Laura Erickson's For the Birds

One of the most intriguing and satisfying sights I enjoyed in Costa Rica wasn’t a bird at all–it was a herd of insects. And not even insects that birds eat. I got a big kick out seeing ants.

I saw army ants only twice on my whole visit but boy were they fun to watch. These tiny predators are constantly on the move because they have no fixed home. Their battalions can be huge–one colony I saw marching along near Monteverde was still passing by in the same spot over an hour later!

When army ants are marching, insects, spiders, rodents, frogs, lizards, and other small creatures scatter in a frenzy. And the birds that eat these small creatures :frequently gather near the marching ants to snatch up the desperately fleeing creatures. Tropical America has a whole family of groups called antbirds that includes several species that spend virtually their entire lives following army ants. Antbirds are fascinating and varied. The Antpittas have just a tiny stump of a tail, very long legs, and a large, innocent-looking eyes, probably because they spend so much of their lives in the dark understory. Antthrushes have short wren-like tails that they cock up, and antbirds have a big blue tear-drop-shaped patch of bare skin around their eyes. Then there are antshrikes, antwrens, and antvireos–and all spend at least part of their lives following army ants for the food they scare up. Tanagers and other tropical species often join the flocks of antbirds-all in all there can be twenty or more species in a mixed flock moving about the rainforest when army ants are about.

If army ants were exciting to see, leaf-cutter ants were absolutely fascinating. These little ants chew leaves into tiny pieces and carry them back to their colony. They never eat the leaves—they simply grow a fungus on them, and then eat the fungus.

These leaf-cutter ants were everywhere in the rain forest, thousands walking along a narrow path, the ones headed back for the colony bearing leaves, the ones headed for the leaves going the opposite direction along the same path. These worker ants come in two sizes. Larger ones carry the pieces of leaves, and tiny ones ride on the leaves, chewing off the waxy coating so the fungus will grow more easily. I took a few photos of these curious creatures, which I put on my webpage–if you look closely, you can see the large hard-working ants lugging the leaves, and the tiny ants going along for the ride.

At one butterfly garden near Monteverde, there was a leaf-cutter ant colony on display, with the fungus that they culture from all those leaves on display under glass, the ants walking in and out through a little hole in the side. Like other ants, leaf-cutter ant bodies are laced with formic acid, making them taste bad to all but a very few birds. Their main enemies are anteaters, but I didn’t get to see any of them. I’m just as glad-these industrious little creatures were surprisingly endearing, and I found myself smiling every time I came upon a line of them. This little planet we live on sure has some lovely surprises.