Pogonomyrmex rugosus
(Black Harvester Ant)
Care Sheet

What is Pogonomyrmex rugosus?

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Pogonomyrmex rugosus is a large seed-harvesting ant from the deserts and dry grasslands of the southwestern United States and northern Mexico. You'll hear them called the Black Harvester Ant or the Rough Harvester Ant. The name rugosus is Latin for "wrinkled," which in this species is referring to their ridged sculpturing.

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Workers come in two looks: fully jet black, or an orange and black form. Either way, they're big, bold ants that build large colonies and patrol big territories in the wild. In captivity they can live almost entirely on seeds, but they grow best when you add protein too.

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They're energetic foragers, they're fun to watch hauling and processing seeds, and yes, they sting. More on that below.

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How to identify Pogonomyrmex rugosus

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Rugosus are large, heavily sculptured harvesters. Look for:

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• Size: workers ~8-9 mm, queens 12-14mm. Worker size in captivity may vary, as workers tend to be smaller when the colony is young.

• Sculpturing: coarse wrinkles (rugae) across the head and thorax, which gives them a rough, matte look up close.

• A psammophore: a beard of long hairs under the head, used to carry sand and soil when digging. Most Pogonomyrmex have this.

• Color: solid black, or orange and black, depending on the population.

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The species most often confused with rugosus is its sister species, the Red Harvester Ant, Pogonomyrmex barbatus. The two overlap in range, look similar, and even hybridize in places. In his 1998 study on founding queens, Robert Johnson described them as ecologically equivalent sister species, with rugosus being the larger of the two. Typically, rugosus is darker and barbatus is solid orange. However, there is much research to be done in differentiating them.

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Where is Pogonomyrmex rugosus found?

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This species lives in desert grassland and desert scrub across the Southwest. We can ship them to Arizona, California, Colorado, Kansas, Nevada, New Mexico, Oklahoma, Texas, and Utah.

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Where rugosus and barbatus live near each other, they tend to split up the landscape. A 1976 study by Whitford, Johnson, and Ramirez in New Mexico found the two species avoid competing mostly through habitat selection, living in different parts of the same area. Johnson later showed (2000) that this split tracks soil texture and body size: the larger rugosus does better in some soils, and the smaller barbatus in others.

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Is Pogonomyrmex rugosus good for beginners?

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Yes, certainly a good beginner species, especially if you're able to provide heat. They're hardy and eager to grow. They're basically a seeds+heat=lots of workers formula. If you can't heat them, skip this species or find a heat cable or heat mat (both are fairly inexpensive). Avoid overcomplicating their setup, especially for a young colony. Keep it simple for the early stages. 

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When does Pogonomyrmex rugosus fly?

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In the desert Southwest, rugosus mating flights follow the summer monsoon rains (Johnson 1992). After a good soaking rain in May-August, winged queens and males leave the nest, mate, and the queens land and dig in.

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Typically they'll fly later on in the day, late afternoon or sunset.

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Founding and the queen

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Rugosus queens found their colonies fully claustrally (Johnson 2002). That means the queen seals herself in and raises her first workers using only the fat and muscle stored in her body. She doesn't need to leave to forage.

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What this means for you:

• No need to feed her. If you'd like, seeds can be provided, but this is optional. If the queen is struggling after weeks, then some seeds to keep her healthy may be a good idea.

• Open the tube as little as possible.

• Keep her warm and dark. Heat speeds up her brood, and darkness keeps her calm. If she is kept too cold, she won't grow. A simple heat cable at the very front of the tube might not be enough, this species tends to prefer heat closer and more intense. Just don't cook her, and don't eliminate the gradient completely. 

• Single-queen per colony. Queens will fight upon workers if they're kept together.

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Water matters more than you'd think

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This is where the research gets useful for keepers. In a 1998 study, Robert Johnson raised founding rugosus and barbatus queens at four different soil moisture levels in two different soil types, then tracked how they did.

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Water turned out to be the most important factor. As soil moisture went from low to moderate, almost everything got better: more queens survived, queens kept more of their body weight, more of them produced workers, and they raised more workers and brood. Past a moderate level, the benefits leveled off.

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Rugosus did handle dry conditions better than barbatus. In the driest treatment, more rugosus nests still had live workers. That's a nice safety margin, but it isn't a reason to let the tube dry out.

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For your setup, that means:

• Always make sure there is moisture in the test tube setup or nest.

• Aim for moderate moisture, not soaking. These aren't like moisture-loving ants of the southeast, far from it. They just need to have livable moisture levels in much of the nest. 

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Growth rate and colony size

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Once rugosus has workers and steady heat, they grow fast. With frequent protein feedings and consistently high temperatures, colonies can easily reach over 500 workers in their first year, probably much more if someone was doing superfeeding with them. Bigger colonies tend to slow down a bit, often due to less food or heat but they stay busy.

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The start can feel slow, though, and that's normal. Johnson (1998) found that barbatus has a higher metabolic rate and produces its first workers sooner than the larger rugosus. If you've kept barbatus before, expect rugosus to take a little longer to get going. This could be something to do with temperature, so we're hoping to do more testing with this species soon!

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Temperature and humidity

These are true desert ants, and they love heat.

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• Target temperature: 90°F for much of the nest, with a small section that is cooler.

• Give them a gradient. Heat one section of the nest and let them choose. Watch where they put their brood, and you'll learn what they want. Typically, if there's moisture there, they'll nest in the area with high heat.

