungus that the men brought me. Note to self: bring a folding table and chair next time. Kneeling on the ground hunched over the trays was bullshit. At least I remembered my reading glasses.

Once finished, we couldn't resist tromping around one of the areas where we typically do transects counting adults. We both saw a nice gomphid -- Arrow Clubtail, Stylurus spiniceps or Elusive Clubtail, S. notatus -- but were unable to net it to confirm its identity. There were a lot of Wandering Gliders (Pantala flavescens), some Common Green Darners, Anax junius and Black Saddlebags, Tramea lacerata, a few Common/Eastern Pondhawks, Erythemis simplicollis, and lots of bluets, mostly Familiar (Enallagma civile) or Tule (E. carunculatum) with a few Orange (E. signatum). And the typical Aeshnas for the date and place: A. umbrosa, Shadow Darner, and A. constricta, Lance-tipped Darner.

The next installment might just be about what we found, once we key out our three dozen or so specimens.

Great Spreadwings persist

Nearly two years ago, Nannothemis and I found the first state record of Great Spreadwing (Archilestes grandis) for Michigan in northwestern Wayne County. Last year I was delinquent in checking the location in late summer/early fall. One reason for not visiting was my fear of seeing the area around the stream fully developed with office buildings and restaurants and the watercourse being destroyed by trash and runoff. As is too common in southeast Michigan, land is being gobbled up and developed for office parks, restaurants, and shopping areas. This photo from Google Maps shows the vacant land; the creek is visible snaking through the property.


The area is now completely built out; here is the site plan:

On 29 August, while running an errand during lunchtime, I decided to check the stream and development "progress". I was surprised at the amount of vegetation left intact along portions of the stream. Also, there wasn't a large amount of trash or debris in the stream, which was encouraging.
Immediately I found a male Great Spreadwing and subsequently found 2 other males and a female along ~100m of the stream. I only had 10 minutes to check the area and I would guess there were more individuals present. This is a record early date for Michigan by nearly one month.

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.