Forelius pruinosus

Forelius pruinosus is a small (1-2 mm) ant that is very common in the Phoenix area. You probably see them running running in columns along the sidewalks and streets as well as the in the desert. They love warm weather - they are much more commonly seen in the summer months, even on days that are so warm that few other ants are active.

They eat small insects as well as any sweet liquids that they can find. They are commonly found at extrafloral nectaries on cactus and other plants, and it is also common to find a stream of Forelius pruinosus running up the bark of paloverde trees.

If you crush one of these ants, you will note a sort of fruity odor. This is characteristic of many ants of the subfamily Dolicherinae.

The overall impression one gets of Forelius is that of large numbers and a frantic pace. The individual ants in the columns typically run by at high speed.

As always, click on the images below to get larger versions.


Here's a F. pruinosus nest with ruler for scale.

Closer view of a nest entrance.

View of F. pruinosus on a centimeter ruler. You can see that they are not very large.

A column of Forelius pruinosus running along a sidewalk at night.

A closer view of the same stream of ants. If you look closely, you can see that some of the ants have been stepped on by passers-by. The column just keeps going...

Photos of a different Forelius column, in the same Phoenix city park. The blade of grass provides a good measure of the scale - these ants are quite small.

Forelius pruinosus foraging on nectar from a saguaro blossom. There was a long column of ants climbing the side of the sagurao, sadly, they were running to fasst for me to get a good photo.

Here are some views of Forelius at the nest. Again, note the large numbers of ants in these pictures.

Late every summer, a Forelius nest in our front yard starts sending out columns of ants. I'm not sure if it is the same nest every year.

They run along in dense streams, at an incredible clip.

Often, the stream of ants will lead to a bush.

Here is one of the Forelius carrying what looks like a nymphal Homopteran (they feed on plant juices) back to the nest.

A returning ant with a Homopteran passes an ant that is on her way out.

The ant in the left of the photo has a whitefly that she has caught.

A better view of another ant with a whitefly. They were catching the flies on a very well-watered brittlebush.

Microscopic view of an adult white fly.

Since they are small and their integument is fairly transparent, it is a blast to look at Forelius under the microscope. Here is a shot of a Forelius abdomen.