Darkwing fungus gnats are not a cause for alarm
Poverty grass and moss possibilities for a garden path
This is a neat find — a fungus gnat larvae migration. Not on a par with the eclipse maybe, but you may never see one again in your lifetime. In some years we have the exact weather conditions that favor darkwing fungus gnats. This species of gnat is tiny and innocuous. It’s larvae hatch in moist soil and eat soil fungus. (It’s not the nuisance fungus gnat associated with houseplants.) If a large number of eggs hatch near each other, the larvae aggregate and migrate en masse, forming a snake-like line crawling atop each other. The migrations are often noticed moving across a sidewalk or driveway. It’s an interesting phenomenon, that’s all. No cause for alarm. Search fungus gnats on the HGIC website.
Danthonia spicata (poverty grass) and moss are native possibilities. Neither tolerate heavy foot traffic but can make a beautiful path. Mulch would be environmentally friendly, because it decomposes and feeds the soil/plants. It also cushions soil from foot traffic compaction, which benefits everything alive in soil. A most important environmental issue is erosion control. Neither mulch nor moss work well in that capacity on a slope. Typical lawn grasses qualify as environmentally friendly in that respect. Some fine fescues, e.g. chewings or hard fescue, are mowed only about once a year. Fertilizer is minimal. For Maryland state fertilizer recommendations, search the HGIC website. Aim to use just enough to feed turf and not run off. Stepping stones cause less water run-off compared to solid paving stones.