Sowbugs

Sowbugs are not quite as prolific or as important as scuds (Amphipoda), but in certain waters they are more common and serve the same role.

They should not be imitated with the same patterns because they are much more wide and tend to sprawl their legs to the side instead of tucking them neatly under the body. They crawl around instead of swimming, so they are probably best imitated with a dead-drift (Dead-drift: The manner in which a fly drifts on the water when not moving by itself or by the influence of a line. Trout often prefer dead-drifting prey and imitating the dead-drift in tricky currents is a major challenge of fly fishing.).

They produce new broods once every two months, allowing them to populate a stream very quickly if enough food is there to support them.

This order also includes popular terrestrial (Terrestrial: Insects which live on land and are fed on by trout only when they incidentally fall into the water are known as "terrestrials" to fly anglers, and they're very important in late summer.) species commonly known as pillbugs or rolly polies. They aren't known to be relevant to fly fishermen.