Is it a cicada killer or a hornet?

Cicada killers are among the largest wasps in North America at 1 1/8 to 1 5/8 inches, with a black body, yellow to white bands, and a dark red head and thorax (Ohio State). They nest alone in the ground, one female per burrow, in dry, sandy, thin-grassed soil, and each burrow entrance has a U-shaped mound of excavated dirt. Bald-faced hornets are about 3/4 inch, black with a white face, social, and their nest is the gray paper football hanging from a branch or an eave (Cornell IPM). Yellowjackets are smaller still, yellow and black, and nest in the ground or in wall voids in colonies of thousands.

Cicada killers look terrifying and mostly aren't. Males, the ones that dive at you, can't sting at all, and females are mild-mannered and fly away when disturbed (Ohio State). Hornets and yellowjackets are the ones that hurt people: a threatened colony attacks as a group, and crushed workers release an alarm pheromone that brings more (Cornell IPM). If you've been stung more than once at the same spot, it's not a cicada killer.

Cicada killers love the sandy, well-drained soil of the South Shore and the sand beds under pavers, pool decks, and patios all over Nassau and Suffolk, and they come back to the same yards every July because the next generation emerges from last year's burrows. Hornets and yellowjackets peak in August and September when colonies are at full size. Both are worth a call when the numbers are high, but only one of them is an emergency.