Brain slugs are an parasitic, invertebrate species native to the Brain Slug Planet. Brain slugs feed on cognitive energy in the form of the Alpha and Delta brainwaves. They attach themselves to their victims by using their adhesive slime to the scalp. The host's personality becomes totally supressed and their body is controlled by the slug. Brain slugs have a single, rudimentary eye that can only see the heat signatures of their prey, but they gain the use of their host's senses when they begin feeding. The slugs, as a species, are telepathically linked but prone to communicate with one another through their hosts.
Brain slugs are a fairly intelligent race. As primitive life forms they had a hard time establishing a society, but the assimilation of a DOOP survey crew allowed them to work together more effectively. Using their hosts' bodies, they set to work building a city with an important stop-over point on the way to many of the Universe's most popular tourist destinations. The spaceport the brain slugs built was a brilliant ploy to infest countless unknowing visitors on their vacations. The assimilated individuals return to their home planets and attempt to assimilate others by placing other slugs on their heads or convincing them to go to the brain slug homeworld.
The slugs will attack their hosts by crawling up their bodies until they reach the cranium. The only sure way to prevent infestation is to wear a helmet on the Brain Slug homeworld and use a garlic shampoo when in close proximity to an infested individual.