Loon Update and Dragonfly Myth

Little Phyllis is celebrating and growing fast!  Below are Phyllis and Phineas on July 2nd.  Phineas (left) hatched about a day and a half after Phyllis, and still has some catching up to do.

Here they are on July 11th, just 9 days later!  They are being fed bigger minnows, and below, a good sized crayfish.  

We often see our chicks being fed crayfish.  Below Dad is bringing another one.  Crayfish are rich in protein and minerals and easy to catch.

After being stuffed with crayfish and minnows, the chicks get sleepy.  This little one is trying to keep its eyes open.

Phineas (left) is a little further away than Phyllis, but is clearly smaller and has a different shape than its older sibling. Though we have not recently witnessed the two chicks fighting, we saw Phyllis claiming her dominance in just the first few days. Phineas tends to hang back when Phyllis is being fed, but always seems to get a share in the end. We have lost several chicks over the past few years from sibling rivalry, but always within the first two weeks. Phyllis and Phineas are now 21 and 22 days old. We are hopeful that both chicks will survive.

You have probably seen the claims that dragonflies eat 100 mosquitoes a day and thus will help control mosquitoes in your yard, especially if you plant flowers they are attracted to. There is simply no basis in fact for these claims, and Jon, who has studied dragonflies and damselflies for over 30 years, will explain why.

Remember, the term dragonfly refers to the insect order Odonata, which includes both dragonflies and damselflies. Dragonflies (left below) always perch with wings spread and have large eyes, often meeting on top of the head. Damselflies (below right) keep their wings together or slightly spread when perching and their smaller eyes do not meet on top of the head.

Dragonflies are voracious hunters of a wide variety of insects, including mosquitoes and other dragonflies. Below are two damselflies feasting on insects they caught in Turtle Cove. One is a female Eastern Forktail (Ischnura verticalis) eating a newly emerged insect (not a mosquito). The other is a Spreadwing (Lestes sp.) eating a Bluet (Enallagma sp.).

A recent search of the literature on adult dragonfly diets suggests that mosquitoes are probably a minor part of adult dragonfly diets - less than 3% by some estimates. Most dragonflies could not even fit 100 mosquitoes in their guts.  The major part of dragonfly diets are midges and gnats. So why are mosquitoes not a more important part of dragonfly diets?

A major factor is that mosquitoes and dragonflies are not active at the same time of day.  Dragonflies use vision to find their prey and are generally most active between mid-morning and mid to late afternoon. Mosquito activity peaks around dawn and dusk. Mosquitoes get most of their food by sucking juices from plants. Only female mosquitoes need a blood meal to produce eggs. The ones that bite us find their prey by following odor trails of CO2 and other chemicals released by mammals. These factors make it hard for dragonflies to find mosquitoes during the day.

What about planting flowers that attract dragonflies?  Even if they don't eat 100 mosquitoes a day, surely they will eat some? Let's explore what attracts foraging dragonflies. There are three types of dragonfly foraging behavior: perching and watching the sky for flying insects, cruising in the air in search of them,  and searching among plants for insects sitting on foliage.

What the perchers need is a place to sit from which they can see a large expanse of sky. Below, a male Calico pennant (Celithemis elisa) perches on a tall grass stem. You can see its large eyes cover most of its head. The thousands of facets in each eye allow it to detect motion and track moving insects.

Most of the perchers in your yard will be females. Below, a female Slaty Skimmer (Libellula incesta) is watching for food that she needs to produce a batch of eggs. She will stay away from the water to do that; otherwise, she would continually be harassed by males seeking a mate. 

Below, a male Slaty Skimmer perches on a stick overlooking our pond. He is scanning for food, other males to chase away, and females to mate with. No flowers are needed.

Cruisers spend most of their time in the air, either foraging away from the water or flying circuits over the water searching for mates. Your best chance of getting close to one is to find it hanging from a branch where it spent the night, like the female Arrow Clubtail (Stylurus spiniceps) among our blackberries.

Most damselflies are perchers, but some, like the Bluet below, will search among the vegetation and grab insects off leaves rather than catch them in midair. The insects they are looking for are not likely to be on the flowers. So, dragonflies in your yard will bring you joy but not take away many mosquitoes, and you do not need to plant so-called dragonfly-attracting flowers. None of those in this newsletter are sitting on flowers, and we very rarely see them on flowering plants.

The best way to attract dragonflies is to have a pond in your yard or nearby.  All but two of the dragonfly photos in this newsletter were taken in our backyard. Much of the yard is a natural meadow, and we have a small pond. Those two features  give us more than a dozen species of dragonflies each summer. Mosquitoes tend to avoid ponds that have lots of insects and other animals that would eat their larvae.

The best way to attract mosquitoe is to have standing, stagnant water in your yard. A bottle cap, unattended bird bath, clogged gutter, old tire, or anything capable of holding water and attracting microorganisms that become mosquito food will bring you lots of them. 

So far, the focus has been on adult dragonflies and what they eat. The larvae of dragonflies will consume mosquito larvae, and there have been a number of efforts to use them for biological control in ponds and other aquatic situations where disease-carrying mosquitoes are present. So far, most efforts have not had much success. Those that have done best depended on having a healthy pond with abundant fish and insect predators of the egg, larval, and pupal stages of mosquitoes. 

Two reminders:

Less than 0.25% of insects attracted to bug zappers are mosquitoes. Bug zappers are very good at attracting and killing beneficial insects. 

Fogging or chemically treating your yard is only effective until the next generation of mosquitoes arrives. Locating and removing standing, stagnant water is far more effective.