Sunday, May 28, 2017

Dot-tailed Whiteface Explosion

On 25 May 2017, Scott King and I surveyed a pond at the River Bend Nature Center near Faribault. His goal was to record Horned Clubtails. I wanted to see a Southern Spreadwing. We discovered clouds of emerging Dot-tailed Whiteface. Over a thousand flew up from the sedges in the pond and a nearby grassy field. 
The first photo shows an exuvia left by a Dot-tailed Whiteface. An exuvia is the cast-off skin of a larval insect, in this case dragonfly. Some insects eat their exuviae, but others leave them behind. The second image is of a teneral Dot-tailed Whiteface perched next to its exuvia. Teneral dragonflies are soft, recently emerged dragonflies. Their colors are often muted and their wings shiny. If they can fly, they often do so poorly. Some teneral individuals have undeveloped wings.
Adult Dot-tailed Whiteface were also abundant at the pond. The photo above is of a male. You can easily see why it is named Dot-tailed Whiteface. Females, like the one below, are handsome dragonflies. They also sport white faces.
This day was one of the first truly warm days of the spring. Temperatures exceeded 80 degrees F. Whitefaces must develop rapidly. Already a few flew in a wheel-shaped wheel position over the pond. The male holds on to the back of the female’s head, preventing competing males access to her. The male then transfers sperm from his genitals at the end of his abdomen to a sperm holding pouch, his seminal vesicle, near the front of his abdomen. The female attaches her abdomen end here and collects the sperm in her abdominal pouches. Males may continue to guard their mates or the males may fly off. Competing males, upon mating with a female, are likely to flush out her seminal pouches. Females can carry sperm from a single mating for the remainder of their lives, fertilizing their eggs when suitable habitat is encountered.

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