9 minute read
Ants! At the Disc Golf Course
By Zach Phillips, Ph.D., Terrestrial Invertebrate Conservation Ecologist
I do not play disc golf, but I rate the disc golf course at Elings Park very highly: five out of five Frisbees. My course rating system, which disc golfers might consider slightly unorthodox, is based entirely on ants. Are there interesting ants on the course? This is the only criterion. The course design could be perfect, the views spectacular, and the disc baskets (Figure 1) well maintained, but all this would be beside the point. Show me the ants.
The Elings Park Disc Golf Course is home to harvester ants (Pogonomyrmex spp.), an outstanding group of insects: five out of five abdomens. Harvester ants are key components of California’s ecosystems, particularly in deserts and other dry habitats. They construct deep underground nests and move large amounts of soil, dramatically altering the physical environment. To help carry fine particles of sand, each ant uses a “beard,” a set of long hairs on the underside of its head (note: pogonomyrmex means “bearded ant”) (Figure 2). Facial hair has never been so chic yet ecologically functional. The ants are also dominant granivores aka seed eaters (Figure 3 and 8) and influence plant and animal communities by transporting and consuming a wide variety of seed (Uhey et al., 2022).
Seed Foraging
Seeds are a major part of the harvester ant diet, and colony members perform seed-related tasks inside and outside of the nest. Foragers hunt down individual seeds, carry them back to the nest, and drop their quarry just inside the entrance. From there, a different set of workers transports and processes the seed within the nest’s underground chambers. Each seed is de-husked, broken down into a dish called “ant bread,” and stored in granaries or fed to maggot-like ant larvae. The seed chaffs, along with other colony waste, are dumped outside the nest in a refuse pile or “midden” (Figure 4). Harvester ant middens are largely made up of discarded plant material. They are pleasant, aromatic green-bin garbage dumps. With the right branding, you could sell them as ant-artisanal potpourri — “PogonAroma: One Ant’s Trash Is Another Man’s Treasure” (Figure 5).
On the disc golf course at Elings, middens encircle the nest mounds of California harvester ants (Pogonomyrmex californicus). In autumn 2024, the middens were dense with rust-red parts of California buckwheat (Eriogonum fasciculatum) (Figure 6), a feature that suggests the plant is a favored colony food source. However, a midden’s content does not necessarily mirror a colony’s diet, and plant matter can be deposited in refuse piles for multiple reasons. For example, the ants might be adding California buckwheat fragments to middens to help absorb moisture around nest mounds or to mark nest boundaries (Gordon, 1984). Regardless, the ants’ diet and waste should change with changing seed availability over the year. Colonies are not dependent on a single plant species, and their seed preferences are affected by factors such as seed size, shape, and seasonal abundance.
Seed Dispersal
Even though a colony functions like a well-oiled machine, individual ants operate like Larry, Curly, and Moe. They bump into things, get discombobulated, spin around, and get mad at each other. A clumsy ant can be a good thing for a seed. It’s not uncommon for a harvester ant forager to fumble and abandon a seed on its way back to the nest. When this happens, the ant has helped move the seed from one place to another, facilitating its dispersal and sparing it from an “ant bread” fate (Mull, 2003).
Seed successfully carried back to the colony can also be spared. Healthy seeds are sometimes discarded into middens, where they can germinate and be shielded from other seed and seedling eaters (e.g., ant-phobic birds and rodents). Also, when colonies die or abandon their nests, viable seeds that remain in granaries can germinate and grow. Consequently, patches of distinct plant communities often develop on and around harvester ant nest mounds (Rissing, 1986).
Some plants use “elaiosomes” to conquer the whims of foragers. Elaiosomes are seed appendages that attract ants to aid in their dispersal. They are edible, detachable rewards, and look like little seed hats. The bush poppy (Dendromecon rigida) is a local example of a native plant that has evolved elaiosomes, and they attract harvester ants to help disperse their seed (Carney et al., 2003). A bewitched ant can use the elaiosome as a handle to carry the seed, eventually removing and eating it while leaving the rest of the seed unharmed. Thus, in this mutualism both the ant and the plant benefit from the interaction — the ant gets a meal, and the plant gets dispersed.
