Tuesday, September 16, 2014

Lake Darner (Aeshna eremita)

At first glance the Lake Darner looks very similar to the Canada Darner. The main distinguishing characteristics are the distinct dark cross-stripe on the face, the very deeply notched anterior thoracic stripe and a second thoracic stripe that is relatively broad compared to other Aeshna species.

On the average Lake Darners are larger than Canada Darners; this male measured 75 mm in length. In addition the cerci of Aeshna eremita are strongly bent upward and bear prominent bumps on the upper surface, but without a Canada Darner handy to compare these features to the differences were not obvious in the field.

A female Lake Darner, at 72 mm almost as long as the male encountered on September 15th. The field marks are right on the money and identical to those of the male, with a notched (the notch being nearly semi-circular) first thoracic stripe and wide second thoracic stripe ...

... a central line on S2 joining the band on S1, and fused blue spots on S10 (the male deviated on this feature, his were touching, but just barely).

A closeup of the face depicting the cross-stripe.

The terminal appendages (cerci) are rounded at their tips and similar to those of the female Canada Darner. Again, note the fused blue spots on S10.

Details of the genital plate and styli, however, these features aren't useful for separating this darner from other related species (at any rate, they are not mentioned in field guides).

The Lake Darners encountered thus far have been unbelievably tame. The female had captured an insect and, looking for a place to sit and eat it in peace, tried perching on my face twice. A male (perhaps attracted to the female?) stopped to perch in the tall grass within arm's reach as the female was being photographed.