Caddisflies

Living near a body of water, including water conveyance canals, is an appealing proposition to many people.  In the case of the CAP, the sights and sounds of water can be very attractive, recreational trails are easily accessible, and houses can't be built directly behind your property.   However, what most of us forget is that water is also attractive to wildlife and is home to a multitude of insects and other organisms.  One of those insects is the caddisfly, which is closely related to butterflies and moths, but spends a majority of its life in water.  Caddisflies are found in moving water throughout the world and are considered to be indicators of a healthy aquatic ecosystem.  Although they are harmless to humans and our pets, they can be quite an annoying nuisance when they emerge from the water in spring and fall.


Caddisfly Life Cycle
Caddisflies

Larval caddisflies feed on algae and mature in the water for as much as ten months.  Changes in water temperature trigger the caddisflies to build a casing (made of silk and sand) in which they "pupate" for several weeks.  They emerge from these cocoons as adults and can survive for several weeks to mate.  During this time, they do not eat, but are still able to drink.  As a result, they can be found in larger numbers near backyard pools, especially where there is ample vegetation to avoid the heat of the day.  In Arizona, we see the primary emergence of caddisflies in May and September, and they are most active at dawn and dusk.  After mating, females return to the canal to lay their eggs and start the cycle all over again.


CAP's Approach

Caddisflies are extremely important to the aquatic ecosystem because they are an integral component in the food chain.  Not only are they a food source for many species of the fish, they also filter much of the algae and other organisms in the water that can cause taste and odor problems.  Regardless of the importance of caddisflies to the environment, scientists have been trying to control nuisance populations since the early 1900's.  Although researchers have found some success with various pesticides, such as DDT, these chemicals are not specific to caddisflies and will kill everything in the water.  

Since it would not be economically feasible or socially responsible for CAP to introduce harmful chemicals into the canal, an alternative control is needed.  For over 10 years, CAP has invested significant time, labor, and financial resources into researching control mechanisms that will help to lessen the caddisfly impact to our neighbors.  Unfortunately, our findings are no different than what scientists have concluded for the past 100 years; there is no effective, responsible method to significantly reduce or eliminate caddisfly populations. 

Fish into Canal

Despite the unfavorable results, our investigations revealed that channel catfish will eat caddisfly larvae in the canal.   We know that the fish won't eliminate the caddisflies, but they could slightly reduce the population and possibly provide some relief.  Therefore, since 2011, CAP has stocked channel catfish into various locations in the canal to eat caddisflies.  Although results are mixed, residents generally report that conditions have improved since the catfish stockings began.  Catfish are stocked in early spring (Feb-Mar) and late summer each year (Aug-Sep).


What You Can Do

Although the CAP is a man-made canal, please remember that we deliver untreated Colorado River water to our customers.  Anything that can be found in the Colorado River, including caddisflies, will also be in the CAP canal.

If you are considering purchasing a home near the canal, please talk with potential neighbors to determine if caddisflies are an issue in that particular neighborhood.  Caddisflies typically do not venture very far from the canal, so residents that back directly to the canal see the biggest impacts. 

If you already own a home near the canal, please understand that caddisflies have been part of the CAP since it was completed in 1993, long before most homes were constructed adjacent to the canal.  Different environmental factors will cause population densities to fluctuate, but there is currently no mechanism that will eliminate caddisflies from the CAP.  Although we continue to look into alternative control methods, caddisflies and other insects will always be in the canal.

We understand your frustrations when caddisflies are swarming; below are a few suggestions to help reduce their impact near your home:

  • Keep backyard lights at a low level and limit yard floodlights
  • Replace white light bulbs with yellow “bug” lights 
  • Request that white streetlights in your neighborhood be replaced with yellow 
  • Reduce the amount of vegetation in your yard and surrounding your property
  • Bug zappers may attract caddisflies away from "sitting areas", but may also attract more caddisflies to your yard 
  • Use an insect fogger for temporary relief (caddisflies will likely return in a day or less)


For more information, contact Scott Bryan, Senior Biologist at 623-869-2474 or sbryan@cap-az.com.