Dragonflies are Good Insects--They Eat Mosquitos

Dragonflies among beneficial insects

Bill Sevier: Ask a Master Gardener  

Saturday, August 27, 2016

Q: I have a pond and there are a number of dragonflies on the plants around it. They often hover over the water dipping their tails into the water. Are they harmful? N.D. Tulsa

A: These insects are not harmful, indeed they are grouped into the category of “good insects,” and they eat the “bad” insect pests.

There are several common names for these insects, which are related to myths. One is “snake doctor,” commonly used in the South. It is related to the myth that they are able to repair injuries of snakes. There are other names, such as “devils needle” and “water witch,” but the proper name is dragonfly. The name dragonfly comes from a belief that they are reincarnation of dragons. If you look at a dragonfly up close, one can see where the “dragon” part of the myth came from.

Dragonflies are classified in the order Odonata and have been with us for millions of years. There are fossils showing evidence of some dragonfly species with wingspans up to 30 inches across. The largest living dragonfly has a wingspan of about 7 inches and locally the largest has about a 4-inch span.

The adult female dragonfly lays eggs either in water or plant material near water. The eggs hatch into nymphs, and they end up in water where they may live for up to 5 years. The nymphs are large, often 1-2 inches in length; they feed on other insect larvae (especially mosquitoes) and sometimes on tadpoles and small fish fry. After maturing, they leave the water and develop their adult form.

Adult dragonflies live weeks to months and spend their time reproducing or feeding. They are fast and agile fliers that are able to catch other insects in the air. They catch and eat large numbers of mosquitoes, flying ants and termites, moths, butterflies and other insects.

Also in the Odonata order and seen in the same environment as dragonflies are their cousins, damselflies. These are generally smaller and at rest usually fold their wings over their back, rather than keeping them outstretched as dragonflies do. Many are blueish iridescent. Their feeding and reproductive behaviors are similar to dragonflies. Two damselflies are commonly seen coupled while flying as a part of reproduction behavior.

The dragonflies, like all beneficial insects, need to be protected. Their status is being threatened by loss of habitat and use of insecticides. Do your part in caring for these insects by avoiding indiscriminate use of any insecticide. They, in turn, will help you keep down the population of mosquitoes.

Garden tips

• Always follow directions on the labels of synthetic and natural pesticide products. Labels will always list where the product may be used and which pest it is certified to cover. If you spray pesticides, do it early in the morning or late in the evening after bees have returned to their colony.

• If your tomatoes are too tall and gangly, now is a good time to prune the top of the plants by as much as 1/3 to ½, depending on the plant. This will stimulate new limb growth and new fruit production after it cools.

• Reseeding fescue is best done from mid-September through mid-October. If you plan on reseeding, begin scouting for good seed. There is no “best” variety. Purchase a fescue blend of 3 or more varieties, with or without Kentucky bluegrass. Read the label on the seed bag. A good blend will have 0.01 percent or less of undesirable “other crop” seeds.