Introduction & Overview
Aphaenogaster occidentalis were the first species of ants I started keeping. Back then, I didn't have an amazing community to rely on, and I made a lot of mistakes keeping the colony. However, the colony was both generous and patient, and it managed to survive and proliferate. Because of this, I definitely recommend these ants as a beginner's species!
A. occidentalis are not very fond of heat in my experience. They tend to shy away from heat sources and prefer much cooler areas. Colonies are usually found nesting under rocks or slabs of concrete, where the dirt is nice and cool. Colonies of A. occidentalis keep their brood close to the surface, and the entire colony can be found within a few inches from the surface of the soil.
While Aphaenogaster are usually more rare in western North America, A. occidentalis thrive in suburban areas, including Silicon Valley. My own yard is full of colonies of A. occidentalis.
I would call these ants semi-nomadic because of their ability to move wherever suits them the best. Colonies may stay in one place for a while, then suddenly decide to move if they find a nice hollow piece of wood.
In contrast to other species of ants, Aphaenogaster prefer solid foods which they can bring back to the nest to feed directly to the brood and their queen. They do not have social stomachs, which means they are unable to regurgitate the food that they have consumed. They are less likely to accept liquid sugar as food, but they readily take foods such as a piece of a sweet fruit or organic granulated sugar.
Because Aphaenogaster don't have social stomachs, workers will lay haploid eggs to be fed to the queens. If the workers lay too many eggs, not all of them will be eaten, and the haploid eggs will eventually develop into males. This situation usually occurs if the colony is fed a lot of food, but you would also have to keep in mind that these males will also increase the food intake of the colony.
Aphaenogaster occidentalis are by far the most common Aphaenogaster that can be found in the areas they reside in. They are extremely numerous especially in suburban areas, and the location of capture should be the first sign to ID A. occidentalis. At first glance, they may be mistaken for larger Tetramorium workers. They can be distinguished from Tetramorium workers by their head, which is much longer and more oval in shape.
Another thing to look out for is the location of capture of the ants. If you find a colony, its location can tell a lot about what genus the ants are part of. Aphaenogaster prefer moister conditions away from too much heat, compared to similar Pheidole and Tetramorium which nest in warmer areas. Aphaenogaster also generally have smaller nests, with the majority of the brood and queens very close to the surface of the ground.
A. occidentalis are fairly easy to distinguish from other species of Aphaenogaster because most other species of Aphaenogaster that are found in the same area are more skinny and have longer legs. A. occidentalis are also either dark brown or bicolor, with darker colored gasters. Under very bright light, the ants may also have a reddish tint.
Aphaenogaster occidentalis queens are 8-9mm in length.
A. occidentalis are fully claustral and do not need to eat during their founding stage. However, from my experience, they are more open to the occasional snack compared to other ants and can be given a dead fruit fly to eat from time to time. During the founding stage, the ants should be kept out of direct light and vibration and left alone so that the queen does not get stressed and eat her brood.
A. occidentalis will lay eggs even if they are not fertile, and some of them will even develop into males. The only way to know for sure whether they are actually fertile is once they get workers. However, fertile queens will usually have larger and more successful brood piles, as only 10% of haploid eggs actually end up developing.
They do not need to dig in order to survive and do find without getting any substrate. If the ants are given substrate, like sand, they will only use it to cover up cracks and ruin visibility of the colony.
Colonies are highly polygynous and are usually more successful with multiple queens. However, I would hold off on attempting to combine colonies until they begin to develop workers.
The worst mistake that could occur caring for these ants is checking on them too much. Queens can get stressed out and it is important to give them time to accustom themselves to their environment.
high, gradient, offer multiple nests if possible
If Aphaenogaster occidentalis are uncomfortable with the heat that has been provided, in my experience, they will crowd very close to the cotton to try and escape the heat. They also prefer higher humidity, and the brood is kept very close to the cotton to keep it hydrated when the ants are in a test tube setup.
Time to first workers
4-5 weeks unheated
During the founding stage, Aphaenogaster are not especially picky, but they should be given at least 24 hours to settle down into their new home. Signs that the queen does not enjoy her new home could include running around in circles and pulling at the test tube cotton.
Tubs and tubes
When setting up for Aphaenogaster occidentalis, the two most important things to keep in my are whether they can bring their food into their nest and whether their nest is humid enough. They prefer very wet environments over dry environments, and in my experience, they will often take bits of cotton or mold and stack it up in the middle of the test tube in order to capture more humidity and retain a moist environment for nesting. When making a tube and tube setup, I would make sure to reduce the size of the test tube entrance with some substrate or other materials to help retain the humidity for their nest.
If the ants start stacking up trash and cotton in the middle of their test tube, it becomes difficult for them to drag food into their nest. Aphaenogaster feed their brood most successfully by placing the larvae directly onto the protein. If they can not drag the food they are provided into their nest, the ants will have a difficult time feeding their larvae. Food should also be cut down into smaller pieces so that the ants can fit it down into their nest.
I would recommend organic granulated sugar as the number one food source for Aphaenogaster. In my opinion, it is the best food for them because they will not bury it and it is much easier for them to bring it back into their nest. However, I would also only feed a few pieces of granulated sugar at once, because once the ants bring them back into their nest, the sugar will end up melting inside the tube and causing a mess, possibly drowning a few ants.
I would feed around every other day early on in the colony development. They are very fast growers when provided with enough protein. Aphaenogaster are not picky eaters and will take anything from pieces of chicken to small fruit flies. I recommend fruit flies as the number one food source for them when the colony is smaller, because they can be used the gage how fast the ants consume their food.
Aphaenogaster are scavengers, and thus, can eat desiccated (dehydrated) insects as well. If they haven't finished the cricket you've fed them, there isn't a need to add more food until they are done eating. Most of the time, die-offs are caused by poison in the food, including different types of pesticides. I would only feed protein and fruits that I know the source of. Wild insects can have pesticides in them, and so can store-bought fruits. I very much recommend insects bought at pet shops or raised in a culture instead of other types.
In the past, my A. occidentalis have done well in formicaria with high humidities and gradients, such as TarheelAnts Mini Hearths and TarheelAnts Fortresses. These formicaria have more room for the ants to grow compared to test tube or tub and tubes setups. They also retain humidity better than test tubes and are perfect for Aphaenogaster occidentalis.
Once the ants have moved into larger formicaria, you can try heating a corner of the nest, away from the source of humidity to see if it is to their liking. While they don't like a lot of heat, they may still adjust their brood according to the gradient, and this will also give you a better idea of what temperatures your ants are used to.
Larger Aphaenogaster occidentalis colonies are very active foragers and will eat a lot. I would expect to see alate brood in the nests as early as 20-30 workers, and even more once they reach the hundreds. It is possible that Aphaenogaster occidentalis may mate inside of their nests and spread by budding, so this is another thing to keep in mind as the colony gets larger. Cleaner crews usually aren't necessary, because these ants can finish pretty much everything that's given to them, so long as they can bring it into their nests and feed it to their brood.
Larger colonies are also more sensitive to lack of food, and I would make sure to feed enough to them so that they can continue to produce brood and maintain their colony size. At a certain point, they will only grow as much as they are fed, and this can be used to control the population of ants inside the colony.
A. occidentalis are often mistaken for Tetramorium immigrans in urban settings
If anyone else has anything to add to my caresheet, please let me know! I'm also always looking for reviewers and questions to help out and make this a better caresheet. I hope everyone who reads this learns more about how to maintain a colony 😀