Ants of the Week: Lasius flavus and Lasius nearcticus

The path to discovery can be encountered in many ways. Take, for example, flipping over a rock in upstate New York last week.

I knew immediately the ants were Lasius (once upon a time called Acanthomyops). I also knew the ants were not Lasius claviger because of something that was missing. Can you guess what?

If you surmised there wasn’t a citronella smell, you are correct. Lasius claviger workers are called citronella ants because of the strong odor they give off. These Lasius were relatively odor free.

Given the size and other characteristics, my guess is either Lasius flavus or Lasius nearcticus.

Lasius flavus is commonly called the “yellow meadow ant.” It is found in Europe, eastern North America, and even into Asia.

Lasius nearcticus is sometimes called the “golden cohabitant ant.” It is found in eastern North America.

According to the key to Lasius of North America found at, the two species can be distinguished by the segments of the maxillary palps. If the terminal maxillary palp segment is longer than the penultimate segment, then the ants are probably L. nearcticus.

I didn’t collect any specimens for further identification. Are there any experts out there that can tell the species from these somewhat blurry photographs?

Lasius are known to tend root aphids and mealybugs. The plump white blobs are root aphids because they have cornicles, the projections at the back of the abdomen.

The root aphids apparently had overwintered with the ants, because the day before it was snowing where I found these. Lasius move the aphids to plant roots where the aphids feed. In exchange, the ants gather honeydew from the aphids. They also are known to eat the aphids, especially in the winter.

That said, I was a little surprised to see this under the next rock I encountered:

This colony had piles of black, oval objects.

I found other similar photographs online, like this one.

Any ideas what the black ovals might be? (The answer will be posted on Friday.)

The reproductives of these two species tend to be darker brown than the workers. Here’s a video of a colony of Lasius flavus.

It would be be interesting to learn more about these two species. Have you ever seen these ants?

For more information about Lasius and aphids, try:

PONTIN, A. J. (1978), The numbers and distribution of subterranean aphids and their exploitation by the ant Lasius flavus (Fabr.). Ecological Entomology, 3: 203–207.

Joachim Offenberg. (2001). Balancing between mutualism and exploitation: the symbiotic interaction between Lasius ants and aphids. Behav Ecol Sociobiol,  49:304–310