Monday, August 9, 2010

Canada Darner (Aeshna canadensis), Black-tipped Darner (Aeshna tuberculifera) and Shadow Darner (Aeshna umbrosa)

This Canada Darner (Aeshna canadensis) is an immature female, and also a bit cold, so it lacks the depth of color of a mature adult. A large dragonfly, the Canada Darner is about 70 mm long. The photo was taken at Stoco Lake.

Note the styli in this closeup of the terminal abdominal segments.

The notched thoracic stripe is visible in the following lateral views. Also note in the third image that this darner has no facial cross-stripe. The absence or presence of this feature can often be a quick means of sorting out similar darner species in the field.

The exuviae in the next series of images, discovered a few feet away on another tree, likely belongs to the darner above. This find provided an opportunity to obtain pictures of the hinged labium unique to odonate larve.

The colors are pale and the light isn't the best, but the notched thoracic stripe and lack of a facial cross-stripe can be seen in this teneral female, encountered not far from where the female above was photographed.

Darners often forage a fair distance from water and this female lost its bearings and got trapped a window. This is generally game over as the heat will quickly exhaust and kill the insect. The dragonfly was extricated and I took advantage of the chance to capture the beautiful green, turquoise and blue of a mature Canada Darner, after which it was released to continue its journey.

There is a bit of reasonable doubt in my mind as to species and it's possible that these "Canada Darners" are actually the closely related Green-striped Darners (Aeshna verticalis). I haven't had many close encounters with either kind of dragonfly and lack the experience to be proficient at distinguishing the two. Here are a couple of tail end views ... you be the judge.

This male Black-tipped Darner (Aeshna tuberculifera) was the victim of a collision with a vehicle. The thorax was too badly damaged to make out the stripes but enough of the insect's other key field marks remained intact enough to be worth imaging. Black-tipped Darners attain a length of about 70 mm. Note the the cross-stripe on the dragonfly's face.

Views of the claspers and all black terminal segment S10.

This female Black-tipped Darner was encountered along the Eastern Ontario Trail in August of 2008. The female below was photographed perching alongside the trail a few kilometers west of town; again note that S10 is completely black.

I couldn't get any images of the distinctive walking cane shaped thoracic stripes of this male Shadow Darner (Aeshna umbrosa) because it too was hit by a car. The face lacks a cross-stripe although it may show a thin brown line as in this specimen. Shadow Darners are about 75 mm long but relatively slender compared to their other large darner cousins.

The next set of images depicts lateral, dorsal and ventral views of the terminal abdominal segments. In lateral profile the cerci are spatulate with pointed tips, similar to the claspers of the Lance-tipped Darner. However, these organs appear quite different in the two species when viewed from above or below. The Shadow Darner's abdominal spots are greenish and much smaller than in other Aeshna species, giving this dragonfly a dark aspect.