Is it a termite swarmer or a flying ant?

Waist: ants have a narrow, wasp-like waist; termites have a broad waist with no pinch (Penn State). Antennae: ants' are L-shaped or elbowed; termites' are straight (Penn State). Wings: termite wings are nearly twice the body length and all four are the same size; ant wings are about body length with the front pair longer than the back (Penn State). The wings are also the evidence they leave behind. Termite swarmers shed theirs after the flight, so piles of identical clear wings on a windowsill point to termites.

Both swarm on Long Island in spring. Termite swarmers emerging inside the house mean an established colony under or in the structure, and Cornell IPM notes that winged termites appearing suggests the colony has been present for a few years. Flying ants indoors in late winter or early spring are often carpenter ant swarmers, which means a carpenter ant colony is nesting in damp wood somewhere in the house. Neither is good news, but termites are the one that needs an inspection this week.

Eastern subterranean termites swarm here from February through June, usually on a warm, humid day after rain. Carpenter ant swarmers come out around the same time. The housing stock in Nassau and Suffolk, mostly 60 to 70 years old with original sills and foundations, is exactly the age where both problems show up, so the question is worth ten seconds of looking closely.