Aquatic Moths (Lepidoptera)

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Aquatic Moth Larva
Aquatic Moth
Aquatic Moth

There is some confusion in some fly fishing circles in the difference between a Caddis Fly and an Aquatic Moth.  Some will even tell you there is no difference.  Others may say to you that there is a great Caddis hatch going on and in fact it is an Aquatic Moth emergence happening instead.  This confusion is understandable in that there is some resemblance between the two bugs at first glance.  Secondly Aquatic Moths prefer the comforts on the evening over that of daytime. So Aquatic Moths can make themselves scarce during the daytime hours.  Out of sight out of mind so to speak. 

There are a few other similarities between the two aquatic bugs other than just the visual.  Both Caddis and Aquatic Moths go through a complete metamorphosis, will build or spin cocoons or tubes, and both will pupate inside these shelters until they emerge.  This is where the difference ends.  Unlike the Caddis who must swim to the surface to emerge from the meniscus to fly away, an Aquatic Moth instead crawls to the river’s shore and crawls onto the shore to find a quiet place to dry it’s wings before flight.

There are at least 11,000 species of Aquatic Moths in 75 families in America alone.  As larva the Aquatic Moth will be in the river for at least a year and some species will be in the river for over three years.  During this time they will feed on plant material and will sometimes burrow into plants and will go through their metamorphosis there.  As adults they become pollinators helping to pollinate the riparian zone along the river as well as farmers’ fields.  Aquatic Moth adults like caddis, depending on the species, can live up to or beyond three weeks. At the end of this time they will mate and return to the river to lay their eggs.