Saturday, August 29, 2009

Migrating Dragonflies

Have you been noticing dragonflies lately?

This information is provide courtesy of Forrest Mitchell, Professor of Entomology with Texas AgriLife Extension. Forrest has a site & a book on dragonflies.

"Although there are a lot of different species of dragonflies and damselflies in Texas (currently 231 according to Odonata Central, see below) not many of them will pick up and migrate as you have already noticed by the stable numbers in your backyard. In the appendix of A Dazzle of Dragonflies are 26 (I think) species listed that may be migratory, but there are two species mainly responsible for these current mass movements that I am seeing: the wandering glider (Pantala flavescens) and the spot-winged glider (Pantala hymenaea). My best scans can be found here:
about halfway down the page.
You can see more pictures and scans of them here:
You can find write-ups on both species here, as well as the 'Species of Texas' checklist:
Odonata Central and John Abbott are where I go with my questions.

The rainpool gliders are adapted to breeding in temporary water, hence their name. If they have enough to eat, the wandering glider can go from egg to adult in less than 30 days during the summer, so the water only needs to last that long. A dozen or so spot-winged gliders developed in a shallow fountain one summer on my deck. I don't know how long it took since I didn't notice them until they were over half-grown. They ate insects that fell into the bowl, midge larvae and any other dragonflies that were deposited after they were. Rainpool gliders will lay eggs in nearly anything that can hold water including buckets, saucers, flower pots, water troughs (a favorite), puddles, ditches and swimming pools. They will attempt to lay eggs on shiny car hoods, wet asphalt and wet concrete. I have noticed that the wandering gliders will lay eggs in water that is in open sunlight, while the spot-winged glider will lay in the shaded pools and water.

A lot of the South is in a drought, but these dragonflies are able to stay aloft for long periods of time and do not need to originate from a close-by source. In fact, the wandering glider is found throughout the world except where it is too cold year-round. Work in the last decade on the eastern seaboard of the US shows that moving dragonflies are swept together and collected by weather fronts. These concentrations may then be deposited elsewhere and a long way off. We have had several cool fronts along with heavy localized rain to make rainpools and either or both may be what accounts for the presence of so many dragonflies in our region. I am noticing them mostly over stretches of roads and parking lots or wide open fields where the hunting is good. They may be in other places as well, but harder to see.

Just as fronts can bring dragonflies, fronts can also take them away. Enjoy watching them while you have a chance. In case they disappear, I've enclosed a scan of another migratory species, the common green darner to look at. They tend to move in September-October in our part of the world and are often seen by people doing monarch counts during the butterfly migration. I had another letter asking me about this species, so I pulled it out and made it a workable size. Feel free to post it on the DMN website for your readers and/or print it in your column. Credit James Lasswell, my coauthor on the book, with its construction. If printed on glossy paper with a good inkjet or laser printer, it is suitable for framing. Or so I think, but then I am biased."

Monday, August 3, 2009

Structural Pests Presentation- August 20th 2:30 p.m.

Take a break from the garden, come in from the heat and learn about the critters you may find inside your house.

What- presentation on structural pests (cockroaches, ants, pantry pests, etc.)
Where- Travis County Extension Office (1600-B Smith Road Austin, TX 78721)
When- August 20, 2009 2:30 p.m.

You'll learn how to identify pests as well as management practices.

For more information, contact Wizzie Brown at 512-854-9600.