C. ANTS: Strength in Teamwork and Safety in Numbers

Harvester ants Anthills By carefully observing the size and shape of an ant nest hole and its surrounding area, you can often identify the species of ant that lives there. The harvester ant clears a large area near its nest hole. Bits of vegetation, seed hulls, and other debris will be scattered beyond the cleared area. Look closely near the nest for two distinctive Harvester ant body types-one with large muscular heads (for chewing up seeds) and one with more normal-sized heads. Harvester ants often run about with the abdomen tucked under the body, so it looks like half an ant. Fungus-growing ants can be identified by their crescent-shaped pile of loose, usually yellow sand that forms a "c" around the nest entrance. The ants pile the sand on the downhill side where it won't wash back into the burrow during a rainstorm. The cone ant forms a volcano-shaped nest entrance. Two species of cone ants are found in Florida scrub and nowhere else. Commonly found in scrub, the nests of the fungus-growing ant can be identified by the pile of loose, sometimes yellow sand it distributes in crescent-shape around the burrow entrance. Inside the nest is a "fungus garden" that the ants create by chewing up plant matter, spitting it out, and embedding it with spores of certain fungi. Sometimes caterpillar droppings are collected and used as fertilizer. Ants must weed out any alien fungi and bacteria (which could wipe out their crop), and must ventilate the growing chamber to maintain correct moisture and temperature. When new queens fly away to mate and start a new colony, they carry a supply of delicious fungus with them! The fire ant creates a nest with loose sand piled high and scattered with holes. Not all animals feel fire ant bites and stings as we do. Armadillos, also an exotic species, can be seen digging in fire ant nests, covered head to toe with angry insects, yet rarely seem to notice!

Introduction

As you saw in Unit One, sand is an ideal construction material for small burrowing animals. This section builds on that theme by focusing on ants--which are among the most abundant insects of Florida scrub and other sandy habitats of Florida. During the ant activities included, students will have the opportunity to use observation skills developed in the tracks section. Instead of identifying animal tracks, students will try to identify species of ants by observing characteristics of their anthills. The ant section will also be important for understanding the next section, Life in the Leaf Litter Layer.

The specific goals of this section are to introduce students to the concepts of animal sociality and animal communication. Ants beautifully demonstrate these two subjects because they are simultaneously very complex insects and incredibly limited in their behavior. While ants are dominant insects of Florida scrub habitat, they are just as dominant in most other terrestrial habitats in Florida. Therefore, students can apply ideas from this section to the ant behaviors they see in their own backyards.

Because humans and ants are both social animals with advanced communication systems, the problems and benefits of being social are usually easy for students to understand. You can take advantage of this intuitive understanding when helping students formulate their own hypotheses. At the same time, our culture presents very misleading views of insect social systems. Ants offer a good opportunity to discuss how different the media presentation of insects can be from the scientific facts.

This section also deals with observing and measuring, with consideration of experimental method in designing projects. Other less prominent themes are complete metamorphosis, animal defense, and the importance of genetic relatedness in the structuring of social systems.

Background Information

Ants are everywhere! Their nests can be found in the ground, in trees, in grass stems, at the beach, on mountaintops, in wet areas, and in the desert. Some ants are most active when it's hot, others prefer chilly weather. Ants have some impressive abilities. Some ants grow their own food underground and others have big muscular heads for grinding seeds and blocking nest entrances. Some ants have snap-trap jaws that can cut the head off most any insect! And some ants can find that one little crumb on the kitchen counter!

Florida could claim to be the "Ant State" of the eastern United States because our state has the largest number of species (around 220). Ants are also major players in Florida's ecology. The imported fire ant is the best-known species, but other ants are equally influential. Many of our native ants are important predators that help control populations of other insects. Because of their abundance, ants are readily available food for a large number of animals, including tree frogs, lizards, and many birds, especially woodpeckers.

Florida scrub is home to over 50 species of ants (approximately 9,500 species have been discovered in the world so far). Two species of ants are endemic to scrub-and can be found nowhere else. Some ant species live in hollow twigs and grass stems, but a great majority live in the ground. The sandy soil is crisscrossed with a seemingly unlimited number of underground ant tunnels. Some species dig nests as deep as 3 meters (or about 9-10 ft.) while others have tunnels and chambers just under the surface.

In some ways, a colony of ants appears to be organized like a human community with workers doing different tasks, but uniting for big construction projects and to defend the nest. The advantages of this social system are sort of like those in our own communities. Ants, like humans, benefit from both group efforts and individual specialization. The disadvantages are also similar:

1. The colony requires large amounts of resources, which must be imported, just as food must be imported into a city. Foraging outside the nest is often dangerous for the workers.
   
   
2. Since the colony requires large quantities of food, ants are not able to be as specialized and efficient as a species that requires a smaller supply of food. For example, there is no ant in the scrub that lives on acorns, while there are several species of acorn weevils (beetles) that are specialized for eating acorns and are able to deal with the defensive chemicals found in acorns.
   
