Yesterday while taking the puppy out for her hourly bathroom break, I happened to notice a few swarms of insects crawling among the grass on the lawn. Closer inspection revealed them to be ants. They were reasonably contained to a small area, perhaps a foot square, for each swarm, and there were at least three or four that I noticed. They seemed to be mixed individuals, half small yellow-orange ones, and half larger reddish ones with wings. Sprinkled among them were a number of small black ones with wings.
It was the makings of a reproductive flight, and the participants are most likely of the genus Acanthomyops*. Late in the summer, on a warm, humid day, often just after a rain, these ant colonies send forth their reproductive individuals to fly, mate, and establish new colonies. The little yellow individuals are workers. They won’t be going anywhere; once all the excitement is over they’ll return to the nest and get back to business. The larger ones, though, with the big clear wings, are the new queens, and the little winged black guys are the males.
*Myrmecos comments to suggest the ants are Lasius claviger, which used to be Acanthomyops but scientific evidence showed that the species actually belonged to the closely related sister species Lasius.
They have evolved this strategy of all swarming at once for two primary reasons. The first is that if everyone comes out at once it makes it a heck of a lot easier to find a mate. Just within our little lawn there were several colonies producing reproductives that afternoon. The other reason is the whole safety in numbers premise – if everyone comes out at once, it’s impossible for predators to get everyone, so some individuals will survive to start a new colony. These swarms are sure an impressive and intriguing sight, it’s easy to sit for a while and watch them all crawling up and around and over.
Curiously, when I was looking up on BugGuide.net for more info on the genus (they don’t offer much, unfortunately), I discovered this photo of the same sort of Acanthomyops ant swarm, which was also taken yesterday. The photo was from Connecticut, which presumably had shared similar weather patterns to us here. I wonder just how many colonies were swarming yesterday afternoon?
The common name for ants of this genus is Citronella Ants, for the smell they emit when disturbed or crushed. I didn’t know this when I was looking for them, so didn’t check, but wasn’t likely to stick my hand in there anyway. They don’t have the formic acid defense that the most common household ants we encounter do, but I didn’t know that at the time. Another name they’re known by is Foundation Ants, for their habit of nesting in the loose soil that frequently surrounds the foundation of suburban houses. Unlike carpenter ants, however, they are harmless and don’t do any damage to the house, nor do they tend to forage inside.
The queens head for tall objects sticking up from the ground, such as twigs or blades of grass, from which they take off on their flight in search of a mate. Once they’ve found a male and mated, they’ll drop to the ground and look for a suitable, uninhabited location to start a new nest. The soft soil around foundations is easy for the young queens to dig in, which is why it’s so often favoured. Once the queen finds a spot she’ll drop her wings and start excavating her new home. It’s a lot of work, and will take her a while to establish. Many nests never make it past this stage.
Some species of ant, including Acanthomyops latipes (I don’t know if these are that species, or a different species of Acanthomyops), will avoid having to go through all that work by instead searching out a colony of the closely related genus Lasius. She’ll invade the colony, kill the Lasius queen, and take over control of the existing workers while she breeds a new colony of her own offspring. This behaviour is called temporary social parasitism. In fact, because of this close relationship between these two genera (as well as other reasons), Acanthomyops is sometimes considered a subgenus of Lasius, rather than a separate genus in its own right.
This little male looks tiny next to the large queens. The males, unlike the queens, will retain their wings till death, but that’s not all that far away. The male’s sole purpose appears simply to mate with new queens, after which he dies. While queens may be produced by young colonies, males are apparently only produced from older, mature colonies. A colony may last for many, many years, depending on the species. A queen will live for several years herself (up to 15 years depending on the species), but for older colonies it may not be the original queen present; rather, she may have died and been replaced by a daughter.
Not sure what this worker is doing. In fact, I’m not sure why the workers were out amid the swarm of winged reproductives period. I didn’t spend a lot of time watching them, because I had a rambunctious puppy at the end of the leash who didn’t have the same appreciation for such phenomena. I put her in her crate so I could take a number of photos of the colony, but couldn’t leave her there long. When I returned to the area this afternoon they were all gone, the area was empty. It’s amazing how fleeting it is, and you really need to be in the right place at the right time to notice it. Presumably a number of those queens I saw yesterday are now off starting a new nest of their own.
seabrookeleckie.com 
Great shots. This looks like Lasius claviger to me. (used to be Acanthomyops, but the name changed recently).
If you get a chance to smell them, do it. They have a lovely aroma.
Isn’t that interesting about the timing of the swarms? It would be great to document this over a large region and see if there is correlation. Do swarms occur more than once in a year?
Thanks, myrmecos – hard to keep abreast of all those name changes and splits/lumps that happen. I got the name from BugGuide.net, so looks like they need to update.
I was thinking that, too, Huckleberry. I get the impression from what I read that they only occur once a year.
The French word for ant is “fourmi” , as in formic acid, so I had assumed that formic acid was a basic component of all ants. (Perhaps the Citronella Ants are full of antacid? )