Ants are the dominant social insects and, numerically, the most abundant. At any one time, at least 1015 (one quadrillion) ants are alive on the planet! In general, ant colonies contain a variety of castes (groups of individuals with a common job) like workers or soldiers, plus a queen who is in charge of egg-laying. For example, the largest and most aggressive workers make up the soldier caste, whose job it is to protect the colony against dangerous invaders. Because of the way that sex is determined among ants, males are haploid (contain one set of chromosomes) while females are diploid (contain two sets of chromosomes). This causes a close interrelatedness among members of a colony and is theorized as one of the reasons for the evolution of social colonies.