In today's fly fishing world organizing a catalog, has become more difficult. There used to be a clear cut line, there were streamers, nymphs or dry flies. You either fished on top of the water or Sub-surface. Now the division is blurred with the emergence of the Emergers. Ironically the old group of flies once called 'wet flies' make some of the best emergers around. Soft hackle flies make excellent emergers, as the collar of soft hackle gets wet it collapses around the body and looks like the nymphal shuck being shed by the emerging nymph.
When speaking of emergers, one is usually referring to mayflies. Soft hackles, pheasant tail emerger, and various floating emerger patterns are very popular. Floating patterns usually hang just in the surface film, that first six inches of water where fish slurp greedily during hatches.
Caddis pupa also are emergers, no longer larva, they emerge on buoyant gasses, to emerge as an adult. Some take their sweet time during this phase making the Emergent Sparkle Pupa, a wonderfully effective pattern.
Emergers usually are fished just below the surface, on an unweighted line. Keeping the presentation natural can be a challenge as the fly isn't usually visible. Some use an indicator to detect any unnatural drag, and where fish aren't easily spooked, this approach can be effective. Also using a dry fly as indicator can work quite well and gives the added advantage of being able to entice a few strikes as well.
No matter how you fish them, Emergers have become a staple in every discerning angler's arsenal.