• In a test tube, heat only the front (the end with the queen) or middle, never the water reservoir. A heated reservoir causes condensation and can flood the tube.

• Cooler temperatures slow everything down: less brood, less food taken, less eggs being laid. 

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Humidity: keep much of the nesting area humid, with some dry areas for storing seeds within the setup.

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Keep a backup test tube with water connected to the nest or outworld so they always have a drink. It's just a good idea to have that in place. Better to find the colony relocating into the water test tube as your warning sign than to find them dying and dehydrated.

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Do Pogonomyrmex rugosus need hibernation?

No, they don't. If you can help it, keep them warm year-round and they will continue growth. If you wish to diapause them, simply cool them down to 45-50ish for a few weeks and make sure they still have seeds and moisture in the nest. 

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Whatever you do, never let them get near freezing, and keep seeds available in the colony.

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Choosing a nest

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Grout or Ultracal (a hard plaster) nests, with a large area that has high humidity, but also sections that can be dry.

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A good rule: move them into a nest once they'll fill about half to two-thirds of it. Too much space too early can stress a small colony, unless they're using part of the nest for seed storage. Don't overcomplicate their setup, especially when the colony is young.

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On the sting: rugosus can sting, and it hurts. Use a barrier (like fluon or a talc mix) on the outworld walls, keep a lid on, and handle the setup with care. 

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Feeding Pogonomyrmex rugosus

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Seeds come first. Ensure there is a constant pile of seeds in the nest, and growing, meaning you're adding fresh seeds often no matter what. The workers will collect them, store them in chambers, and dump the husks and waste in a trash pile. Dandelion, Kentucky Bluegrass, Sand Lovegrass, Nyjer, all good seeds to give this species.

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Protein makes them grow faster. If this is what you want, offer protein regularly:

• Mealworm chunks

• Crickets

• Fruit flies

• Roaches

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Match the amount of protein to the size of the larvae pile. More larvae means more protein.

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I don't typically give this species liquid sugars, since it tends to cause a mess and they get their carbohydrate needs from seeds.

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Remove leftover protein within 16-24 hours to prevent mold. Seeds can stay in the setup, but husks should be removed frequently too.

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When are they most active?

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In the wild, rugosus activity changes with the season. Whitford and colleagues (1976) found rugosus was most active in mid-summer, and in July they foraged mostly at night to avoid the hottest part of the day.

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If your colony goes quiet for a while, it isn't necessarily problematic. Check temperature, especially. The most common reason for a Pogonomyrmex rugosus colony to not be growing is that they're too cold, even if you have heat somewhere in the setup.

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Common questions

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Do Pogonomyrmex rugosus need heat? Yes. They're desert ants, and heat drives everything: brood growth, feeding, and activity. At room temperature they grow very slowly. 90 degrees or warmer for the heated areas.

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Do Pogonomyrmex rugosus sting? Yes, and it's painful. Use a barrier and a lid, and handle the setup with care. In most cases, antkeepers don't need to handle the ants directly at all. Keepers with giant colonies can avoid being stung ever.

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How fast do Pogonomyrmex rugosus grow? With steady heat and regular protein, colonies can easily top 500 workers in the first year. Their first workers tend to come a bit slower than barbatus, but that's negligible.

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What's the difference between Pogonomyrmex rugosus and Pogonomyrmex barbatus? They're close sister species. Rugosus is larger and handles drought a little better. Barbatus has a higher metabolic rate and produces its first workers sooner (Johnson 1998). In the wild, they tend to live in different habitats and soils (Whitford et al. 1976; Johnson 2000). See our Pogonomyrmex barbatus care sheet for more.

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Do founding rugosus queens need water? Yes. Johnson (1998) found that soil moisture was the biggest factor in founding success, with survival and worker production improving from low to moderate moisture. Keep them in a test tube setup, which should provide the ideal moisture for just about any ant.

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What do Pogonomyrmex rugosus eat? Seeds, plus protein such as mealworm chunks, crickets, fruit flies, and roaches. No liquid sugars necessary.

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Do Pogonomyrmex rugosus need to hibernate? No, but they can do a low-level hibernation (diapause) at cold but not freezing temperatures if the keeper desires. Otherwise, they'll grow year round.

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Have questions or want to share your colony? Join the Stateside Ants community on Discord!

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Ready to start your own? Get your Black Harvester Ant colony here.

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Related care sheets: Pogonomyrmex barbatus · Pogonomyrmex occidentalis · All care sheets

References

Johnson, R.A. (1992). Soil texture as an influence on the distribution of the desert seed-harvester ants Pogonomyrmex rugosus and Messor pergandei. Oecologia 89: 118-124.

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Johnson, R.A. (1998). Foundress survival and brood production in the desert seed-harvester ants Pogonomyrmex rugosus and P. barbatus (Hymenoptera, Formicidae). Insectes Sociaux 45: 255-266.

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Johnson, R.A. (2000). Habitat segregation based on soil texture and body size in the seed-harvester ants Pogonomyrmex rugosus and P. barbatus. Ecological Entomology 25: 403-412.

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Johnson, R.A. (2002). Semi-claustral colony founding in the seed-harvester ant Pogonomyrmex californicus: a comparative analysis of colony founding strategies. Oecologia 132: 60-67.

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Whitford, W.G., Johnson, P., and Ramirez, J. (1976). Comparative ecology of the harvester ants Pogonomyrmex barbatus (F. Smith) and Pogonomyrmex rugosus (Emery). Insectes Sociaux 23: 117-132.

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