Prior to my recent Costa Rican trip, I would not have expected that ants can be so fascinating! Specifically, Leafcutter Ants. These ants are commonplace throughout central and south America, and in some parts of southern U.S. from what I’ve read. They are also agricultural pests that can decimate crops. I have a few photos to share and have given myself an assignment to capture a better photographic story of their life and behavior on my next trip to Costa Rica.
As seen in this first photo, Leafcutter Ants carve pieces from fresh, green leaves and carry them back to their nest. Regretfully, I don’t have a photo of the long line of ants carrying their leaf fragments to a very large nest that may be 100 yards or more from the harvesting site. But, what do they DO with these leaf bits?
The ant shown here is about a quarter or three-eighths inch in length. The difficulty of capturing this photo is another story. Briefly, I used a Nikon 105mm macro lens and an off-camera flash held in my hand, while the camera was mounted on a tripod. Exposure was 1/60th sec at f32. This particular parade of ants was marching down a tree trunk and my camera was on its side about 4 feet from the ground. I rotated the photo 90 degrees for easier viewing. Most leafcutter ants were seen following their well-established and cleared paths on the ground, where they are much more difficult to photograph!
I learned much more about these ants after returning home and discovering a book titled (what else?), “The Leafcutter Ants: Civilization by Instinct,” by Bert Hölldobler and Edward O. Wilson. I found this book while reading Philip Davison’s excellent blog; Philip is a biologist who has lived on the Osa Peninsula for 20 years and leads educational tours at Bosque del Cabo lodge.
So, what do these gals (yes, they are ALL female) do with the leaves? They don’t eat them, they use leaf bits to grow a fluffy gray fungus, which they then consume. Within the nest, this fungus grows on walls built from a papier-mâché paste that is manufactured from the fragments of vegetation brought in by the foraging workers.
A mature Leaftcutter Ant colony has several million members and is organized by a strict caste system, with substantial differences in size among subclasses of its all-female family. All daughters in a nest are offspring of a single queen who may produce 150 to 200 million daughters during her 10 year lifetime. The story of harvesting and caste delegation is explained very well in the cited book:
After the returning foragers drop the pieces of vegetation onto the floor of the nest chamber, the pieces are picked up by workers of slightly smaller size, who clip them into fragments about 1 to 2 millimeters across. Within minutes, still smaller ants take over, crush and mold the fragments into moist pellets, add fecal droplets, and carefully insert them into a mass of similar material. Next, workers even smaller than those just described pluck loose strands of fungus from places of dense growth and plant them on the newly constructed surfaces. Finally, the very smallest and most abundant workers patrol the beds of fungal strands, delicately probing them with their antennae, licking their surfaces, and plucking out spores and hyphae of alien species of mold.
Wow! The harvesting workers that I photographed are only the tip of this organizational iceberg. Another caste role that I read about, but didn’t see in the field, are very small sisters that look like pygmy replicas of the foraging workers and often ride as “hitchhikers”on the leaves carried by their larger nestmates. No, they are not lazy, but serve an important function of protecting their sisters from parasitic flies that attempt to lay eggs upon the necks of the larger ants. The hitchhikers serve as living flywhisks! On my next trip to Costa Rica, I hope to see and photograph these helpful little sisters.
A mature leafcutter ant nest will produce only a few male ants per year, whose only goal is to leave the nest and mate with other virgin queens. Then they die. The new queen left her original nest holding a small cache of fungus that she will now use while attempting to dig and start a new colony. From her single mating with a male, she stores more than 200 million sperm cells that will allow her to fertilize eggs for the remainder of her lifetime. For ladies reading this story, don’t get any ideas about world domination!