Wednesday, August 20, 2014

Difficult to distinguish Darners

Yes, even after seven years of "dragonhunting" there are some species that prove to be my nemesis (or should that be nemeses?) when it comes to separating them in the field, namely, the females of Black-tipped and Lance-tipped Darners.

Male dragonflies are never a problem, they are easily distinguished by their terminalia, such as, for example, this male Black-tipped Darner (Aeshna tuberculifera). The inset shows the claspers and the "black-tip" – the all black S10, although in some individuals this segment may bear tiny blue spots.

The female Black-tipped Darner (Aeshna tuberculifera) is very similar to the male in terms of color and patterning. So far so good ...

Lance-tipped Darner (Aeshna constricta), male ... the inset illustrates the "lance-tipped" cerci, also note the blue spots on the upper surface of S10.

Now let's look at a couple of Lance-tipped Darner (Aeshna constricta) blue form females – as noted in field guides the styli are long and quite visible, but the styli of the Black-tipped Darner are noticeable as well, and lengths can be difficult to judge in the field. Unlike the male's last abdominal segment, the female Lance-tipped Darner's S10 doesn't bear any blue spots, so that doesn't help.

With a length of 71 mm to 78 mm the Black-tipped Darner is theoretically larger than the Lance-tipped Darner, which weighs in at 65 mm to 72 mm. But length is also tough to guesstimate in the great outdoors, and who bothers to cart a ruler around with them on a nature hike?

Lance-tipped Darner female #1

Lance-tipped Darner female #2

The following study of the differences between the females of these two species is based both on the material found in field guides and my own observations. Markings can vary according to the individual insect and by region so I'm not sure how reliable my observations are in the context of the big picture, but they work for me.

Lance-tipped Darner (Aeshna constricta), female:
– The lateral thoracic stripes are relatively narrow and notched.
– The dark lines separating the lateral blue abdominal spots are very straight and quite narrow.
– The blue line on S2 is continuous, and there is generally more blue than dark in this area.
The last two factors conspire to give the Lance-tipped Darner's abdomen a bluer overall aspect than the abdomen of the Black-tipped Darner.

Comparing the female Black-tipped Darner (Aeshna tuberculifera):
– The lateral thoracic stripes are broad and pale, sometimes almost white, and when the dragonfly is perched in a shady place they almost seem to glow.
– The dark lines separating the lateral blue abdominal spots are somewhat irregular, and larger than in the Lance-tipped Darner.
– The blue line on S2 is broken, there is more dark than blue on this part of the dragonfly.
– The face usually bears a thin brown cross-stripe.

Although not common, green and yellow form females occur more frequently among Lance-tipped Darners than Black-tipped Darners. There were a total of about fifty of these striking insects foraging high in the air and perching on the shrubs and this was the only green female encountered.

Note that although the colors are different in the next two examples, the patterning is still consistent with the blue form Lance-tipped Darner females studied above.

Two yellow form females were flying but I was only able to capture one of them.

Before sending this beauty on her way I had to capture an image of those awesome eyes ...

A green form female Lance-tipped Darner in a more natural pose, hiding in plain sight despite its size and eye-catching markings. The complex patterning breaks up the dragonfly's profile and makes it difficult to espy when it's perching among the tangle of background vegetation.

Christmas in mid-August

And why not Christmas in August? In my opinion any day a person discovers a cool plant or animal new to them feels like Christmas.

On this particular day I was searching for odonate naiads in a a sand-bottomed woodland stream near the intersection of the trans-Canada Trail and Sulphide Road (44.494167°, -77.285556°). I happened to look up, and growing on a shaded rocky bank covered with thin soil was a luxuriant patch of (what else?) Polystichum acrostichoides, better known as Christmas Fern.

A lower and upper surfaces of a fertile frond – only the pinnae toward the tip produce spores. The two lowest pinnae are angled downward.

A closer look at the dense clusters of sori.

The pinnae (note the bristly margins) have upward pointing lobes near their bases, think of the toe on a Christmas stocking.

The stipe and rachis are scaly.

The dark green glossy leaves – both the sterile fronds and non-reproductive parts of the fertile fronds – persist throughout the winter, always a welcome break from the monotonous white of a winter's day. Although there are other fern species with evergreen fronds, for whatever reason this one earned the name Christmas Fern.

Tuesday, August 12, 2014

A Forcipate Emerald at the Stoco Fen

Reputed to be rare and local, perhaps the Forcipate Emerald is more common than generally thought and is merely secretive, with a preference for habitats that are inaccessible to the average person, such as bogs and alder swamps – or the Stoco Fen.

Somatochlora forcipata is a medium sized dragonfly with a length of 45 mm to 50 mm. It flies from early June until mid-August and this male, encountered on August 11th, is beginning to show its age and its few yellow markings are obscured.

