Feeling Antsy

Ants are everywhere, but only occasionally noticed. They run much of the terrestrial world as the premier soil turners, channelers of energy, dominatrices of the insect fauna…

~Bert Holldobler

The more I learn about them, the more I appreciate plants. Working at the NC Botanical Garden allows me to see the passage of time through the eyes of a variety of native plant species. I have witnessed slow, long-term seasonal changes, as well as brief glimpses of wonder. And so it was that last Friday when a coworker came in right before closing and showed me her phone video of ants dispersing the seeds of a trillium in the Herb Garden. It was amazing to see them carrying such a huge load across the rocks. I grabbed my camera and headed over, hoping I wasn’t too late.

side view of ant carry trillium seed

An ant carrying a Trillium seed back to its nest (click photos to enlarge)

I have seen this phenomenon, called myrmecochory (seed dispersal by ants), a few times before and reported on it in an earlier post. Estimates are that 30%-40% of our spring-blooming woodland flowers rely on ants for seed dispersal. Another source stated that elaiosomes occur in over 11,000 plant species! There are various theories as to why ants do this and how it benefits the seeds:

  • the lipid-rich appendage is a food reward that is fed to the ant larvae when it is taken back to the nest
  • the seed is dispersed away from the parent plant, which may provide a better growth environment by reducing parent-offspring or sibling competition
  • by quickly transporting the seed to its nest, the ants’ behavior reduces the time the seed may be exposed to various seed predators (the seed might get eaten by a bird or mouse, for example)
  • when the seed is discarded into the ant “trash pile”, it is in a nutrient-rich environment ideal for germination

In addition, one author speculates there may be some benefit from the anti-microbial properties within ant nests that will reduce the susceptibility of the seed to various pathogens.

Studies where a researcher has removed some of the elaiosomes and compared removal rates have shown that ants remove seeds with elaiosomes more quickly, often using the appendage as a handle.

But the most intriguing research I have seen focuses on the reason the ants pick up the seed in the first place. It seems that elaiosomes rich in oleic acid trigger a stereotyped carrying  behavior in a variety of ants. E.O. Wilson, the dean of ant researchers, showed that a dead ant starts emitting oleic acid about 48 hours after its death. This is a signal to other ants to pick it up and carry it back to the nest and discard it. He even added a drop of the “dead ant” acid to a live ant, which was quickly picked up and carried to the trash pile, in spite of its thrashing and obviously living qualities. To quote an NPR story on this experiment, Dead is what you smell — not what you see — if you are an ant. So, do plants mimic an insect chemical in order to get ants to carry out their seed dispersal tasks? It appears there may also be some benefit to the ants in this relationship, but the origins of this behavior are fascinating to ponder.

Below is a series of images depicting about 45 minutes in the long life story of one wildflower – a plant that may take 2 years for its seed to germinate, and then another 5 or 6 years to flower and produce its first seed. And, it seems to have figured out a way to con a bunch of insects (yellow jackets are also known to disperse seed with elaiosomes) to carry its seeds back to their trash pile. There appears to be a lot going on out there in the woods that we are just beginning to understand. All the more reason to plant some native plants and get outside and observe your wild neighbors.

Trillium cuneatum

The source of the seeds – Little Sweet Betsy, Trillium cuneatum (this photo was taken in another location in the garden back on March)


This is how the Trillium that provided the seeds looks now (this photo was taken a couple of days after the ant dispersal images and the seed pod has now disappeared)

trillium seed pod

The seed pod was lying on a leaf and was laden with ants

Trillium seed pod with ants inside

A peek inside at the seeds with elaiosomes and ants

ant carrying seed out of seed pod

An ant lugs a seed up and out of the pod

ant carrying seed down the plant

Then it is easy-going downhill on a leaf

ant carrying trilliun seed by the elaiosome

Then on to a lichen- and moss-covered rock

ant about to drop off steep edge of rock with seed

The first hazard on the journey – the steep drop-off of the front edge of the rock (as I watched, a fewants fell off this ledge with their heavy loads)

Ants on trillium seeds in Herb Garden

A feast when a few seeds fell out onto the rock

ant carrying trilliun seed by the elaiosome 1

The elaiosome provides a good grip for an ant’s jaws


The path taken by the ants – about 6 feet across an open walkway to the rock in the background

ant nearing nest entrance under leaves

An ant with its prize just before disappearing into the nest beneath the leaf litter

Ants In My Plants

It’s not enough to be busy, so are the ants. The question is, what are we busy about?

