"Ant swarms" are most commonly associated with ants mating and the subsequent establishment of new colonies. However, non-native pavement ants (Tetramorium caespitum) may also swarm for a more nefarious purpose: to conduct full-blown, no-holds-barred ant wars.
For Love and Food
The vast majority of the individuals found in ant colonies in Ohio are wingless sterile females; the "workers." Only queens can lay eggs but once they start their colonies, they never leave.
Periodically, fertile winged ants, both males, and females are produced. These are called "alates" and the new queens will establish new colonies. The alates fly off to mate and their departure is accompanied by swarms of workers to see them off. Pavement ants generally produce mating swarms in the late spring to early summer.
Pavement ants were introduced to the U.S. from Europe over 100 years ago. They are sometimes mistakenly considered to be natives owing to their general establishment throughout a wide swath of North America. I've referred to them as a single species, Tetramorium caespitum. However, their exact taxonomy remains tangled. Most ant resources refer to pavement ants as a species complex.
Their habit of locating their underground colonies beside or beneath sidewalks gives rise to their common name. Mounds of loose soil particles emerging from sidewalk cracks or expansion joints are often the work of pavement ants.
The ants scavenge for a wide variety of food including tiny pieces of bread crumbs and other detritus in our kitchens, live and dead insects, honeydew from aphids, grease, etc. The worker's ability to range widely to locate food and find their way unerringly back to their colonies while laying down a chemical trail for their sisters is phenomenal.
As with other hymenopteran stinging insects (e.g. wasps and bees), pavement ants have stingers that are actually modified ovipositors (ovi = eggs). Their stingers are too small to penetrate our skin; reports of skin rashes are generally associated with their bites. However, the pavement ant's stingers do play an important role in laying down a chemical trail. Their stingers are broadened at the tip which acts a bit like a spatula in depositing trailing pheromone.
Springtime is also battle time for the pugnacious pavement ants. Instead of "make love, not war," they make love and war. Look closely at pavement ant swarms and if you don't see ants with wings, love is not in the air. You're seeing a full-blown ant war.
Pavement ants are very protective of their feeding territory and intolerant of nearby colonies. They are well-known for their bare-tarsal brawls. Battles may occur as a massive, swirling clash of six-legged combatants or as a serious of smaller pitched skirmishes with constantly shifting battle lines.
A close examination of the melee will reveal ants locked mandible-to-mandible in ruthless combat. Battlefield injuries range from crushed abdomens to dismemberment. Ant wars provide questionable antertainment and I've often wondered if the Romans got their gladiatorial ideas by watching pavement ants.
Some ant wars arise as territorial disputes resulting from scavenging workers based in adjacent colonies continually bumping into each other. Others occur as colonies try to expand their territories with two colonies "planting their ant flags" in each other's territories. These disputes are settled on a neutral battlefield between the two colonies, presumably with ant-drums and bugles blowing.
The most brutal battles happen when one colony decides to raid a nearby colony. These fights are bloody affairs with macerated bodies quickly piling up.
Colony raids occur right on top of the colony that's having a bad ant day. The defending colony quickly pours all available combatants into the fray. Even winged alates may be seen mixing it up with the opposing force. Although alates are much larger than their colony kin, they are built for love, not war. They do not fare well with their farewell marked by disassembly.
Most ant wars are settled quickly. The engagements are over after a few hours with nothing left on the battlefield to mark the epic confrontation. That's because the spoils of war for ants include the bodies of the defeated which are trundled off to feed the victor's colony … a different twist on carry-out.