The Ants of Harvey Mudd: Which Ones are You Seeing?

I’m sure you see ants in your daily life, climbing on your ceiling, in parks or other outdoor spaces, and just around where you live. I mean ants are everywhere. Have you ever wondered how to tell which ant you're dealing with and how that ant interacts with the Southern California ecosystem surrounding Harvey Mudd?

If so you’re in the right place! First up, and my personal favorite, are harvester ants or Pogonomyrmex californicus. They are pretty big for ants (worker ants are up to 10mm!) and are native to Southern California. They are also the easiest ants to spot because they are bright red. A picture of them is below.

Harvester ant presumably standing or foraging, Jonathan Coffin

You’ll see these ants in sunny exposed areas, especially in the natural chaparral in southern California. You'll see them in the interior more than the sides of an exposed area because they thrive without irrigation (they get water from seeds). They’re my favorite because of how hardy they are and how unique each colony is. The variation in activity as colonies become bigger and older makes them a great species to study.

Next are some of the smallest ants on this campus, Forelius, which are only around 1.5-2.5mm long! These species are also extremely hard to tell apart, partially because of how small they are and that there are multiple different species. In fact when we are reviewing footage of the ants we study (we film harvester ant colonies throughout the day) we can barely see them. Forelius pruinosis makes large colonies in arid areas and it's not uncommon to see them around campus in sunny concrete areas (at least that's where I’ve seen them). When you kill them they also release a sweet tapinoma smell which (I’ve heard) smells like blue cheese.

We can't talk about ants in SoCal without talking about Argentine ants (Linepithema humile). They are an invasive species that's new on the block (they’ve only been around Southern California since the 80’s) and they’ve been eradicating colony after colony of any other species on this list (along with others all around the world). They are also the species that you are most likely to see at Harvey Mudd and around Claremont. You're most likely to see them anywhere with sprinklers or water (so everywhere) and inside the dorms / residential areas. If you have an “ant highway” it's definitely Argentine.

A video taken by my prof inside her house (video credits: Matina Donaldson-Matasci).

Argentine ants are small, only about 3.175mm, but they live in huge groups or supercolonies that can reach sizes of up to 1 million ants. Argentine ants are the ants you see trailing wherever you live; by trailing I mean a large group of ants moving in a very tight knit group from point a to point b.

Finally the last species I'll mention is Dorymyrmex insanus; these look shockingly like Argentine ants, so much so that the best way to distinguish between the species is by their behavior. If you see ants trailing they are probably Argentine. Another way you can tell is by looking at their shadows. Dorymermex have longer legs which means they also have longer shadows. I haven’t seen any around campus but Dorymyrmex does well in hot, exposed environments like Claremont, so the combined campuses of the 5C’s are a good habitat for them. A fun fact about Dorymermex insanus is that they tend to eat sugary liquids; Argentine and Forelius ants do as well.

Further reading

1. Harvester Ant - an overview | sciencedirect topics. (n.d.-a). https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/harvester-ant
2. Ant, Forelius sp.. (n.d.). https://nathistoc.bio.uci.edu/hymenopt/Forelius/index.html
3. Argentine ant, Linepithema Humile. Urban and Structural Entomology Program at Texas A&M University. (n.d.). https://urbanentomology.tamu.edu/urban-pests/ants/argentine/
4. Dan Suiter, B. T. F. (2025, September 3). Argentine ants. CAES Field Report. https://fieldreport.caes.uga.edu/publications/C926/argentine-ants/
5. Dorymyrmex insanus (Buckley). Dorymyrmex insanus. (n.d.). https://www.navajonature.org/ants/dolichoderinae/dorymyrmex-insanus.html
6. Harvester Ant - Torrey Pines State Natural Reserve ®. (n.d.). https://torreypine.org/nature-center/insects-spiders/samples/harvester-ant/

Media Credits

1. Photo by Jonathan Coffin: https://flic.kr/p/TSnGYD
2. Video by Matina Donaldson-Matasci