Colonies of Atta dig out large open chambers in the soil and start their fungus gardens on rocks and the roots of plants. Rarely do you find their gardens touching the soil directly because there is the risk of contamination by foreign pathogens and unwanted fungi. Leaves are chewed into smaller pieces and the fungus gardens themselves become the nest structure. Brood is put directly in contact with the fungus and allowed to feed.
Trachymyrmex is a more common genus throughout the US. Unlike Atta and Acromyrmex, they're not restricted to the Mexico boarder and parts of California. Their colonies are much smaller though and they their caste system is nothing compared to the diversity in Atta. Queens of Trachymyrmex are barely larger than the workers.
Colonies are much smaller too, possessing only 1 to 4 fungus gardens, typically. There's also a higher focus on collecting fresh plant debris that's already fallen from the plant. They're also far more willing to use caterpillar and grasshopper frass. In Doug Tallamy's "Bringing Nature Home" he lists 535 species of Lepidoptera (moths and butterflies) use Oak trees as host plants alone. That's a lot of crap raining down to the forest floor every day.
Here a Trachymyrmex septentrionalis worker is carrying a piece of caterpillar frass back to the nest.
The two main strategies of surviving the arid parts of the US were to focus either on seeds or nectar storage. Harvester ants, as their name suggests, focused on seeds.
For the most part, adult ants can not consume solid food. But new research has found that some species and or whole subfamilies of ant genera have adult members that can consume solid food.
Ant Seed Dispersal (Myrmecochory)
Yellow Trout Lily
White Trout Lily
Trout Lilies don't always flower. Often they favor division to form a vast colony of spotted leaves along the forest floor. When they do flower it's often because they're growing in rocky soil or because their roots can't expand easily outward in any particular direction, thus energy is put towards flowering. A gardening trick is to either treat this as a potted plant or to mix in a few rocks into the soil beneath the plant roots to help encourage this. The resulting seed pod is later laid on the ground for ants to come and find the seeds which have packets of elaiosome on them.
Bloodroot, Sanguinaria canadensis, emerges early in the spring with its leaf clutching its flower stem to help protect it against harsh winds.This species is in the poppy family, thus the flower doesn't produce any nectar, just pollen. After pollination occurs, the flower develops into a seed pod and is laid directly down on the forest floor where it eventually opens for ants to partake of. Bloodroot gets its name from the red sap excreted by the root of the plant.
Stylophorum diphyllum, is probably the easiest ephemeral to grow in North America. Plants produce multiple flowers for a long period of time in the spring, and seed pods are produce well into June and July.
Ants are not required for this plant to spread but seeds are still coated with elaiosome all the same. Unlike other ephemerals this species spreads quick for a woodland plant, with seeds germinating only after one year of dormancy. Plants usually flower from their third year on.
Trillium erectum, Red Trillium, is a beautiful plant with a bright red flower. Plants are monofloral producing just one bloom if any for the whole year. They're pollinated by carrion flies and beetles, thus the flower smells of rotting fish, thankfully one has to put their nose up to the flower to observe this fact. The seed pod develops at the end of the stem where the flower used to be, often hanging down below the leaves at this time where it eventually opens or falls to the ground for ants to partake of.
Turkey Corn, Dicentra exima, and Dutchmen's Britches, Dicentra cucullaria are native versions of a plant called Bleeding Hearts. I favor Turkey Corn because it blooms off and on all year long and almost always had a seed pod ready to pick and disperse to the ants.
Hepatica, a.k.a. Liver Leaf but I've never heard anyone refer to it as that. The name hark-ins back to a time when herbalists believed plants shaped like human organs possessed medicine to treat ailments relating to that organ. In other words quackery. Hepatica is a semi-evergreen with a charming rosette of leaves around it all year long. Mid winter though the leaves die off and fade away, making room for droves of flowers to spring up in late winter, early spring. New leaves are later formed that last the whole year. Flowers are most often white but shades of blue, pink, and lavender are not uncommon. Seeds form at the ends of the flower heads as a pointed star-like mace but eventually break apart into individual seeds tipped with elaiosome on each one. I've never witnessed ants taking any interest in these though.
A damaged Trillium seedpod is an open buffet. The majority of ant species that find the seeds would rather feed on the eliasome in place than bother carrying the seeds back home with them. Here Camponotus subbarbatus workers collect the nutrients from the elaiosome until they're completely dry, but not one of them bothered to move the seeds anywhere. Crematogaster and Nylanderia both do the same thing.
