By Dr. Jennifer Biederman

As summer begins to wind down, July, August and early September bring a special treat for fly anglers in Minnesota: the trico hatch. Tricos, short for Tricorythodes mayflies, are a small-bodied but super important part of many trout streams’ ecosystems, and they offer some of the best dry fly fishing opportunities of the season.

The Natural History of Tricos

Tricos are a genus of mayflies that are particularly small, often ranging from size 20 to 24, making them one of the smallest flies that anglers use. They are part of the Ephemerellidae family and are known for their three tails and distinct black-and-white coloring in their spinner phase. These mayflies have a relatively short life cycle, with adults living only a few hours to a day, but they are incredibly prolific during their hatching period.

The life cycle of tricos begins with eggs being laid in the water, where they develop into nymphs. Trico nymphs are known for their affinity for slower-moving water with a silty or muddy bottom. They are excellent swimmers and spend most of their life cycle in this nymphal stage, which lasts about a year. When they are ready to emerge as adults, they swim to the surface and shed their nymphal shuck, transforming into duns, which soon molt into spinners.

The most exciting part of their life cycle for fly fishers is the spinner fall, which typically occurs in the early morning hours. During this time, trico spinners fall to the water’s surface to mate and die, creating a perfect opportunity for trout to feed on these vulnerable insects.

Tricos in Their Habitat

Tricos thrive in cold, clear streams and rivers with ample vegetation, which provides the necessary nutrients and habitat for their development. These insects are commonly found in limestone streams and spring creeks, where water conditions remain relatively stable throughout the year. The hatch usually begins in mid-summer and can last through early fall, depending on the region and weather conditions.

Fly Fishing with Tricos

Late summer mornings, when trico hatches are at their peak, offer an incredible fly fishing experience. Trout can often be seen sipping these tiny insects off the water’s surface, and having the right trico pattern in your fly box can make all the difference. Due to their small size, fishing with tricos requires a delicate presentation and often lighter tippets, such as 6x or 7x, to avoid spooking wary trout.

Anglers should be prepared for the challenge of matching the hatch and dealing with the often finicky nature of trout during a trico spinner fall. Patience and precision are key, as the best fishing can happen during brief windows of activity when the trout are actively feeding. In conclusion, tricos are a late summer staple in the fly fishing world, offering a unique and rewarding challenge. Understanding their life cycle and habitat can greatly improve your chances of success on the water, and there’s nothing quite like landing a trout on a perfectly presented trico fly.

What’s a macro and what’s it have to do with trout angling and conservation? Macros are on the trout menu for pretty much every meal. Macro means big and macroinvertebrates, or “macros,” are animals without a backbone, that are big enough to be seen by the human eye. They can be aquatic or land based, however aquatic insects make up the majority of a trout’s diet. They are also, of course, the inspiration for the flies we tie and use to catch trout. Learn about a new macro each month and how you can create your own to take with you on your next fishing trip!