Colorado River Flow Now Part Of Caddisfly Battle In Bullhead City

By Ron Dungan
Published: Wednesday, September 9, 2020 - 11:48am
Updated: Wednesday, September 9, 2020 - 3:12pm

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Swarming caddisflies
Michael Cavallero
Swarming caddisflies.

Bullhead City is located along the Colorado River, across from Laughlin, Nevada.

The area is known as a place to take advantage of Arizona’s mild winters, to gamble or spend time along the river.

But it had a problem. Twice a year, caddisflies emerge from the river in swarms.

“They don’t bite. They don’t sting. They just are a nuisance. They get into people’s food. They get into people’s ears, noses. They’re all over you,” said Michael Cavallaro, a pest control expert for Bullhead City.

Caddisflies are commonly found wherever there is clean water, but the population near Bullhead City has exploded. Nobody knew what to do about it.

Since caddisflies spend most of their lives underwater, a lot of people have never heard of them. But they are moth-like insects with tiny hairs on their wings.

Cavallaro says some people may be allergic to the bugs. Others report problems with asthma. He suspects it’s those hairy wings.

“But for the most part they’re pretty harmless. There’s just too many of them,” he said.

Jackie Mazzeo, a spokewoman with the Laughlin Chamber of Commerce, said the bugs are a problem for tourism. 

"They don’t bite. They don’t sting. They just are a nuisance."
— Michael Cavallaro, Bullhead City pest control expert

“It’s bad. When they emerge in the spring and they emerge in the fall, they swarm in balls, along the riverwalk," she said.

Balls of caddisflies did not go over well with tourists, who started to complain. Mazzeo said that was when they knew they had to do something.

So Bullhead City hired a pest control expert a few years back. Cavallaro came on board last summer.

He says the idea is to knock down the number of bugs without relying too heavily on pesticides.

“Basically what we’re looking for is kind of like a multi-dimensional approach," Cavallaro said, "to reducing and suppressing their numbers to a pest-tolerant threshold. So, essentially what can people take, and what can the ecosystem do without?”

Caddisflies spend most of their lives on the bottoms of lakes or streams. The larvae build houses out of pebbles, dirt and shells.

Some carry their houses on their backs, like tiny hermit crabs. The ones that live near Bullhead City don’t do that.

They're known as Smicridea fasciatella. And they build tiny houses, but they don’t carry them around. They spin silk nets to capture food.

When the larvae mature, they grow wings, rise to the surface and fly away. It’s during this journey that they become a source of food for trout. One reason there are so many bugs is because a nearby fish hatchery fell into disrepair. 

“We had to buy trout from fish farms and stock the river to help us control some of the caddisfly larva, because they feed on it.”

Casey Kuhn/KJZZ
An example of how caddisflies invade riverfront properties in Bullhead City.

Buying trout was expensive. The hatchery has been repaired, but there are too many caddisflies for the fish to make much of a dent. In addition to trout stocking, Cavallero said they have also looked into pheromone traps, and insecticides on paint. Then he hit on the idea of lowering the water flows. He ran tests to see if it would work.

“There are a number of other things that we’re kind of starting to pilot but one of those that has the most promise, and has shown to be pretty effective as far as the reduction in numbers is lowering the Colorado River," he said. 

The idea was to lower the flows while temperatures were still warm enough to dry out the caddis larvae. That required buy-in from local merchants and the Bureau of Reclamation, local tribes and others. They were able to do it, and on Aug. 27, the first of two flow reductions took place. When the river dropped, people pitched in for a day of river cleanup.

And they found things. Trash. Cellphones. Some of them still worked.

“Glasses and wallets and anchors and a bull’s skull, and a sunken — believe it or not — life vest. And jewelry. Now you can only imagine, missing swimming suit bottoms.”

Mazzeo is optimistic that the flow reduction will work.

“What we’re planning on, is an 80% decrease in swarming and the emergence, which is the difference between people walking along the river and enjoying their vacation, or swear they’re never coming back.” 

The next flow reduction will take place Sept. 10.

Shot of the Colorado River during the low flow
Michael Cavallero
The Colorado River during the low flow period on Aug. 27, 2020.

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