The issue seems to be a matter of size. The most ideal ant genus I've found up for the job in the US anything in the genus Aphaenogaster. It's very likely the similar Myrmica species also do a good job but I haven't had a chance to test that. I've also seen Formica and some members of the Camponotus genus also work but many of these don't nest in ideal locations. That's not necessarily a bad thing though. Seeds are often discarded out of the nest. But if they're abandoned inside a dead log, the seed doesn't have much chance to grow as early as it would like to.
Turkey Corn, Dicentra exima, is another plant I've had success with getting Apheanogaster to take an interest in. Thus far though I have not seen any new plants sprouting out of the ground.
Ant Pollination is a tricky topic because it implies the plant evolved to be pollinated specifically by ants instead of the more efficient bees, beetles, flies, birds and bats. There are three plant species native to the U.S. known to be pollinated by ants and are listed as follows: Paronychia pulvinata, Diamorpha smallii, and Polygonum cascadense. In all three cases the pollinator was a member of the genus Formica. In all three cases, plants were species that grew very low to the ground so the ants could easily move from one plant to the other. Often the plants were of a creeping habit, and possessed an abundance of flowers that all had a simple in structure to them.
Ants are believed to be terrible pollinators because they're coated in a type of antibiotic that destroys pollen on contact. I contest though a single ant can only be coated in so much of this chemical before the pollen it is rendered useless, and that pollen to some plants can surely attach itself to the ant's hairs or otherwise cake onto the ant's body.
Asclepias purpurascens, an uncommon and often hard to grow perennial. Unlike most other Milkweed species, Purple Milkweed requires cross pollination with a different plant in order to produce viable seed. Unfortunately it's things as simple as this that discourage pollinators from even visiting the flowers.
Extrafloral Nectar and Nectar Scraping
Many plants are coated in a thin layer of nectar which the ants collect by "nectar scraping." This most often occurs on the leaves and new growth, but some plants have evolved to help protect their flower buds by coating them in a thin layer of sweet plant sap. This is the help defend against certain types of moths that lay their eggs directly in the unopened flower buds of certain plants. Without the ants protecting the flower bud, the resulting caterpillar is free to burrow into a flower bud and consume the reproductive parts before the bud has a chance to open.
Hemipterans (Aphids, Scales and Mealy Bugs)
In the absence of rich flower nectar or pores specifically designed to feed ants, aphids and other types of dew producing insects may provide the "service" to the plant. I say "service" because the host plant in question doesn't have any real way of regulating how many aphids, scales, or mealy bugs infest the plant.
Zizia aurea. Oddly enough this species seems to vanish or more onto a different host plant after flowering has finished. A different species then occurs on the plant around the seed pods.
Plant Defenses Against Ants
Rhododendron calendulaceum, has the stems leading up to its flowers covered in special hairs that produce a sticky sap, stopping the ants in their tracks. Coating the back of the flower also offers a tasty treat to any hummingbirds that may show up to the flowers looking for a meal.
Caterpillars Ant Interactions
There are actually species of caterpillars that catapult their frass away from them specifically to lore ants in that direction.
Some species of Butterfly in this subfamily later switch from feeding on the plant matter to feeding on the ant brood and are escorted into the nest where they go on to mimic the brood they feed on as well as sounds a queen ant would make when demanding food. Not all species have to over winter within an ant nest, but those that do are often threatened or endangered. Not only do they require the right host plant(s) but also the right host ants. So you can have a pristine meadow of host plants but if the wrong species of ant is present this might break the chain.
I don't know of any particular examples of ants not working out as hosts, but many species find butterfly eggs to be a food source, so if something invasive moves in, such as the Red Imported Fire Ant, Solenopsis invicta, they may be more preference at removing the eggs right off the host plant. I'm sure native ant species do this as well, but it's unlikely to be done on such a scale to eradicate the population.
Limenitis arthemis, Red Spotted Purples, construct a stick out of silk and their own frass at the tips of the leaves they consume. Ants do not walk over this structure, and caterpillars will flee back to it once they sense the ants coming. However, this doesn't work all the time. I suspect some species of ants are able to reach them better than others. I say this because of the video below and my own experience.
Doug Tallamy's Black Cherry Trees are completely defoliated thanks to Red Spotted Purple and a few other species. I have a Black Cherry of similar height in my yard but it's never been defoliated. All of the leaves do have some amount of caterpillar damage (a distinctive chewing line cut out through the leaf) but I never see any Red Spotted Purples making it past the first instar. I believe this is thanks to two species of Camponotus and a Formica that forage on the plant all day and night.