First of all, "swarming" is a term often used by entomologists to describe forming and departing of a mass of individuals from an insect colony. In addition to ants and termites, bees, wasps and yellowjackets may swarm. If the insects are ants or termites, there will be a number of winged individuals present in the mass of insects. These individuals are the reproductive queens and kings of the colony that will disperse to establish a new insect colony. Capture a couple of these winged individuals in the swarm and look for these three distinctive differences between termites and ants. See FAQ #813: "How can I tell the difference between flying ants and termites?"

In the area of the swarm, look for evidence of insect-damaged wood. Most ant species do not damage wood, but a few species prefer to nest in soft wood that has been damaged by water or is in the process of breaking down or rotting. Ants do not eat wood but will chew tunnels and chambers within the wood itself, so look for signs of sawdust under the damaged wood. Most termite species also prefer soft or water-damaged wood, but some species will infest dry, undecayed wood as well. Unlike ants, termites will eat wood. Look for darkening or blistering of wooden structures and look for clay-like tubes or tunnels leading from the soil to the wooden structure. If you determine that the swarm is termites or you find evidence of termite damage to any wooden structures, it is advisable to hire a professional exterminator as soon as possible. If you determine that the swarm is ants and you find evidence of ant damage or sawdust under any wooden structure, you may want hire an exterminator.