|The following is based on Fallout: Brotherhood of Steel and has not been confirmed by canon sources.|
Radbugs are the result of bugs being mutated by radiation.
They have an orb-like main body with a small head and six limbs with a claw on the end of each. When attacking, they leap forward and claw or bite a targeted creature. Apparently they have a set of human-like teeth, two fish-like eyes and an appendage somewhat resembling a tail.
This version exactly resembles the standard version of Radbug, but extremely small. Its damage is very low and requires a single shot to be killed. They often attack in groups of 5 to 10 to confuse the enemy due to their size and their speed.
Similar to the Radbug but smaller. A little stronger than the Mini Radbug but slower.
These are the most common variant of these critters. They are roughly the size of a dog and are stronger than both the mini and small versions.
Bigger versions of the standard Radbug, being the same size as brahmin. These pests are found near their home in the Vault-Tec Warehouse, guarding the Secret Vault and participating in battles between the super mutants and the Church of the Lost. They are fairly resistant and their attacks cause a lot of damage.
Mini Mutant Radbug
A Radbug mutated by the special version of FEV in the Secret Vault. They have a sort of web and spikes generated around their limbs and body and, more importantly, are protected by a green exoskeletal shell. While of a similar size to the Mini Radbug the Mini Mutant does damage comparable to that of the standard Radbug and is hard to kill. Five of these critters will appear whenever a Big Mutant Radbug is killed, as if from the bigger bug's corpse.
The same size as a Radbug, these mutated bugs have the same FEV-generated accoutrements and exoskeleton as the Mini Mutant Radbugs. They are very durable and do considerable damage, being able to kill even armoured targets in 4 or 5 shots.
Big Mutant Radbug
The same size as the Big Radbug and again having the FEV-generated mutations, these bugs are extremely durable and able to inflict even more damage than the Mutant Radbug. Additionally, whenever a Big Mutant Radbug is killed, five Mini Mutant Radbugs will emerge from its body.
All Radbugs appear only in Fallout: Brotherhood of Steel.