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 larv