The Lightning Bug is pure flash. The body is wrapped tinsel or pearlescent Flashabou under a thin ribbing, topped with a bead and usually a peacock or dark thorax. There's no mayfly or caddis it's copying - it reads as a generic flashy nymph, which is exactly the point. When trout aren't keyed on a hatch, the shine gets them to commit.
Tie it in sizes 14-20. Silver is the all-around default and shines in clear water and bright light; gold runs a touch warmer and earns its keep in stained or tannic flows. Both work best when water temps sit in the 42-60F window, which covers most of the trout season outside high summer.
Fish it dead-drift like any nymph - under an indicator or as the dropper below a heavier point fly on a tight-line rig. It works as a searching pattern in normal flows: put it through riffles, runs, and the heads of pools where fish hold in the current and pick off drifting food. Use the flashier silver in clear water; drop to gold when the river carries color.