dragonflies mating

WaterLine photo by Capt. Josh Olive

A pair of wandering glider dragonflies (Pantala flavescens) working on making more dragonflies. Afterward, they’ll probably want a snack, and it will probably be mosquitoes.

Wet summer weather is here, and it’s bringing out biting insects in force. Wander outside in the morning or evening and see how long before you get your first bite. The tiny draculas are even active in the middle of the day. Welcome to Florida, sucker.

For as long as people have been in the Sunshine State, they’ve been trying to find ways to stop biting mosquitoes. It’s always been a losing battle, but modern chemistry has given us specific poisons (larvicides that target the aquatic juveniles and adulticides that kill the ones already flying around) that impact mosquitoes specifically. Well, that’s the claim, but I sure see a lot fewer insects of all kinds than I did 25 years ago.

Wars are always full of rumors and propaganda, and the fight against bloodsuckers has been no different. All around the United States, hundreds of thousands of property owners have erected purple martin houses. While some just like having the birds around, the big reason is for mosquito control. This is because they say a single purple martin can eat 2,000 mosquitoes a day.

That’s an impressive figure. But who exactly is “they?” According to a report by the Purple Martin Conservation Association, the origin of the confusion was a paper authored by J.L. Wade in 1966. When writing about the purple martin’s rapid metabolism, Wade made the assumption that the bird must consume its weight in mosquitoes on a daily basis to sustain itself. Yet he presented no actual evidence — just a very bold and unsubstantiated claim.

Why would he reach such a conclusion? Perhaps it’s worth mentioning that he was a businessman, not a scientist, and it was in his financial interest to get people on board with attracting purple martins: Mr. Wade sold kits for building purple martin houses. And I’ll point out he didn’t actually lie. He didn’t say martins DO eat 2,000 mosquitoes a day — he said they CAN.

This is a good example of what happens when people repeat things they’ve heard or read with no critical thinking involved. But if you look into the actual behaviors of these animals, Wade’s claim falls apart pretty quickly.

Purple martins prefer to feed during the day; mosquitoes are mainly active after sunset and before sunrise. Martins prefer to feed on the wing 50 to 200 feet in the air; mosquitoes rarely fly at such heights. Studies of martins over the past 50 years have consistently shown they target larger insects; mosquitoes are small. While they do eat a few, it’s a tiny percentage of their diets.

Despite this, there are people reading this column right now and shaking their heads at how wrong I am. With so much clear opposing evidence, why do people still believe that purple martins are great mosquito control?

It’s very simple: Human beings are amazingly skilled at believing what we want to believe. Even in a non-election year, it’s easy for us to look right through a mountain of facts that dispute a deeply held personal conviction. It’s one of our major flaws as a species.

Here’s another fact you won’t believe: Bats are lousy mosquito control, too. Now, I’ll readily admit this one is more believable. Bats fly in the evening, and we’re usually starting to see them about the time we start slapping skeeters. They also fly low, sometimes even darting above people’s heads as if to grab the mosquitoes we’re attracting.

But again, what do the studies show? Moths and beetles are far and away the top prey choices for local insect-eating bats. Sure, they eat mosquitoes. They also eat houseflies and winged termites. But they don’t focus on them because they’re just too small.

A bat burns through a lot of calories for its size. If they relied on mosquitoes, they’d have to eat them nonstop. Imagine trying to survive on green peas — only you have to hunt them down individually. How long you gonna live?

OK, how about mosquitofish (or gambusia, if you prefer)? Charlotte and Sarasota counties will provide them to homeowners to put in their ponds, cisterns, rain barrels, horse troughs, etc. Surely they must work if the government is spending money on them.

Yeah, they work. Well, sort of. Here’s the thing about mosquitofish: They’re native. They occur in large numbers here in the wild. In fact, they’re one of the most common freshwater fish in our canals, rivers and lakes. If they really were great mosquito control, there wouldn’t be any mosquitoes here naturally.

Mosquitofish will eat mosquito larvae. If you expect them to eat lots of mosquito larvae, eliminate their other food sources. These tiny guys eat almost any animal-based food they can get in their eensy-weensy mouths. The eggs and fry of other fish are a particular favorite, and they’ll even eat their own offspring.

In the confines of a rain barrel or livestock trough, they’ll eat whatever mosquito eggs and larvae show up. In more natural conditions, those are again just a small part of their diets.

However, there is one creature that gobbles mosquitoes like no other. As juveniles, they live in the water and feast on (among other small critters) mosquito larvae. As adults, they are a mosquito’s worst nightmare, zooming in from above to scoop them up by the dozens.

This ultimate mosquito attack weapon is the humble dragonfly. Few if any other predators kill as many mosquitoes as dragonflies do.

Now for a heaping tablespoon of irony. We put up martin houses, bat houses and stock mosquito fish as part of our efforts to rid ourselves of these pests, then pat ourselves on the back over a job well done. But what are we really doing?

Martins that hunt near water consistently take large numbers of dragonflies — far more than they eat mosquitoes. Bats that dive down to grab insects near us in the evening are often grabbing not mosquitoes but dragonflies. Watch closely the next time this happens near you. We stock every yard pond and rain barrel with mosqutofish. Mosquitofish are a major predator of dragonfly eggs and freshly hatched dragonfly nymphs.

The more we try to bend nature to our will, the more things go awry. We’d have been better off letting things take care of themselves rather than imagining humanity to be the lords of all creation. The more clever we become, the more foolish we are. The more we think we know, the more it turns out we know nothing.

Capt. Josh Olive is a fifth-generation native Florida Cracker and a Florida Master Naturalist, and has been fascinated by all sorts of wild things and places since he was able to walk. If you have questions about living with wildlife, contact him at Publisher@WaterLineWeekly.com or 941-276-9657.

Capt. Josh Olive is a fifth-generation native Florida Cracker and a Florida Master Naturalist, and has been fascinated by all sorts of wild things and places since he was able to walk. If you have questions about living with wildlife, contact him at Publisher@
WaterLineWeekly.com or 941-276-9657.


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