In the Classroom
They can be a nuisance but they are some of the most organised insects ever – some even keep livestock!
YOUR school is a lot like an ant colony – there are lots of people moving around but it’s organised and everyone knows what they should be doing. There are people – teachers – who keep everyone in line and the school has a leader, the principal. An ant colony is similar. Let’s take a closer look.
THE ANT FAMILY
You’ll probably have seen ants more than a few times in your life. They’re small and can be a nuisance – especially if you’re eating outdoors, or when they get into the dog’s bowl. But ants play an important role in the environment: they aerate soil, disperse seeds and eat pests such as ticks.
Ants belong to the family Formicidae (Latin for “ant”), which like bees and wasps belongs to the order Hymenoptera (from the ancient Greek word for “wing”). There are about 22 000 ant species on Earth, of which more than 12 500 have been classified (named and described). There are ants on every continent except
Antarctica. Some species such as the North American thief ant ( Solenopsis
molesta) are tiny – only 1 or 2mm long – and other tropical species such as the bullet ant ( Paraponera clavate) are enormous at up to 3cm long. Most species are between 5 and 15mm in length. All ants can bite, and some species can also sting (fire ant) or spray acid (red wood ant).
An ant starts its life in an egg. If the egg is fertilised, a female ant hatches. If the egg isn’t fertilised, the ant will be male. Ants undergo a complete metamorphosis, which means they pass through four phases: egg, larva,
pupa and adult. The queen lays the eggs from which larvae hatch after seven to 14 days. The larvae look like maggots and don’t have eyes. They can’t move much and are fed liquid food regurgitated by the worker ants.
After about a month the larvae enter the pupa stage. They start to look more like adults, but lie still with their legs and antennae folded against their bodies. They start out white and gradually become darker. After about six to 10 weeks the ant emerges fully grown.
They have a narrow “waist”, mandibles to chew, bite, dig and grasp things with, and antennae bent in the middle like a human elbow. The antennae (feelers) are sensitive to chemicals, movements in the air and vibrations. Ants also use their
antennae to communicate because they’re able to send and receive signals by touching.
Ants have glands that produce chemicals. These chemicals are used to convey messages or as a defence mechanism.
Ants leave a chemical trail (pheromones) on the soil wherever they go so other ants can follow. Ants that forage – move around looking for food – mark their route back to the colony with pheromones.
Other ants follow the route and leave behind more pheromones when they return to the colony with food. Once the food source is finished, the ants stop marking the route back to the nest and the chemical “trail” slowly disappears. Now you know how so many ants can find that piece of bread you dropped when you were picnicking.
Have you ever seen an anthill? It might look like a heap of sand, but inside it’s a well-organised network of tunnels and rooms in which ants live. Colonies can differ in size – one with 5 000 ants might consist of up to 100 underground rooms. The words “ant colony” not only refers to the nest, but also to the social hierarchy (the structure of the ant community) into which the ants are organised.
We call ants social insects because they live in large groups and work together
for the greater good of the colony. Each ant has its duties and each colony has groups of ants with specific duties. All the ants in a colony are of the same species (type) but they don’t all look the same as their bodies are adapted to their various duties.
A colony has at least one queen but sometimes there’ll be more than one. Her only purpose is to produce eggs. She’s larger than the other female ants and is usually the only one in the colony who lays eggs.
She has a large “staff” of female workers who take care of her. In fact, most ants in a colony are workers. Workers come in different sizes. The bigger ones also have larger mandibles that can deliver a painful bite. These bigger workers hunt and protect the colony – they’re called soldiers. Smaller workers are always building and maintaining the nest. They’re the ones who go out to forage for food and bring it back to the colony. They’re also the nannies to the larvae. Male ants have wings and their only purpose is to mate with the queen. At certain times in the summer months new queens and males are hatched in the colony. These ants have wings and leave the nest to start new colonies elsewhere. Male ants are usually smaller than females. Only males and queens have wings, but the queen removes her wings once the new colony has been established. The male ants mate with the queen in flight and then die.
STRUCTURE OF THE COLONY
Because there are thousands of different species of ants there are many different types of colonies. The structure of each colony depends on the nature of each species as well as their habitat.
The structures some people call anthills – those large, sturdy heaps of mud you find in the veld – are in fact not made by ants. These are termite heaps or mounds. And although termites are also called “white ants”, they aren’t scientifically classified as ants. Ants do create hills but these are mostly heaps of extra soil they’ve deposited from their excavations underground. But some such as the UK’s hairy wood ant ( Formica lugubris) build their nests above ground and cover it with plant material.
Ants also build underground nests under tree stumps, rocks or even concrete and paving, with only one tunnel opening above ground level. Then there are carpenter ants ( Camponotus) that make their nests in trees, chewing tunnels into the wood. Weaver ants ( Oecophylla) also live in trees and make their nests from leaves.
Cocktail ants ( Crematogaster) build nests from a paper-like substance they produce by chewing wood, then mixing it with their saliva to form a pulpy building material like papier-mâché that hardens over time. Army ants are an aggressive type of roaming ant. They’re nomadic and don’t have permanent nests like other ants do.
Leafcutter ants cut plant material and bring it back to their nests to cultivate the fungus they grow there. They also keep the fungus free from pests and mould. The fungus is then used to feed the larvae.
Other species such as the European yellow meadow ant ( Lasius flavus) keep livestock – aphids (plant lice). These ants protect the aphids from predators and in turn eat the honeydew (a sticky, nutritious liquid) that the aphids secrete. In this way, the aphids are almost like cows to the ants, who “milk” the aphids by stroking the lice with their antennae.
Some ants even go so far as to store the aphid eggs in their colony during winter and carry the newly hatched aphids back to the plants in spring. There, the aphids consume the plant juice and secrete honeydew for the ants to milk.
TEAMWORK Ants work together to get things done. They can use their bodies to form living structures, such as these army ants building a bridge to span a gap (above) or these fire ants that form a raft to float to safety during a flood in the Amazon (right). EXOSKELETON Like all insects, ants are invertebrates, which means they don’t have a spine. Instead they have an exoskeleton, a hard “shell” on the outside of their bodies that protects their insides. Their muscles are attached to this exoskeleton.
FARMERS An ant milks an aphid in her herd for its honey dew. Leafcutter ants harvest leaves to cultivate fungus that grows in their nests in fluffy white tufts. The ants then feed the fungus to the larvae.
2 3 HOME SWEET HOME 1 It may look like just a simple mound of soil, but it beneath lies an intricate underground city of rooms and tunnels, as this plaster cast of a nest (2) shows. 3 Weaver ants use larval silk (similar to what silkworms spin around their cocoons) to weave leaves into a shelter.
DEFENCE FORCE Red wood ants spray acid at their enemies to defend the nest.
Ants can carry up to 50 times their body weight!