~Henry David Thoreau

I think we all fall into that trap sometimes, perhaps too often – just being busy for the sake of being busy. It was probably more true for me when given some seemingly meaningless paperwork task during my work years rather than now in my retirement (and, thankfully, that did not happen all that often in my career). And it is true that ants are busy creatures, all too busy for us if they manage to find ways into our houses. I do know one thing that ants are very busy about this time of year – and that is plants. Certain species of tropical leaf cutter ants are well known for their leaf collecting and fungus farming. It turns out our local ants do a lot of interesting things as well. They can serve as pollinators for some species of plants and nectar thieves for others. In fact, many plants have evolved clever ways to hinder access to their flowers by ground-dwelling insects like ants, presumably because these crawlers often raid the nectar without performing the efficient pollination of aerial insects. Hairy stems and sticky solutions from glands are but two of the mechanisms used to deter these raiders. But, in our spring woodlands, ants play another, often overlooked function. But you have to look closely to learn more…

Bloodroot seed pod backlit

Bloodroot seed pod as it starts to form (click photos to enlarge)

Yesterday, I shared some images of the Bloodroot flowers blooming in the yard. The petals on many of the plants are now gone, barely visible in the leaf litter. The stalk that once held the brilliant white flower is now topped with a slender green capsule.

Bloodroot seed pod mature

Mature Bloodroot seed pod showing how it splits to release seeds

To tell the rest of the Bloodroot story, I’ll need to borrow some images from the archives. These Boodroot seed photos were taken on a trip to the Smokies a couple of years ago in early May, a time equivalent to perhaps mid-April in these parts. I stopped to photograph some wildflowers and noticed the distinctive leaves and seed pods of a clump of Bloodroot. I could see one of the pods had split open and there were only a couple of seeds visible inside the pod, so I looked on the ground below.

Bloodroot seed on ground

Bloodroot seed on the ground beneath an open pod

Bloodroot seeds fall to the ground beneath the parent plant, a situation that is usually not ideal for a plant, due to potential limits of space, sunlight, nutrients, etc. This is why plants have evolved so many interesting means of seed dispersal using wind, water, and animals to help move their seeds to more favorable areas for successful germination. In the case of Bloodroot, and many of our other spring woodland flowers, that seed dispersal mechanism is directly related to ants. And the ants are not doing it out of the goodness of their tiny hearts, but rather for a self-serving reason related to that great motivator, food. You may notice the Bloodroot seed looks a bit odd, not much like the seeds you buy to plant in your yard. This seed looks like it has a polka-dot slug riding on it, or perhaps it has a plant version of a punk hairdo. What it really has is a lipid-rich appendage called an elaiosome (Greek élaion “oil” and sóma “body”).

Ant carrying Bloodroot seed

Ant picking up a Bloodroot seed

These lipid and protein-rich bodies are very attractive to ants and a variety of species of ants somehow manage to find these seeds soon after they fall to the ground. After reading about this phenomenon, I had tried to photograph it in my yard in Raleigh, where I had Trout Lilies planted in a natural area. I collected some seeds and laid them out on a piece of paper, hoping to see some ants come and collect them. I went inside to get my camera, and stayed in for a little too long it seems, because when I returned a short while later, all the seeds were gone. On this day in the mountains, I started looking around the plants and found several ants crawling about. I waited only a few minutes before an ant found one of the seeds ( I had brushed aside some leaf litter to make it easier to photograph the scene).

Ant carrying Bloodroot seed 1

Ant carrying Bloodroot seed

The ant quickly picked up the seed and struggled to carry it off, presumably to its nest. Ants eat the elaiosome (some say they also feed it to their larvae), and discard the seed. The seed has thus been transported away from the parent plant at least some distance, and often deposited underground in an ant nest trash pile, usually a great spot for germination and protection from potential seed predators like Deer Mice. One research paper I saw stated that the elaiosome itself may also provide some chemical deterrent to certain mammalian seed predators. This fascinating process of seed dispersal by ants has an equally fascinating name – myrmecochory. Some researchers say as many as 40% of the herbaceous species in some temperate woodlands like we have here in North Carolina rely on ants for their seed dispersal.

Bloodroot seed pod in early stage of development

Bloodroot seed pod in early stage of development

So, when you are in the woods these next few weeks, take a moment to ponder the miracles happening beneath your feet, and take a closer look to see if you, too, have ants in your plants. I know I’ll be looking, camera in hand.