Might of the termites
They may be pests to you, but on Africa's grasslands they improve the soil, provide lookouts for cheetahs - and make a tasty snack
It's party time on the savanna! Right about now, millions of winged termites are taking to the air. It's the same every year: They fly around for a few minutes, land, pair off, mate, and begin digging a new colony of termites.
Termites aren't the only ones celebrating. So are the local wildlife - and people.
"The sky is black with thousands of black kites coming in to feast on the termites," says Scott Turner, an associate professor of biology at the State University of New York. Dr. Turner has studied African termites for 20 years. He never tires of seeing the flight of the termite mating swarms.
Bat-eared foxes, serval cats, and mongooses pounce on termites as they land. Hyenas, aardwolves, and aardvarks lick them up off the ground in heaps. The local people gather them up and fry them on coals or hot skillets. They are considered a delicacy.
The season is special because only mating termites fly. Most termites can't breed.
There are four types of termites: the queen and king, and the blind workers and soldiers. "The queen is literally an egg-laying machine," Turner says. She lays one egg every three seconds, on average. The queen grows to be about two inches long, but most of her length is a vastly swollen abdomen. She and the king stay in the "queen's chamber" of the termite mound all of their lives. Worker termites take care of the royal couple's every need. Soldier termites, with large jaws strong enough to draw blood from a finger, protect the nest.
Termite mounds continue as long as the queen lives, from four to 12 years. "Mounds are not abandoned like bees' nests might be," Turner says. When the queen dies, the colony itself dies slowly over a period of months as worker termites are not replaced. (Workers live only a few months.) The mound disintegrates.
Each year's crop of winged termites, male and female, are the potential queens and kings for new colonies. They all have a large store of fat to tide them over until they can produce workers to feed them. "This fat is what makes them a tremendous treat," Turner says.
These termites aren't the pesky wood-eating ones feared by homeowners. This large, hardy termite species of the tropical grasslands doesn't live in wood. Instead, they build a home using their saliva and excrement to bind soil into tall nests or mounds. The average mound is six or seven feet, but some are as high as 20 feet.
This particular termite (Macrotermitinae) is the architect of the creature world. The world's tallest nonhuman structures are built by these large termites. If a termite were the size of a human, their mounds would be 180 stories tall (2,000 feet).
The high-rise termite mound isn't an apartment building, though. The termite colony lives more than 10 feet underground. The tall mounds act as air conditioners and ventilators, circulating air for the colony below. Winds blowing across the mound create a difference in pressure that pulls air through the network of tunnels built by the termites. Turner likes to think of the mound as a lung, and the wind as the muscle that enables the breathing.
The word "termite" comes from the Latin word tarmes, meaning a small worm that makes holes in wood. Termites have been on Earth for more than 50 million years. More than 1,900 species are widely distributed through the world, though most are found in the tropics.
Turner researches the Macrotermitinae termite in northern Namibia in Africa. There, termites make up one-half of the biomass on the savanna. "Biomass" means all the living organisms - animals, plants, bacteria, everything. Half of it is termites - think of it! Termite mounds are found on tropical grasslands worldwide. In fact, there are more termite mounds in Brazil than anywhere else. This is a good thing, because termites are the backbone of the savanna ecosystem.
Anteaters, armadillos, bat-eared foxes, aardwolves, aardvarks, and mongooses eat termites yearround. They all have large ears so they can listen for the insects moving around underground. Ground squirrels, mongooses, and meerkats even live in abandoned termite mounds. Leopards, cheetahs, and other hunters use the tall mounds as lookouts to spot game. Termite mounds are sometimes the highest points on the savanna.
Savanna monitor lizards (they can grow to be five feet long) dig into mounds to lay their eggs. Elephants sometimes use mounds as scratching posts!
But even more important than this, termites replenish the soil. The insects in a single termite mound eat about as much plant material as one head of cattle, Turner says. But because these termites add nutrients to the soil at such great rates, they actually increase the productivity in the communities they inhabit. So for cattle ranchers, termite mounds are a good sign, even though cows and termites would seem to compete for grass and plants.
Humans can't digest grass, stems, or other plant parts containing cellulose. Cows, antelopes, elephants, American termites, and other creatures have helpful microbes in special digestive systems to help them break down cellulose and extract nourishment from it. Mound-building termites in Africa have another way: They farm fungus.
The fungi that termites grow is similar to the mold that grows on rotting food. Termites feed grass to the mold, which breaks down the cellulose for them. Then the termites chow down.
The fungi work fast. The high-energy food that results helps African termites grow to be two or three times as big as their North American cousins. It also means that the queen can produce more eggs. Each mound may contain more than a million workers, compared with 10,000 to 100,000 per colony for other termite species.
After the dead plant material is decomposed in the fungus garden and the insects have eaten what they need, workers carry the nutrient-filled waste up to the surface of the mound, where it washes back onto the soil. In this way, a termite mound creates 35 cubic feet of enriched soil every year.
In wet areas and in wet seasons, fungi, earthworms, bacteria, and beetle larvae help decompose plant and animal matter and so enrich the soil. But when the climate is dry, as on the savanna, termites are the primary decomposers.
And they do a great job! Termite mounds may contain up to 60 tons of soil materials, Turner says. And since the mounds tend to be in places where soils are least fertile, the mounds boost soil fertility considerably as they decompose. Australian scientists think that the good topsoil in northern Australia is largely the result of several thousand years of termite activity.
So while termites may be unwelcome in American homes, they are the unsung heroes of the tropical savannas.
Some of the fastest, largest, and most ferocious land creatures on the planet live on the African savanna. Lions, cheetahs, and elephants call tropical grasslands home.
But despite the animals' size and fierceness, grass is king here. All wildlife depends on it, from tiny soil microbes to the strongest hunter. It is the primary vegetation for miles.
Grasslands lie at the heart of every continent except Antarctica. They are vast, open, treeless spaces where little grows taller than the tallest blade of grass. Harsh weather conditions, poor soil, grazing animals, and fires keep trees and woody shrubs from growing.
Temperate grasslands, like the Great Plains in the United States, grow in particular bands of latitude above and below the equator. Tropical grasslands grow near the equator. Savannas thrive in Africa, Asia, Australia, and South America.
Savannas have only two seasons: rainy and dry. The rainy season can last from seven to nine months. Twenty to 60 inches of rain might fall. But in the dry season, only an inch may fall. As a result, tropical grasslands explode in flames almost every year. Fires usually occur just before the rainy season starts, when grass is very dry and clouds bring lightning but no rain. A fire may burn for weeks before the rains extinguish it.
Fire replenishes the soil. Dead leaves, stems, and flowers contain nutrients needed for new plants to grow. Fire decomposes this material instantly, returning nutrients to the soil in the form of ash.
Grass endures. Everything about a grass plant makes it the perfect savanna survivor: its root system, leaf shape, and method of growing.
A grass plant is 90 percent roots. Elephant grasses, for example, may grow more than 10 feet tall, but their roots stretch at least that deep. The roots absorb water and nutrients and store food. The stored food allows a plant to regrow if its leaves are consumed by drought or fire. Unlike a tree, which grows from the tips of its branches, grass grows from the point where stem and roots meet.
The narrow shape of the grass leaf helps keep the plant alive during the dry season. The leaf's narrow surface area helps conserve water lost through evaporation. Grasses don't need broad leaves because they are in sunlight all day - no trees, remember?
On the savanna, grass rules.