The commonest species that invades houses is the Black Garden Ant, which is actually very dark brown.
All ants have the main divisions of the body (head, thorax, abdomen) distinctly separated by very narrow waists and have a sharp elbow joint in their antennae. They are highly organised social insects. It is the foraging worker ants that invade buildings in search of food. These are from 3 to 5mm in length and are attracted to sweet foodstuffs which they take back to the nest to feed to the larvae and queen.
The so-called ants eggs sold for aquaria fish are actually the pupae. Flying ants are the reproductive males and females. These mating ants are winged and have a nuptial swarming flight during only a few days in July or August. Mating takes place in the air and the female then seeks out a nest site where she stays for the winter, laying eggs the following spring in order to start up a new colony.