Pikes/Pines | Myrmecochory — Ants will plant your Capitol Hill garden for you (but only if you let them)

When I’m on my hands and knees in my garden, I almost always find something interesting. A solitary bee nest, evidence of a towhee scratching for grubs in the leaf litter, a slug trail wending through my seedlings. Recently I was weeding a corner of the house to make room for some native stonecrop I just planted and noticed something peculiar. A native plant, Western Starflower (Lysimachia latifolia), was growing alongside the stonecrop. A bonus, but also a bit of a mystery. The only other starflowers in my yard are at least a hundred yards away and, so far as I know, none are growing anywhere nearby, wild or otherwise. How did they spread to this random corner of my house?

As it turns out, a hint was right next to where I was sitting, in the form of another plant—Pacific Bleeding-Heart (Dicentra formosa). They are well known for a mutualistic relationship that helps them spread their seeds far and wide. I already knew that the bleeding-heart all over the yard didn’t appear by magic; ants were spreading their seeds in a behavior that is so well known that it even has a name: myrmecochory.

Ants are well-known ecosystem engineers, managing other insects for food, harvesting and spreading fungi, even altering soil chemistry. Many of us can attest to their impacts within our interior ecosystems. Despite their diminutive size, ants can be mighty bothersome when they show up in unwanted places. I don’t welcome ants into my home and try hard not to encourage them by leaving sweet things to lure them in, but I am happy to coexist with them outside my home where various species, introduced and native, help spread native plants in my garden. Myrmecochory, the act of ants acting as plant seed dispersers, is a well-known behavior, and according to the Xerces Society, over 11,000 plant species worldwide rely on this type of mutualism.

A classic example of myrmecochory, and where I first heard of the phenomenon, involves the Pacific Bleeding-Heart. Later this year, after the lovely little hearts have been pollinated and swell with seed, they grow a little something extra attached to each seed—a little reward for local ants, called an elaiosome. This oily treat is an ant magnet and it gets dragged back to the colony where the fat is eaten off, leaving a seed that is either carried away or left within the colony in a midden. Either way, these seeds travel and typically are deposited in a nice, well-aerated mulch rich with beneficial microorganisms, ready for germination. There’s a nice patch of Pacific Bleeding-Heart in Interlaken Park, no doubt spread by attention from ants.

Plants harnessing outside forces for seed dispersal isn’t nothing new or unique—it’s kinda the status quo. We know that plants use wind, such as maples or dandelions—called anemochory. And animals other than ants are excellent forms of conveyance (zoochory)—think of the little purple poos you see from birds during blackberry season or the sticky burs from Catchweed Bedstraw that hitch rides on our socks. So I don’t know why I was so astounded or surprised when I realized ants were carrying seeds around the yard, but maybe it’s because it just feels so intentional and more nuanced than just riding the wind (no shade on maple samaras).

Many well-known and loved native plants rely on myrmecochory. Wild Ginger (Asarum caudatum) and Western Trillium (Trillium ovatum) both use ants for seed dispersal. And when you visit a healthy forest ecosystem west of the Cascades, you’ll notice that where there are flowers in abundance there are often healthy Western Thatch Ant (Formica obscuripes) colonies, the most abundant and visibly active native ants in our region. (Sadly I don’t think thatch ants exist on the Hill anymore—but hey, I’d love for someone to prove me wrong.)

Despite all this, I haven’t been able to find anything but passing mention of Western Starflowers being myrmecochorous. However, even casual mention seems to confirm what feels most likely—the ants took seeds from the starflowers I planted elsewhere and brought them to where I discovered them this spring. Many plants can spread both through sexual reproduction (by producing seeds that ripen after pollination) and vegetatively, spreading via rhizomes or even just rerooting when a stem makes sufficient ground contact. Western Starflowers are no exception and have happily spread by underground tubers and by seed throughout the areas I’ve intentionally planted them. There’s a chance I somehow spread them by inadvertently digging up a tuber, but that feels even more far-fetched than ants moving their seeds around the yard.

Things like myrmecochory remind me that the world is endlessly interesting. Even in my garden, which is often the main place I interact with nature on a regular basis (which is why it comes up on Pikes/Pines so frequently), I can feel intense wonder. (Even when I delve into the complexities and learn that myrmecochory may also aid in the spread of invasive plants like thistle.) Next time you find a plant out of place in whatever spaces you tend, be curious; maybe it’s more complex than you expected—indeed, most things are.

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