Order Trichoptera (Caddisflies)

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If you ask a fly fisherman about their go to flies, odds are the list they rattle off is going to include the many varieties of caddisfly patterns. The most popular pattern, the elk hair caddis was created by renowned fly fisherman Al Toth in 1957, and it has been one of the most commonly fished flies ever since. As I write this, I have three different caddis patterns in my personal fly box. So, what is this insect that fly fisherman spend so many hours trying to imitate with pieces of hair, string, and glue.

The Famous Elk Hair Caddis Pattern

Caddisflies are part of the order Trichoptera, the seventh largest insect order, composed of 45 families represented by over 16,000 species globally with 1,887 of those in North America. Caddisflies are in the supra-order Holometabola, the clade of insects that undergo complete metamorphism. Complete metamorphism means that an insect undergoes major changes through four distinct phases of development, these phases are egg, larva, pupa, and adult. Throughout three of these four stages, egg through pupa, caddisflies are aquatic, with their adult form being terrestrial. 

Caddisflies lay their eggs on the water at streams, ponds, and lakes in a gelatinous matrix. once the eggs hatch, the larvae move to the bottom of the body of water and begins to construct a case or cocoon out of particulates on the bed glued together with silk produced in the larvae's mouth. The case serves as camouflage, physical protection, and as an aid in respiration by funneling oxygenated water across the body of the larva. The materials used for constructing the case is influenced by the habitat the larvae is in. In slow moving water and the shallows of lakes and ponds the case gets made out of organic detritus, in fast currents the cases are made from sand and rock fragments, and in strong currents the finished case is fixed to larger rocks. While the currents determines the material of the case, the substrate of the body of water or stream determines the shape. In soft sediments larval cases are wide and flat and is sandy substrate the cases are cylindrical. This larval stage can last from months to years and typically the larvae go through five larval instars. An instar is a specific stage within larval development where the larvae molts and grows in size while remaining a larva. Once the larval stage is complete the caddisfly enters the pupal stage. After the last instar, the caddisfly pupates within the case where is develops into the adult form, this adult form will emerge from the case and travel up to the top of the body of water where the exoskeleton will go through sclerotization which is the process of proteins and chitin in the exoskeleton crosslinking and hardening, during this time the wing will dry and the caddisfly will fly away. The adults are are medium-sized insects with membranous, hairy wings that rest on the back of the insect when at rest. Adults have chewing mouthparts but do not feed, they reproduce and then die.


Caddisfly Life Cycle 

 Caddisflies fill a variety of niches in their habitats. The most common are as scrapers, detritovores, herbivories, filterers, and predators. The forage of choice for a majority of species are periphyton, which is a collective term for microscopic algae, bacteria, and fungi that grows on the substrate of rivers and streams. In their habitats they serve as important indicators of a healthy aquatic ecosystems as they are considered sensitive to environmental stressors. Caddisflies also serve as an important food source for fish and other aquatic species, particularly trout and salmon.


Adult Caddisfly

References

https://awwblog.auburn.edu/2023/01/19/caddisflies-and-friends/

https://www.maine.gov/dep/water/monitoring/biomonitoring/glossary.htm#periphyton

https://www.maine.gov/dep/water/monitoring/biomonitoring/sampling/bugs/caddisflies.html#:~:text=Caddisflies%20build%20an%20underwater%20cocoon,of%20these%20generations%20per%20year.

https://www.macroinvertebrates.org/taxa-info/trichoptera-larva

https://fieldguide.mt.gov/speciesDetail.aspx?elcode=IITRI18030

https://news.orvis.com/fly-fishing/Remembering-Al-Troth

https://www.uky.edu/Ag/CritterFiles/casefile/insects/caddisflies/caddisflies.htm







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