Baetis and Callibaetis (Mayfly) Nymphs

Although different types of mayfly nymphs are present in streams, lakes and rivers, it is only those that are good swimmers – the Baetidae family – that are of particular interest to anglers outside of hatching season. The day to day habits of Baetidae nymphs in general and of two genera in particular – Baetis and Callibaetis – mean that they are food for trout throughout the year, and therefore present the opportunity to use patterns that mimic them in most stretches of more gently-flowing freshwater.

The difference between Baetis & Callibaetis

You could be forgiven for thinking that one is an abbreviation of the other, but this is not the case. The Baetidae family make up about one thousand (out of over three thousand) different species in the Mayfly order, and Baetis and Callibaetis are separate sub-groupings (or genera) of that family. The Callibaetis genus contains around 30 species. The Baetis genus has around 150 different species, commonly and collectively known as Blue Winged Olives.

Mayfly Nymph Life Cycle & Behavior

Some nymphs are carnivores, but most feed on algae and small bits of rotting vegetation; some filter tiny food particles from the water. Some species spend two years as nymphs, but an annual life cycle is most common. Baetidae nymphs are colloquially named ‘agile darters’, reflecting the fact that they swim. They are generally found in larger numbers in less fast-flowing waterways. Although they are capable swimmers they also allow themselves to drift with the current to relocate on a regular basis.

Fishing with Baetidae Nymph Patterns

Baetidae tend to hitch a ride in the current to a new stretch of the water at either sunrise or sunset, so this is when a dead drift technique can be most effective. Otherwise, a lightly weighted pattern and gentle twitches on the line will mimic the way these nymphs flick their abdomen and tails up and down to swim.