Rain Puts Ants – And Ant Fanatics – Into a Tizzy

Most of the time it doesn’t look like much is going on in the Sonoran desert during the day.


Of course, looks are deceiving, because there is often a lot going on that is subtle.

After a rain like we had this weekend, however, life comes bursting out.

We went for a hike at South Mountain Park on Sunday morning. Rain had fallen in the night, and as you can tell from these photographs, it was still cloudy. It was also extremely humid.



It is impossible to capture the level of activity in photographs, but ants were just streaming out of their nests. These are shiny black Messor pergandei.

Rain stimulates activity for at least two reasons.


First of all, the ants are scurrying to collect seeds.


Some desert plants release their seeds in response to rain. Also, the rain knocks down seeds that are higher up in trees and shrubs. That means there is a flush of new seeds to collect after a storm.

Most of you probably already know the second reason ants are hyper-active after a summer rain.


See if you can spot the reason in these photographs of a Pogonomyrmex rugosus nest entrance.

p-rugosus-princess-2.JPG p-rugosus-princess-3.JPG p-rugosus-princess-4.JPG p-rugosus-princess-5.JPG


Did you spot the princess (alate)?

She went back inside this time, but I bet later in the afternoon the alates from this nest were swarming.

Wish I had all day to watch them and a HD video camera. Maybe someday soon…

Are the ants swarming where you live?


Harvester Ant Mounds II

While observing the Messor Pogonomyrmex rugosus nest last week, I noticed one ant working on a seedling that was in a patch of other small plants to one side of the mound. (These are mostly Pectocarya – combseed).


The worker ant seemed to be using its mandibles on the base of the plant.


Of course, Messor worker ants clear plants from the area around the mound.


It makes sense to prevent plants from shading the mound too much. Ants are known to regulate the temperature within the nest via mound architecture.


Wish I had more time to spend observing this activity.

Do you have any ideas what this ant is doing?

Harvester Ant Nest Midden

During a quick hike through South Mountain Park in Phoenix, Arizona yesterday, I spotted a Messor Pogonomyrmex rugosus harvester ant mound.


The refuse or midden pile was covered with a fluffy material.


The ants apparently have been collecting the seeds of this plant, and discarding the seed coats.


It is a common plant in the Sonoran desert. Do you know what it is?


The plant is a food source to a range of insects as well as Messor harvester ants, including more than 20 species of bees.


It is the common creosote bush, Larrea tridentata.

The midden piles of harvester ants, as with many other types of ants, are known to improve the nutrient levels in the soil in the immediate area.

Tomorrow I will post more about Messor harvester ants.

Hum, now that I think about it, I wonder if “midden piles” is redundant, because midden is a trash heap. Anyone out there help me out on this?

Edit:  Thanks to Alex Wild for pointing out that these ants were Pogonomyrmex rugosus, not Messor.

Edit: Here’s a photo of Pogonomyrmex rugosus.

For more information, try:

Desert Harvester Ant, Messor pergandei

Dale Ward has some videos of Messor pergandei in action, as well as more information

More about cresote bush and the Zygophyllaceae (caltrop family) at the Arizona-Sonora Desert Museum