One thing time doesn't fade in an Emerald are its eyes. In fact, they start out life as rather dull orbs, and acquire the luminous green that seems to glow with an inner light only with increasing maturity.

The abdomen is relatively slender.

Many Somatochlora spp – especially older dragonflies with dulled colors – resemble one another closely even when perching and have to be identified in the hand. Even so care must be taken because the terminalia of the Forcipate, Incurvate, Kennedy's and Delicate Emeralds look superficially similar to one another. Here's series of images making a 180° "walk-around" the claspers.

A few other unidentified Emeralds (including a possible Brush-tipped Emerald)and Darners were sighted at the fen, and it is currently host to a robust community of Band-winged Meadowhawks (Sympetrum semicinctum). Who knows what other odonate surprises might be lurking out there in this unique little corner of the world?

Friday, August 1, 2014

Eastern Least Clubtail (Stylogomphus albistylus)

Yesterday while counting dragonflies and damselflies along the shoreline of the Moira River, south of the dam, I spied an odonate the size of a Powdered Dancer – about 40 mm long – come in for a landing. Much to my surprise the "Powdered Dancer" proved to be a tiny Gomphid. It was extremely wary and flew off when I approached it to take a picture, and the following photo, a far cry from being the acme of digital art, was all I managed to get. I sighted the little dragonfly a few minutes later but again couldn't get close enough for a decent photo or a really good look at its markings.

I was fairly certain my mystery dragonfly was a female Eastern Least Clubtail and one of the experts at Ont-Odes was of the same opinion. I resolved, weather permitting, to return the following day armed with a net and binoculars and see if I could acquire better evidence toward a positive ID.

Not long after arriving I spotted one of the diminutive dragonflies perching on some rocks not far from the shoreline. The pale terminalia clearly contrasted with the dark background of the water, and I think this may have been a male (I doubt if the tiny nubs that constitute a female's cerci would have been visible looking through the binoculars). However, I couldn't really tell for certain if I was looking at claspers and when I approached with the net the insect took flight.

After another half an hour of patiently waiting a female landed right at the spot of yesterday's encounter (no doubt the same individual). She wasn't quite so alert today and I managed to capture her. She's on the older side, past middle age, and although not seriously worn her wings show a little bit of fraying at the edges. The dragonfly's length is 40 mm dead on (I used a straw on site and measured it at home later).

The Eastern Least Clubtail (Stylogomphus albistylus) is gracile dragonfly, and the tip of the abdomen is not prominently clubbed, even less so in females than males. The abdominal segments are boldly ringed with greenish-yellow.

A look at the beautiful – almost luminous – green eyes and prominent markings on upper surface of the thorax.

A mug shot – don't mistake that "grin" for a smile, she was not a happy camper and constantly kept trying to bite me.

Although the female's cerci are nothing like the intricately sculpted structures of the male, the terminalia are pale – almost white – in both sexes.

After the photo session the little lady was free to go her way in peace, or whatever little peace there may be in the odonate world. There was a Black-shouldered Spinyleg perching on the rocks in the same area, and though none were about today there are usually a few Dragonhunters patrolling the river. Both species are fast, powerful fliers and should one of these much larger clubtail cousins espy the Eastern Least Clubtail there's no doubt as to the outcome ...

So many things come down to nothing more than luck. Considering this dragonfly's habit of perching on emergent rocks in the middle of the river it's no wonder I've overlooked it despite surveying this spot fairly thoroughly for several years, and had it not been for yesterday's chance encounter I would still be ignorant of this gem's presence so close to home, practically in my back yard.

The barren, rocky river shoreline at the Vanderwater Conservation Area seemed like another promising place to search for the Eastern Least Clubtail, as the odonate species there are much the same as closer to home. On June 15th friend and I visited a location (44.38019°, -77.31537°) where in addition to the aforementioned shoreline there is also a forest, a woodland stream and a seep along the side of the road, and a dry meadow, all within tens of meters of one another, making for an interesting juxtaposition of habitats. And at a bridge not far from the Vanderwater Conservation Area (44.421932°, -77.306281°) he encountered and photographed a Rusty Snaketail (Ophiogomphus rupinsulensis).

August 08 was warm and sunny, it seemed like a perfect day to check out the Vanderwater Conservation Area and – jackpot! – at about 2:00 PM in the afternoon I sighted a male Eastern Least Clubtail. He was extremely wary and with good reason, as a Black-shouldered Spinyleg and a Dragonhunter were active in the area.

However, I waited patiently and sure enough he kept returning to his favourite spot. The dragonfly seemed to become accustomed to my presence and decided I wasn't a threat, and I was eventually able to get close enough to capture some images of this uncommon but beautiful little dragonfly.