In the Class­room

They can be a nui­sance but they are some of the most or­gan­ised insects ever – some even keep live­stock!

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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).

METAMORPHO­SIS

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.

AP­PEAR­ANCE

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.

NAV­I­GA­TION

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.

THE COLONY

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.

SO­CIAL INSECTS

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.

FARMER ANTS

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.

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Ants can carry up to 50 times their body weight!

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