In addition to RIO's Bubble Up May, we wanted to add a tungsten "split back" style nymph into the lineup of Mayfly nymphs. A seriously reliable trout snack— PMD nymphs are often found in a brown hue until they mature into adults in a yellow-ish fashion. That's precisely why we added a yellow bulge to the top of the thorax. Not only does it replicate the beginning stages of emergence, but it also serves as an attractive trigger for the fish. The tungsten bead allows this fly to be suspended in the mid to upper water column when dropped off a dry or as the anchor fly in a light nymph set up.