Friday, July 19, 2002
Biodiversity Corner: Blue Dasher Dragonfly
When and where seen: On July 10 at the Cranberry Bog, on July 11 and 12 in the garden on School Street.
Identification: The male is blue with a black tip and has green eyes, while the female is dark with paired yellow streaks down the top of the abdomen. It belongs to the group known as skimmers.
Occurrence: The Blue Dasher is one of the commonest dragonflies and is easy to observe because it tends to land frequently, on any stick or twig in the garden
Observation: During July dragonflies are abundant in Carlisle and it is not too difficult to identify many of the commonest species. Recently published field guides have made this fascinating activity much easier. A group of experienced and novice observers, armed with butterfly nets, close-focusing binoculars and field guides, identified 16 species at the Cranberry Bog on July 10. These beautiful insects, commonly called "odes" because they belong to the class Odonata, are found in backyards and gardens, as well as along streams and ponds. Odes include damselflies which are usually smaller and land with their wings closed, while dragonflies can be over 3 inches long and land with wings spread open. The Blue Dasher is about 1.4 inches long.
Temperature Control: Dragonflies are able to avoid excessive heat by sitting with their abdomens pointing directly at the sun (obelisk position) thereby reducing the area of body surface catching rays. This is not a successful strategy for humans you need an extremely slender abdomen narrower than the width of your head and it definitely helps to have legs attached at the front end of the thorax.
Life of Odes: Female dragonflies and damselflies lay their eggs in the water of ponds, streams and rivers, sometimes into the stalks of plants growing in the water. The larvae persist for one month to 5 years. The larva crawls out of the water, sheds its last exoskeleton and by metamorphosis emerges as a dragonfly or damselfly.
Food: Dragonflies are predators with a voracious appetite for small flying insects. Some specialize in killing mosquitos. Dragonfly legs, very poorly adapted for walking, are superb for catching prey in the air and grasping it firmly while tearing it to pieces with their sharp mouth parts.
References: Stokes Beginner's Guide to Dragonflies by Blair Nikula, Jackie Sones, Donald and Lillian Stokes, Little Brown. Dragonflies Through Binoculars by Sidney W. Dunkle, Oxford University Press. Two excellent Internet sites are: www.odenews.net and www.afn.org/~iori.
More Biodiversity: Additional Spotted Turtle sighting
Thanks to Michelle Lando for reporting a spotted turtle in the Brook Street area. These animals are quite rare and from her photographs we were able to determine it was a different specimen than the one reported in the Mosquito on June 21.
© 2002 The Carlisle Mosquito