Crematogaster: the acrobat ants of late summer

Most ant identification takes a hand lens and a book. Crematogaster takes neither. Touch a trail, or just watch one carrying food, and the worker's rear body swings up and forward over its own back into a raised, heart-shaped point. Nothing else common in a North American garden does that. It's called the acrobat ant for exactly this reason, and once you've seen the posture once you'll never mistake the genus again.

The genus is genuinely widespread, from small dark woodland species to larger ones that nest in old stumps, under bark, or occasionally in house framing near moisture. What they share, besides the gaster trick, is a late-summer flight that most people walk past without registering, because by late August the loud, unmistakable Lasius swarms of July have already come and gone and nobody's still looking up.

Crematogaster's flights lean toward the warmer, more humid stretch of the day rather than dawn or dusk, which puts them squarely in the muggy part of a late-summer afternoon when most people are indoors with the air conditioning on. Roughly the same conditions that send a person inside are apparently what a winged Crematogaster has been waiting for.

University of Minnesota Extension lists mating swarms from July through September. Timing varies by species and location, so use that regional window as a starting point for checking local records.

The Mediterranean species Crematogaster scutellaris has actually had its flight altitude measured directly, in a drone-trap study over Italy: queens were captured 80 to 95 metres up, roughly 260 to 310 feet, right in among the other mid-height fliers in that dataset. That measurement applies to C. scutellaris at the Italian study site. It does not establish the flight altitude of US species.

A landed Crematogaster queen keeps the same tell as the worker, a gaster she can flick up over her back, though she'll often hold it lower and less dramatically than a worker mid-alarm. She's smaller than a Camponotus queen and darker and glossier than most Lasius. Get her to raise that rear segment even slightly and the identification is basically done.

Founding follows the ordinary fully claustral pattern most ants use: she seals herself away, lives off her own reserves, and doesn't need feeding until the first workers appear. If you want the fuller rundown on what fully claustral means and how to tell it from the species that need help, fully claustral or not covers that ground properly.

Late summer in the US runs several genera at once. Harvester ants and the monsoon covers the Southwest's rain-triggered flights around the same weeks, and if you're further along with a queen already in a tube, you caught a queen this week, now what is the next few days. Dealate's forecast tracks Crematogaster alongside the rest of the species active where you are, so a warm, humid, still afternoon in late August doesn't look identical to an ordinary one.

The raised, heart-shaped abdomen and July-to-September swarm window are described in University of Minnesota Extension's acrobat-ant account. That regional account does not establish one flight calendar for the entire United States. The Crematogaster scutellaris flight-altitude figures are from Giannetti, Schifani & Grasso (2025), An adhesive drone trap for the study of flight altitude preferences of winged ants, Current Zoology 71(5): zoaf002, a Mediterranean drone-trap study. The full source list behind the forecast model is set out on the methodology page.