Vol 107 (2010)

Journal of the Entomological Society of British Columbia


Cover Page

COVER: Aeshna interrupta Walker (Odonata: Aeshnidae)

Aeshna interrupta (Variable Darner) is one of the most common large dragonflies in British Columbia. It is a boreal species, ranging across North America from Newfoundland to Alaska and south in the western mountains to California and New Mexico. It lives in marshes and peatlands and is the typical Aeshna of grassland ponds and lakes in the Interior. On the Coast it is one of the predominant dragonflies in peat bogs.

The scientific name "interrupta" refers to the shape of the stripes on the sides of the thorax. In eastern North America and on the Pacific coast, these are "interrupted", that is, each is broken into two spots. On the Great Plains and in the BC Interior, the stripes are unbroken but thinner than in any other species. The common name "variable" describes these stripes. The stripes and spots of the male are blue; those of the female are blue or, more commonly, yellow.

Most dragonflies spend the majority of their lives in the aquatic larval (nymphal) stage. After about 10 to 14 moults, depending on the species and environmental conditions, the fully grown larva metamorphoses into an adult inside its last larval skin, then crawls out of the water. Now exposed to air, the dragonfly begins its final moult -- the top of the thorax splits open and the adult squeezes out. It pumps blood into its wings and abdomen, which expand slowly, and gradually the body hardens. After an hour or two the dragonfly can fly, but only weakly at first. It leaves the empty larval skin, the exuvia, clinging to the support.

Photograph details: Male Aeshna interrupta photographed during emergence at a grassland pond near Riske Creek, Chilcotin region, BC, 15 June 1978. Pentax Spotmatic II with 50 mm/1.4 Macro Takumar lens, handheld and with available light. Kodachrome 64 film. Robert A. Cannings.