Friday, December 15, 2017

Leaf-cutter ants do wonders for the forest


Hitching a ride: A leaf-cutter ant carries a leaf, while smaller ants called minums hitch a ride. These minums act as a defence to make sure parasitic wasps don’t lay eggs on the workers carrying the load, and they also drink the sap from the edges of the leaf. —Photos courtesy James Wallace

Mark Fraser

IT only takes a few steps inside the rainforest until you realise why so many consider it nature’s wonderland. In the space of a few minut­es, we went from navigating our way along the narrow Blanchisseuse oad, passing road works and clouds of dust along the way, to trekking through a forested area, our view of the skies obscured by the canopy of trees up ahead. Around us there are dozens, maybe even hundreds of plant and animal species.

First the humidity hits you and your clothes begin to cling to your body, sweat gathers at your brow and in your armpits. Then you become completely absorbed by the sights: a hummingbird drinking the nectar from a flower, an agouti darting off in fear of these strange two-legged creatures invading its habitat, and the sounds—a waterfall in the distance, a medley of bird songs as colourful and unique as the birds themselves. There is another persistent high-pitched sound that follows us everywhere we go, it almost sounds as if there were a live electrical wire hanging above our heads.

“Cicadas,” said our guide, Denise Etienne, as if she had been reading our thoughts.

These tiny winged insects spend their time in trees mostly hidden from view, looking for a mate. The males flex organs found in their abdomen to create their song and attract a mate, while the females respond by flicking their wings, Etienne explained. The cicadas rely on clicks to attract a mate, while other species resort to some pretty fascinating tactics.

We come across a lek of white-bearded manakins. These “leks” refer to a grouping of males that gather to put on displays to entice females and they are usually formed during breeding season.

To attract a female, the white-bearded manakin clears a patch of ground and makes leaps from sticks to the ground. His leaps are accompanied by wing snaps which make loud popping sounds.

We stop in our tracks to observe the males in action—tiny birds with chests the colour of snow, leaping from stick to ground. Their counterparts, the golden-headed manakin, do things a bit differently. Instead of leaping from stick to ground, the males slide down a branch; Etienne compares it to a “moon-walk”.

This routine would repeat itself over and over again until a curious female finally comes along to investigate. And then, as with the cicadas and everything else in the forest, the cycle of life would begin all over again.

The birds and their fascinating yet comical attempts to lure females wasn’t the real reason the Express met up with Etienne, who is the education officer at Asa Wright Nature Centre. We were on a search for the “workers” of the forests: leaf-cutter ants or bachacs, as they’re commonly known. Some consider the leaf-cutter ants to be nothing more than a pest which devours the leaves of plants. But they are important contributors to a healthy forest—not only are bachacs the pruners of the forests, they help fertilise or add nutrients to the soil.

Leaf-cutter ants are picky choosers. They will travel great distances just to get the right type of leaf, which they then tote back to the nest.

Etienne leads us to what looks like a huge pile of sand dumped by a bulldozer.

On closer inspection, we notice it’s actually a large ant nest with several holes which not only help aerate the soil, but also act as tunnels for the multitudes of ants heading in and out. Etienne suspects this particular nest may be about five to six years old, which is still fairly new, she says. There are other ant colonies on the grounds of the nature centre that are ten years and older.

There is a layer of tiny bits of dried leaves coating the ant nest. Etienne believes these are the leaves that were rejected and then deposited outside the colony. We get down on our hands and knees to observe a trail of ants coming with their latest supplies, some carry bits of fruit, flowers or leaves. Inside this nest lives the ant queen. She can live for up to 30 years. All the ants we see marching in and out are her daughters—in their world, it’s the females that do the laborious work. These tiny ants can carry over 50 times their body weight, said Etienne.

Back inside the ant nest, which can go as deep as ten to 30 feet, the ants chew the leaves but don’t digest them. Instead, they regurgitate them then put a layer of faecal matter over what they’ve expelled. This helps to create a fungus. As the ants repeat

the process the fungus grows and then produces nodules rich in protein—this becomes the food source for the leaf-cutter ants, says Etienne.

The fungus itself resembles a spongy coral, and there are several of them in different chambers of the ant nest.

As we observe the leaf-cutter ants toting their loads, we notice little ants hitching a ride on their backs. These are called minums, she said. Their purpose is to drink the sap from the edges of the leaves so that nothing goes to waste, and also to prevent parasitic wasps from laying eggs on the workers carrying the precious cargo.

The ants constantly groom the fungus and any unwanted part of the fungus is discarded as trash in what is known as the “midden pile”, which beetles and other insects feed on. In turn, the legless lizard or two-headed snake feeds on the beetles so the ant colony is like an ecosystem within an ecosystem, says Etienne.

“I like to say that an ant nest could be compared to a proper functioning government. Everyone works: some bring in food and others act as excavators while some defend the nest. In an ant colo­ny, everyone has a role to play—it’s not about one ant, it’s about the entire colony; that’s why they’re so efficient,”she says.

Etienne started working at Asa Wright in 1995. Of all the wildlife she’s encountered, the leaf-cutter ants are among her favourites. Humans can learn a lot from these tiny creatures which we often take for granted, said Etienne.

“I am just fascinated by the leaf-cutter ants because they are so complex, well-organised, plus they exhibit great team spirit or camaraderie! I enjoy looking at them, down to their tiniest details, they are very strategic,” she said.

For Etienne, the rainforest is a small piece of heaven. She loves learning more about the life around her and the creatures that make the rainforest such a well-functioning ecosystem.

“Being in the rainforest gives me a sense of calm, reason and wholeness. It simply soothes my soul. I love interacting with people and sharing information about the importance of the rainforest, especially on some of the things we may not view as important such as wild pines, termites, vultures, ants, etc; explaining that everything has a role to play in the environment,” she said.