Enemy Ants
Harvester ants have powerful stings. On Justin O. Schmidt’s Pain Scale for Stinging Insects, which runs from one (least painful) to four (most painful), Florida harvester ants (Pogonomyrmex badius) earn a three. His verbal description of the pain is vivid: “Bold and unrelenting. Somebody using a power drill to excavate your ingrown toenail.”
Unfortunately, not even a world-class sting like this can save harvester ants from invasive Argentine ants (Linepithema humile), one of most destructive animals in California (Figure 7). Argentine ants are relatively tiny and lack a sting, but harvester ants are no match for their aggression, numbers, and chemical arsenal. The loss of harvester ants to Argentine ants sends damaging ripples across ecosystems, partly because the latter cannot replace the former as a resource for certain animals and plants. For example, horned lizards (Phrynosoma spp.), which specialize in eating harvester ants, show an aversion to Argentine ants (Suarez et al., 2000). Similarly, the seed of bush poppies, which you’ll recall use harvester ants for dispersal, are not dispersed by Argentine ants. (Carney et al., 2003)
A Healthy Discourse
Argentine ants are common in Elings Park, just like they are in the rest of Santa Barbara. How long can the harvester ants on the disc golf course hold out? Who knows, but we’d like to keep an eye on the population. Ecology Intern Ryan Tang, working with me at Santa Barbara Botanic Garden, is mapping the locations of the harvester ant nests, which will help us monitor their decline or persistence.
While looking for nests at Elings, Ryan and I regularly encounter friendly disc golfers who show an interest in the ants that share their course. We don’t even have to pique their curiosity with ant factoids customized for a disc golfer audience, such as, “The sting hurts like a Frisbee slamming into your ingrown toenail.”
On our last visit, we chatted for a bit with a group of golfers about our survey. About 20 minutes later, they excitedly called us over to another spot in the dunes. They’d found a nest, and we marked it with a flag.
Acknowledgments: Thanks to journalist and birder Hugh Ranson for his photo and Elings Park natural history observations; Garden Ecology Intern Ryan Tang and Garden Invertebrate Technician José Flores for their photos and survey help; Garden Director of Conservation and Research Denise Knapp, Ph.D., for plant identifications; Elings Park Executive Director Dean Noble for permission to wander the course; and all the disc golfers for sharing the space and not being disc-gruntled when I call it a “Frisbee.”
CITATIONS
Carney, S. E., Byerley, M. B., & Holway, D. A. (2003). Invasive Argentine ants (Linepithema humile) do not replace native ants as seed dispersers of Dendromecon rigida (Papaveraceae) in California, USA. Oecologia, 135, 576–582. https://doi.org/10.1007/s00442-003-1200-0
Gordon, D. (2008). The harvester ant (Pogonomyrmex badius) midden: refuse or boundary?. Ecological Entomology, 9, 403–412. http://doi.org/10.1111/j.1365-2311.1984.tb00837.x Mull, J. (2003). Dispersal of sagebrush-steppe seeds by the western harvester ant (Pogonomyrmex occidentalis). Western North American Naturalist, 63, 358–362.
Rissing, S. W. (1986). Indirect effects of granivory by harvester ants: plant species composition and reproductive increase near ant nests. Oecologia, 68(2), 231–234. https://doi.org/10.1007/ BF00384792
Schmidt Sting Pain Index: https://www.sciencefriday.com/segments/from-nettles-to-volcano-apain-scale-for-insect-stings/.
Suarez, A. V., Richmond, J. Q., & Case, T. J. (2000). Prey selection in horned lizards following the invasion of Argentine ants in Southern California. Ecological Applications, 10, 711–725. https:// doi.org/10.1890/1051-0761(2000)010[0711:PSIHLF]2.0.CO;2
Uhey, D. & Hofstetter, R. (2021). From Pests to Keystone Species: Ecosystem Influences and Human Perceptions of Harvester Ants (Pogonomyrmex Veromessor, and Messor spp.). Annals of the Entomological Society of America, 115(2), 127–140. https://doi.org/10.1093/aesa/saab046
