Baetis Spinner (Rusty). One of the more prolific mayflies, the Baetis Rusty Spinner is found throughout all North American trout streams. The regularly hatch in impressive numbers and duns can be seen for extended periods on the surface before taking flight. The Baetis is also known by many fly anglers as Blue Winged Olives. This is one of our very top selling flies Mayfly imitations.