Dragonflies Can Help Control Your Pond’s Pest Population

Published on August 29, 2016

This blue dasher dragonfly rests on a native waterlily called Nuphar japonica, or spatterdock.
This blue dasher dragonfly rests on a native waterlily called Nuphar japonica, or spatterdock.

Many people think that installing a water garden or water feature will create a mosquito problem for the nearby landscape. However, I like to talk about the fact that if water is managed correctly, the landscape will actually have fewer of these bugs and other small, flying insects than landscapes without water. Water can attract many kinds of predators that view mosquitoes as one of their main-course meals.

One that is very interesting and beautiful is the mosquito hawk, or as more people may know them, dragonflies and damselflies.

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 Dragonflies and damselflies are both part of the order of Odonata. The main difference between the two is that dragonflies hold their wings out horizontally, while the damselflies hold their wings above their back. Damselflies are generally a much smaller species. The entomologists have grouped these insects into interesting groups like clubtails, darners and cruisers, just to name a few. They are beautiful insects that can hover and dart about, freely at will.

The key message is that correctly managed water will result in a well-controlled mosquito population. Mosquito control strategies can commence at the larval or adult stages.

Larvae Control Strategies

One larval management method is aeration. If the water is pumped, or aerated, mosquito larvae cannot survive. The larvae need to connect to the surface of the water in order to breathe. Pumping the water breaks the surface tension, and the larvae cannot maintain a connection. So your water pump is not only aerating the water, but it is also limiting mosquito reproduction.

Another management tool in controlling mosquitoes involves adding fish to the water garden or container. Fish consider the larvae a delicacy and will search for them relentlessly, devouring all of them.

pond pests
A dragonfly adult emerges from its larval stage, leaving its exoskeleton behind.

If adding fish is not an option and the water is not pumped, adding Bacillus thuringiensis serotype israelensis (Bti) in the form of brand names such as Mosquito Bits or Mosquito Dunks is easy and effective. Bti produces toxins that kill various species of mosquitoes, fungus gnats and blackflies, while having almost no other adverse effect on other organisms. Simply float the Bti product on the surface of the water in order to be effective.

Any one of these techniques will kill 100 percent of the mosquito larvae, but not necessarily the adult mosquitoes that are naturally attracted to water for laying their eggs. Even though the larvae cannot survive, the adults that stick around can easily become a potential problem.

Adult Control Strategies

Enter the mosquito hawk, or dragonfly. Like mosquitoes, mosquito hawks are also naturally attracted to the water to lay their eggs. While there, they survive on meals of mosquitoes and other pesky, small, flying insects. The flying adults can catch them in their legs, which dangle downward like a net. Even more interesting, the dragonflies lay their eggs in the water, so once they hatch, the dragonfly nymphs may also eat any mosquito larvae still present on the surface of the water.

There are other mosquito predators that are about as interesting as dragonflies — birds, like purple martins and barn swallows, bats, frogs and toads, just to name a few.

Create the Ideal Habitat

Simple things attract mosquito hawks, such as some marginal plants. Each species has different egg-laying strategies that may require a certain type of plant stem to lay their eggs. Some will lay eggs closer to the water surface — if not directly in the water, on the stem. Some will even lay their eggs on waterlily leaves or lotus stems. Others may like wood that submerges into the water for laying their eggs.

Blue Dasher Dragonfly clinging to a phragmite
Photos by Greg Courtney, Carl Kurtz, Nathan Brockman and Jamie Beyer

Skimmer boxes and pump intakes end up killing a lot of dragonfly nymphs by sucking them in. Providing different mechanical filters before the pump intake may allow more dragonflies to survive.

Fish are a natural predator of the dragonfly nymphs. The larger the fish, the larger the nymphs they can eat. All fish will eat the small, newly-hatched nymphs. This simply is unavoidable if you have fish, so providing a variety of habitats is always the best solution, giving the nymphs more places to hide.

A category of pond called wildlife ponds will promote and provide the greatest variety of habitats for the greatest number of wildlife species, including dragonflies. These ponds usually have a sloping edge and lots of driftwood going into the water. The pond may also have a sand or mud beach. Certain dragonflies seek out this type of habitat.

There are some species of Odonates that live for five to seven years in the nymph stage, while others’ life cycles will complete in a single season. Those that survive over the winter can do so in either the nymph or egg stage on the stems of plants, on wood, or in muck, depending on the species. Cleaning the muck or sediment out of a pond could end up killing a lot of dragonfly and damselfly larvae.

Welcome the Frenzy

dragonflys mating pond insects
These two ebony jewelwing damselflies are coupled together for mating. The female has the white spot at the tip of its wings, and the male is more brightly colored. Notice that the damselflies’ wings are held above their bodies, whereas dragonflies hold their wings out horizontally.

An interesting habit of some species of adult dragonflies is their ability to swarm. Literally, tens of thousands can hover above the ground eating small, flying insects — including mosquitoes. Usually in the late afternoon, there might be a dragonfly in every square meter of air above a prairie, for example. Think of it as a feeding frenzy of sharks.

So, as I often like to say to people, if you have well-managed water in your landscape, you will have fewer mosquitoes than dry or poorly managed landscapes. The dragonflies will take care of many of those that dare to show up!

Now, when you hear people express the perceived notion that mosquitoes will be a huge problem in any water environment, you can explain why this does not have to be the case. While there are many different reasons, one of the most interesting and beautiful is the mosquito hawk. They are a welcome addition to anyone’s landscape.

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