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On walks in the Campus
Natural Areas, most of us have probably noticed long slender and
colorful bugs, like winged darning needles, hovering in the air, often
over the water. We recognized them as dragonflies and walked on. Now
perhaps it’s time to take a closer look at this marvelous creature.
Meet the Insect
Of the order Odonata, dragonflies have three body parts: head,
thorax, and abdomen. Their six legs and four wings also characterize
them. They pass through several stages before they appear as the winged
creatures that we see about rivers and ponds. Eggs, laid in or near
water, hatch into larvae. “Odonata” means “toothed jaws.” These small
insects are tough predators. In fact, in the larval state, they are the
top of the food chain in ponds and streams, after the fish.
At the appropriate time, the larvae undergo a metamorphosis and
become the familiar dragonfly that we notice. The newly hatched
dragonfly, known as a teneral dragonfly, moves away from the water to
mature. At this stage in life, it is very susceptible to predation from
creatures, such as birds. When mature, the dragonflies return to the
water to mate and the cycle begins again.
Where are they now?
Certainly if you walk the Campus Natural Areas now, you will not
see any dragonflies. So just where are they? Most are overwintering in
the larval state, but one common Wisconsin species, the Common Green
Darner, has migrated south for the winter. Dragonflies can begin to
appear as early as April, but the best time to see dragonflies in the
CNA is from June through September.
Dragonfly Watching
Your search for dragonflies will be greatly enhanced by a pair
of close-focusing binoculars. Ideally the binoculars should be able to
focus at a distance of 8 feet, and 4 feet is even better. Once you have
spotted a dragonfly, to know what species it is, consult a guidebook,
such as Common Dragonflies of Wisconsin by Legler and Westover
(available from the author) or Dragonflies through Binoculars by
Dunkle.
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Within the CNA,
recommended places to check for dragonflies include the 1918 Marsh and
the Biocore Prairie. If you want to see dragonflies in the CNA, it is
best to look on a sunny day.
Expected Dragonflies in the CNA
In Wisconsin, 110 species
of dragonflies have been recorded. Some common local species to expect
to see in the CNA include Common Green Darner, Black Saddlebags, and
Twelve-spotted Skimmer. Common Green Darners fly constantly, but their
green thorax and bright blue abdomen are easily recognized. The dark
wing spots near its body make the Black Saddlebags appear to carry
saddlebags, hence its name. This tiny insect can fly at 17 miles per
hour. The Twelve-spotted skimmer gets its name from the three dark spots
found on each of its four wings. Three other common dragonflies are
Common Whitetail, White-faced Meadowhawk, and Widow Skimmer.
Dragonflies can indicate the
health of a body of water. They are adversely affected by pollution and
pesticide run-off. Since they eat lots of insect pests, like mosquitoes,
we ought to keep the habitat healthy for dragonflies.
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Methods of Improving Water Quality and
Decreasing Erosion Being Studied
Urban storm runoff brings sediment and
excess nutrients, such as phosphorus and nitrogen, as well as causes
erosion problems in the CNA. An especially dramatic example of storm
water erosion can be observed around the Angler’s Cove Parking Lot in
North Shore Woods. In addition to causing Lake Mendota to be less
inviting to a diverse aquatic community, the nutrients in this runoff
cause unpleasant summer blooms of algae.
CNA staff and UW classes will be cooperating with the
Wisconsin Department of Natural Resources and soil conservation
experts from Dane County to develop plans to decrease and slow down
storm water runoff and prevent erosion.
If you would like more information on or to become
involved in solving these storm water issues, see the Projects section
of the FCNA Web Site at
www.uwalumni.com/fcna or contact
Cathie Bruner at
cbruner@fpm.wisc.edu or 265-9275.
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