The Formics (often referred to by humans as “Buggers”) are an alien, insect-like alien race that has been in a long standing conflict with the human species. The have a similarity to ants, and have a telepathic ability to communicate with each other making their sociology similar to bees.
There are two primary species of Buggers, the Queen and the Worker. The Queen is approximately three metres long and capable of producing eggs. When a new Queen egg is fertilized, a Worker gives its life in the process. A Worker is slightly less than one metre long and are controlled by the Queen. Due to this requirement for a Queen to coordinate all tasks, several queens exist that are spread across the planets and settlements.
It is because of this biology and society that conflicts with the humans began. From the perspective of the Buggers, they were merely killing workers when in fact they were killing independent humans. This is discovered towards the end of Ender’s Game.