These enormous worms, found in Forsaken Cainhurst Castle, the Forbidden Woods, and the Nightmare of Mensis, are neothenic creatures (none of them have ever shown a traditional adult insectoid form), likely fly larvae which became Beasts themselves due to feeding upon contaminated corpses. They often burst out of the sacs of particularly large Bloodlickers and Silverbeasts (they probably squeeze their soft bodies in order to fit into the latter).
These beings are always found in groups and due to their extremely small size and speed, may often kill a hunter with lower health or many successive hits.
Making matters worse is that they are extremely resistant to most sources of damage but are very vulnerable to blunt damage. As such, it is wise to either use a blunt type of attack with a weapon you have or, ideally, use weapons that have many attacks with blunt damage such as the Kirkhammer (in hammer mode), the Beast Cutter (both modes deal blunt damage), the Amygdalan Arm (in club mode) or perhaps even the Tonitrus or Boom Hammer (as both always deal blunt damage in addition to another element).
It is very recommended to use the Beast Cutter though, as the strong attacks of the whip mode will allow players to kill these vermin from a safe distance.
- A Gigantic version of Parasite Larvae seems to be living inside of the headless variation of the Bloodletting Beast.
- Two larvae will erupt from the Silverbeasts in the Nightmare of Mensis when killed.
- The Parasite Larvae are quite the mysterious beings, they appear to crave blood and specifically target Beasts as their hosts. This is the case for the Silverbeasts and the monumental Bloodletting Beast that possesses a giant Parasite Larva for its head and shoots smaller larvae at its enemies.