Ants belong to Family Formicidae within Order Hymenoptera the group of insects that includes ants, bees, wasps, sawflies and wood wasps. In Australia, about 3000 species of ants are known.
Ants are social insects that live in more or less permanent nests. Colony sizes vary enormously and are mostly located in soil, wood and among rocks. In relation to their feeding habits, ants may be predators, perhaps with specific prey (eg termites), or scavengers, which again may have a specific diet (eg the honeydew or sugary excretions of plant-sucking bugs) or a general one. The latter types may be almost omnivorous; that is, ants for which almost any type of food is acceptable. Being very common intruders in and around buildings, ants tend to be very familiar insects. They are commonly observed around foundations and in walls, roof voids, kitchens, lawns and gardens, the wood of decaying trees, and rockeries. As a group, ants are considered by many to be among the most successful of allinsects.
Structure
Typically, ants have three clearly defined body segments: head, thorax and abdomen. In most, the first one or two anterior abdominal segments (which connect with the thorax) are much smaller than the rest, producing a distinctly 'waisted' appearance. These smaller basal abdominal segments, known as the pedicel, usually have one or two projections called nodes, which may serve as important features in identification. The head carries compound eyes, elbowed antennae and sometimes ocelli. When present, wings are membranous, and forewings tend to be broader and longer than hindwings.
Life cycle
Individual ants undergo a complete metamorphosis during their development. Eggs are mostly small and ovoid in shape. The larva that hatches out is a whitish grub that is narrower towards the head. The larvae are fed by the adults and after sufficient feeding and several moults, the larva pupates. The pupa is similar in shape to the adult but is usually soft, creamy-white and inactive. In some species the pupa is protected with-in a silk cocoon. Eventually the adult emerges, and a few hours or perhaps even days may be required for the process of cuticle- hardening and darkening The development from egg stage to adulthood may require from 6 weeks up to very long periods, depending on the species concerned, food availability, temperature, season and a range of otherfactors.
There are three castes of ants:
- Male - Adult males are winged. Their specific function is to mate with thefemale.
- Female - This caste is usually the largest in body size. The female begins adult life as a winged insect, but the wings are dropped soon after mating Normally the female mates only once,andshewillcareforthefirstyoungSomeantspecieshaveonlyonefemalereproductive( `queen'), while others may have many. Typically, females may live for up to 15 years.
- Worker - This caste comprises sterile wingless females. They are the most numerous castes, serving the colony by nest-building, foraging for food, feeding immature ants and other castes, caring for eggs, defence and so on. In some species there are different kinds of workers. Large workers with well-developed heads are sometimes called soldiers. Workers mostly live for about 1year.
The female or 'queen regulates the colony. After one mating with a male (after which the male usually dies), the female commences egg-laying. Those eggs which are fertilized become females (mostly workers), and those eggs which are not fertilized develop into males. At certain times of the year large numbers of winged males and reproductive females are produced. These usually swarm in a colonising flight, during which mating on the wing usually occurs. The male dies soon after. The female, if successful, will drop her wings and find an appropriate nesting site in which to start a newcolony.
Some ant species seldom swarm. Instead, these ants may mate within the nest, eliminating the male afterwards and developing numbers of female reproductive. Some females, having been fertilized within the original nest, may, with numbers of workers, leave to form a new colony. This method of colony formation, sometimes called 'budding-off', seems important in the Argentine ant and Pharaoh's ant.
Habits
Most ants live in more or less permanent nests, but in adverse conditions a change of nest location is not uncommon. Typically, worker ants forage from the nest for food. Many do this by travelling in fairly well-defined trails, once a food source has been established. Methods employed in trail marking may include reference to landmarks, orientation with respect to light and, very commonly, the laying down of 'scent trails' in the form of trail-marking pheromone secretions. More generally, orientation and communication in ants may rely on smell (as in trail- markingoralarmpheromones),taste(asinfoodexchangebyregurgitation),hearing(asmaybe the case with tapping and stridulation), touch (as in antennal stroking), or sight (in ants with well-developed eyes).
In their feeding habits ants tend to be predators or scavengers with a wide range of specificity. Some predatory species are very specific (eg preying only on termites), while others are general predators. A very common scavenging habit is the attendance of plant-sucking bugs on plants. Here, ants consume honeydew and, sometimes, in exchange for this food, they will protect the often fairly sedentary plant suckers from predators. Several species of ants are almost omnivorous scavengers, consuming a very wide range of animal or plant products. It is these scavengers that have most successfully exploited people'sdwellings.
Why ants are considered pests
Ants are often regarded as 'nuisance' pests in and around buildings. Small mounds resulting from their excavations may be considered unsightly along garden paths, on balconies, and around skirting boards and architrave bases. Occasionally, such excavations under paths may be sufficiently extensive as to cause cracks in older paths. Trailing of the ants themselves, in and around buildings, is considered unsightly by many. Where plants are grown, ants may attack and damage or consume seeds and seedlings. Swarming may occur within premises, and this may prove particularly disturbing to occupants. As well as general 'nuisance aspects, ants max present a health risk. There are known instances of ants mechanically carrying, on their bodies or in their digestive tract, disease organisms causing dysentery, smallpox and a variety of pathogenic bacteria, including Salmonella. As ants commonly scavenge in kitchens and other food-handling areas, as well as in garbage cans, dog excrement and other possible sources of disease organisms, their potential for transmitting diseases to humans should not be overlooked. Such a threat to health can be very serious in the case of severe infestations in hospitals. In addition to the health threat posed and nuisance aspects, some ants may bite or sting humans. Table 11.3 describes the appearance and nesting and feeding habits of commonly occurring ants, including pest species.