Aeshna canadensis

Walker, 1908

Canada Darner

Aeshna canadensis, the Canada , is a large in the . First described by Edmund Murton Walker in 1908, it is common throughout southern Canada and the northern United States. are active from June to October. The species has been documented undertaking north-south migratory movements within its range, representing the first conclusive evidence of in the Aeshna in North America.

Aeshna canadensis by (c) Nick Block, some rights reserved (CC BY), uploaded by Nick Block. Used under a CC-BY license.

Aeshna canadensis by the Smithsonian. Used under a CC0 license.

Pronunciation

How to pronounce Aeshna canadensis: /ˈiːʃnə kæˈnædənˌsɪs/

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Identification

Distinguished from the very similar green-striped (Aeshna verticalis) by minor differences in the shape of the thoracic markings; green-striped darner typically has green stripes. Separated from the larger lake darner (Aeshna eremita) by the latter's distinct dark stripe across the . The notched thoracic stripe with extension at the top is a diagnostic feature for A. canadensis.

Images

Appearance

are relatively large, slender , 64–73 mm in total length. Predominantly dark with paler or green markings. has two vertical stripes on each side; the stripe has a prominent notch with an extension at the top. has spots on most . Pale markings are usually blue in males and range from -green to blue in females. are bluish in males and yellowish or bluish in females. Pale markings may turn gray at colder temperatures.

Habitat

Larval includes lakes and ponds, particularly bog ponds and beaver ponds with abundant emergent vegetation. Breeding ponds typically have acidic conditions; one Ontario study found the restricted to ponds with pH ≤ 6.2. foraging habitats include clearings and roadways where feeding swarms form in early evening.

Distribution

Found from Newfoundland and New Jersey in the east to Yukon in the west. Range extends south down the Appalachian Mountains to West Virginia and through mountain ranges to California and Montana. Isolated in Nebraska. Core range spans southern Canada and northern United States.

Seasonality

observed from June to October. occurs May–June in central Minnesota, with mature adults flying and ovipositing in late summer following a 10–15 week maturation period.

Life Cycle

Aquatic stage occupies most of the life span. found in lakes and ponds, especially bog ponds and beaver ponds. Larvae may spend one or two winters underwater before emerging. occurs May–June. undergo 10–15 week maturation period before reproductive activity.

Behavior

Mating occurs in shrubs near breeding ponds. Females lay at water level, usually in marshy vegetation away from shore. Breeding most active in sunny weather. Adult males slowly along pond shores, sometimes dropping to the surface to search for females. Away from breeding sites, adults form feeding swarms with other in early evening. Some undertake north-south migratory movements; late-flying mature adults in Minnesota have been traced to origins in southern Manitoba and more northerly regions.

Ecological Role

Predatory ; feed on small aquatic . are aerial . is considered common to abundant where found.

Similar Taxa

Aeshna verticalisGreen-striped ; very similar but distinguished by minor differences in thoracic marking shape and typically green stripes
Aeshna eremitaLake ; larger size and distinct dark stripe across the

More Details

Migration Evidence

Stable hydrogen isotope analysis of tissue (δ2Hw) combined with phenological observations provides conclusive evidence of north-south . Late-flying mature in Minnesota originated from southern Manitoba; adults collected in northern Minnesota and south-central Canada originated from central Canada (Manitoba/Quebec) or northeastern range areas.

Acid Sensitivity

Ontario study documented restriction to breeding ponds with pH ≤ 6.2, indicating sensitivity to water chemistry and potential vulnerability to acidification.