Mosaic Season

It’s August, and nothing means August more than the Aeshna darners. Often called the mosaic darners, this genus of large brown and blue or green (occasionally yellow) dragonflies are common across Algonquin Park from late July onwards. They breed in most water bodies from lakes to bogs to streams, but it’s when they are away from the water that things really become interesting, as they gather into large swarms wherever there are lots of flying insects to catch.

The most intense swarms occur in gravely areas on warm, sunny evenings when the reproductive castes of ants emerge. At these swarms it is often possible to catch multiple darners in a single swing. Still, swarms are a regular occurrence in a variety of conditions at various times of day, and individuals and smaller numbers can usually be easily found in any open area on any nice day.

Through much effort and more than a little luck, I’ve managed to see every species of Aeshna regularly found south of the boreal forest already this year. Five species dominate the Algonquin fauna, with another three being much more local and rare.

Lake Darner is common throughout Algonquin, and is often recognisable in flight by it large size and bulk. It is mainly found at large lakes and is very rarely found in evening swarms.

Male

Canada Darner is quite similar but is significantly smaller. It is often very common in the middle of the day at breeding locations, but when foraging away from water often sticks to shady forest edges or late evening.

This dull female Canada was even duller to the cool temperatures. 

Male

Green-striped Darner is nearly identical to Canada, but differs in a number of subtle ways that make them very obvious with a bit of experience. The stripes on the thorax are always almost or entirely green while Canada darners usually have more or less blue thoracic stripes. There are many exceptions however, and the shape of the markings on the thorax and abdomen allow conclusive identification.

I caught this female Green-striped Darner on July 30th at twilight skimming the staffhouse lawn, and have caught two more since. Green-striped Darner seems to be increasing in Algonquin, having gone from essentially absent to become a regular if rare resident in the last decade.

With a green form female Canada.

Lance-tipped Darner is a very rare species in Algonquin, so I was very surprised to catch one on July 31st at the Visitor Centre. This may be only the second record from the highway corridor.

Amazingly, we have since found 3 more individuals in a single swarm - unprecedented for the area.

Black-tipped Darner often dominates daytime swarms in Algonquin. The large, straight. bright thoracic stripes and long abdomen make it very obvious in flight. The all-black final segment of the abdomen is almost diagnostic, although I have seen several Shadow Darners with no markings on the same segment, and Black-tippeds occasionally have very limited markings here.

The well-named Shadow Darner is usually only found in shady areas, and even then only sporadically until the very late evening, when it can become common, often flying with Canada Darner.

The remaining two species have very distinctive thoracic patterns compared to the other local member of the genus. Variable Darner is an abundant species here with the local populations havin 4 spots on the sides of the thorax.

Very rarely, the spots can be joined. I believe this individual is an aberrant member of our local subspecies rather than a vagrant from somewhere else, where populations can have very different patterns.

The most distincitive Aeshna is Mottled Darner. It is rare, likely due to its restricted habitat preference (seemingly large sandy lakes with Pickerelweed). I've seen three in Algonquin so far this year.

This picture was posed by putting the darner in the fridge for a few minutes. Getting shots of naturally perched darners is an extremely difficult task.

Aeshna swarms can innclude a whole host of other species, and even if you are farther south where this genus is rarer, Common Green Darners, Gliders (Pantala) and Saddlebags (Tramea) provide a nice substitute. This is the time of year for it, so grab a net, find a swarm and start swinging!