Ants, Not Gnats, Were Swarming Philadelphia Yesterday

Many people around Philadelphia reported swarms of flying insects yesterday evening. Entomology Curator Dr. Jon Gelhaus and Curatorial Assistant Isa Betancourt have the details about what exactly was going on:

L. neoniger

L. neoniger photo: Isa Betancourt

What was swarming? The swarms were ants, not gnats or flies or mosquitoes. The swarms were Lasius neoniger, a species of ant common to the area. Academy entomologists conferred with ant expert Dr. John LaPolla of Towson University to identify the species this morning. The swarming of the winged reproductive forms occurs in the fall, and this ant has been called the “Labor Day Ant” by some because it swarms noticeably around Labor Day. Gnats as a common names usually refers to small flies. These are ants, distinguished by the raised bump between the thorax and abdomen, and an elbowed antennae.

Why? They were swarming because they were mating. “I didn’t want to say it, but that’s exactly right, it’s orgy time,” Entomology Curator Jon Gelhaus told the Philadelphia Inquirer. The conditions for mating were right last night, regarding recent rains, temperatures, and the time of day (about sundown last night) for the ants to emerge from their colonies and form swarms in the air to find mates. Most of the males swarming will not mate and will likely become a meal for spiders, birds, or even other insects.

Is it going to happen again? It could. The swarms usually disappear after a day or two, but it is possible for similar swarms to happen with different species in the coming weeks.

Did Hurricane Irma cause this? No, it didn’t. The ants are local to our area and the massive hurricane did not influence the swarming that occurred last night. On on the effect of the hurricane, Gelhaus and Betancourt agree, “These are not here because of the hurricane – this is a normal annual occurrence although perhaps in larger numbers this year due to the milder winter and cooler late summer.”

What happens now? The mated females (new queens) will land, and then find a place to overwinter until next spring when they start their new colony in earnest; they will shed their wings when they land and overwinter. The males will die in a few days with their only function being to mate with a new queen.

Ants collected yesterday evening in Swann Fountain by Isa Betancourt