Our native trilliums (Trillium ovatum) are starting to bloom in the wooded areas. When I first moved to the Pacific Northwest, it was nice to see trilliums again: the sessile-flowered trillium (Trillium sessile) grew in abundance in the woods behind the house I had lived in in Illinois, and I had missed these flowers since moving to the Rockies.

Trilliums bloom in abundance in many wooded areas on the island, too. They are not nearly so abundant in the remaining wooded areas across the Salish Sea in Seattle. My guess is that this discrepancy has to do with ants.

The native western thatching ant (Formica obscuripes) is still commonly found on the island. Those are the ants that build large nests of conifer needles, small twigs, and other forest-floor debris. The nests are normally about 1 foot high and two or three feet wide, but in exceptional cases I’ve seen ones five feet high and a dozen or more feet wide(!).

They have something of a reputation for being aggressive, but I have personally found this to be undeserved: many a time I have stood at the edge of a large anthill, and been undisturbed by the many hundreds of ants entering and exiting at any given time. If you bend down and listen closely on a warm day when the ants are particularly active, you can hear a slight rustling sound from the collective activity of those hundreds.

What do ants have to do with trilliums? Trillium seeds have an oily appendage that ants are particularly fond of, so ants tend to harvest trillium seeds, often carrying them some distance before they separate the appendage from the rest of the seed.

Our native thatching ants are significantly larger than most of the (generally introduced) ants one see in cities. Being larger, they can more easily carry and disperse trillium seeds. If the smaller ants eat trillium fruits, they would probably tend to eat them off the seeds where the seeds fell, instead of first carrying the seeds some distance.

It can be bad for a baby plant to grow too close to its parent. Suppose the parent needs some nutrient which is in short supply in the soil to start with; that would make the soil in the vicinity of it, deprived in that nutrient because the parent has taken much of it, a poor place for its children to try and get a start. Plants have evolved seed dispersal strategies for a reason.

If my theory is correct, the lack of effective seed dispersal due to the missing ants has proved harmful to Seattle’s trilliums; not enough children have survived in order to replace their parents, and over time populations have dwindled there.

“When we try to pick out anything by itself, we find it hitched to everything else in the Universe.”—John Muir.