Lasius niger colony in the base of a plant pot (video: Steve Head)
Worker ants mostly gather food in the form of other insects that are carried back to the nest. Tetramorium caespitum eats seeds, mainly of grasses and heather, which it will gather as a food store in the nest. Other ants also gather certain seeds, such those of violets and gorse, which have oil-rich attachments. Sweet liquids, such as fruit juices and honeydew excreted by aphids, also form an important part of the diet. Ants that have found a good food source will lay down a scent trail so other ants from the nest can locate it.
When threatened, ants will defend themselves and their nests. Worker ants have a sting that will inject poison into the body of an enemy. Some ants, such as the wood ant Formica rufa, can squirt formic acid at their foes. When a nest is under threat, worker ants release an alarm scent or pheromone that rapidly alerts other worker ants to the need to defend the nest.
At certain times of the year, the queen ant will lay eggs that will produce either male ants or young queens. These ants have wings and when conditions are right, the males and young queens emerge from the nest and go off on mating flights. Mating flights in some ant species are triggered by warm humid weather, which can result in simultaneous mass emergences from many nests. After they have been mated, the young queens break off their wings and seek suitable places to establish new nests.
Queen ants lay eggs that hatch into white legless larvae, which are fed with food regurgitated by the worker ants. Unfertilised eggs will produce larvae that develop into male ants. Fertilised eggs will develop into worker ants or young queens, with the latter being fed a richer diet when at the larval stage.
When fully fed, the larvae turn into pupae and later emerge as adult ants. In some species, the pupae are exposed but in others the larva spins a silk cocoon around itself before pupating. These whitish brown cocoons are often mistakenly referred to as ant eggs; real ant eggs are too small to be easily seen.
Role of ants in gardens
Ants rarely cause any significant direct damage to plants. However, they are often regarded as a nuisance in gardens, especially when their nest building activities produce heaps of excavated soil on lawns, or partially bury low-growing plants in the flower beds.
Ants often visit aphids on plants to collect the sweet honeydew that these sap-sucking insects excrete. Aphid predators, such as ladybirds, are likely to be driven off by ants attending the aphids, so aphid infestations may develop more rapidly in the presence of ants. Ants themselves are the prey of many other insects and spiders. Birds such as house martins, swifts and swallows have a feeding bonanza when ant mating fights are taking place.