   
3. The concentration of ants in their colonies makes them vulnerable to specialized insects, birds, and mammals that feed on ants.

In one way an ant colony is not at all like a human community. An ant colony is a family. The queen is the mother of all the workers, who are therefore sisters. The workers don't produce their own young, but instead raise their own siblings. When ant colonies become large, they can produce males and new queens. Males and queens have wings and eventually leave the colony--usually in a mass emergence that is synchronized with the flights of males and queens from other colonies.

Mating normally occurs between males and queens from different colonies. A winged, reproductive female, or queen, is fertilized by a short-lived winged male during or after a brief flight. Ant flights often occur after a rain, when the big, soft-bodied queens are less likely to dry out. After mating, the male dies. The queen lands, sheds her wings, and digs a tunnel into the sand to establish her nest. Using the energy gained from breaking down nutrients from her now useless wing muscles, the queen begins to lay eggs.

Living from 5 to 15 years, the queen can lay fertilized eggs throughout her life. (The queen mates only once, but can store sperm.) Within 2 ½ to 3 months, the eggs develop into larvae and the larvae into infertile, wingless females called workers. Depending on the species, the queen will break down wing muscle and use the nutrients to feed her larvae or she will come to the surface to forage. Once the larvae develop into workers, they take over the job of digging a larger underground nest and caring for the queen. As the colony grows and the nest becomes larger, more workers are produced. Although the queen produces an enormous number of workers for the colony, some ant species will capture eggs and larvae from neighboring nests and raise them as slaves. If the queen dies, the entire colony would eventually die, too.

Life in the ant colony isn't easy. First, the home must be clean. Bits and pieces of dead workers must be removed. The nest must be kept free of molds, mildews, and fungus that can kill both the ants and their larvae. An acid in ant saliva keeps dangerous microorganisms from spreading and multiplying. Second, food must be found and prepared for the "family." Ants have a crop (a pouch-like organ where food is softened and stored) and can save partially digested food that can be fed to other ants. Third, the home boundaries need to be constantly defended from other territorial ants and nest parasites. Fourth, the eggs and helpless larvae must be cared for in the nursery. The larvae are fed solid food such as pieces of dead insects and food regurgitated from the crop. They are also licked clean by the workers. And, finally, the queen must be fed and cleaned.

Digging and maintaining the nest is tough work. Ants do not have specialized digging feet, but carry the sand in their mouths or under their chins with the help of a loose basket of hairs. If the nest gets too hot, workers dig more horizontal side tunnels to increase the airflow. If the nest gets too dry, workers dig deeper tunnels to find moisture. Some ant species can be identified by their nest entrances.

Because ants have so much work to accomplish, they need effective ways to communicate with each other. Ants use special communication chemicals, called pheromones to send alarm signals, create scent trails to a food source, recruit help from colony members, recognize each other, identify the young that need to be fed, and determine who their enemies are. Ants also communicate in physical ways. Some kinds of ants beg for regurgitated food by tapping antennae with a fellow worker. Other kinds of ants can make a squeaking noise by rubbing parts of their abdomen together.

Different species of ants have different food preferences. Some ants are carnivorous, while others are herbivores and eat only plant material. Some ants are specialists and eat only insect eggs, others feed on fungus they grow themselves, while other species will eat just about anything, including dead insects and plant nectar.

Sometimes other invertebrates, such as beetles, cockroaches, flies, and other ant species, will disguise themselves by using a colony's chemical language and invade an ant nest. These social parasites, which often look nothing like an ant, can live in a thriving ant nest without being recognized as an imposter! Once inside the nest, these predators prey on the ant eggs and larvae while being cared for by the workers! What a life!

Ants defend themselves by tasting bad (formic acid), by biting and stinging, and by fighting. One species of carpenter ants defends its nest entrance by blocking the opening with its big, cork-shaped, hard head. The imported fire ant is especially well known for defending itself with its double-whammy sting and bite!

The Nasty Non-Native

First seen in Alabama in the 1940s, fire ants are an exotic (non-native) species accidentally introduced to the U.S. from the flood plains of Brazil. They are adapted to seasonally flooded, grassy areas, so do not thrive in dry scrub as well as in other habitats. However, they can be found in lower, slightly wetter areas adjacent to scrub and in lawns. If a nest area floods, fire ants can form a clump by grasping onto each other and floating until they hit safety-a clump of grass stems, high ground, etc. When waters recede, the ants rebuild their shallow nest.

While shallow nests are important to fire ant survival, the location means the nest is easily disturbed. If you quickly swipe your foot over the top of the mound, you can expose the nest, workers, nursery area, and queen. Because their nests are so vulnerable, fire ants are very aggressive. In response to a disturbance, some of the frenzied workers will boil out of the tunnels in an attempt to find the invader. A chemical signal tells workers when to sting and bite (in unison). Meanwhile, other workers attempt to carry the eggs and larvae to safety.