Radroach

Great American cockroaches, colloquially called radroaches or simply giant cockroaches, are giant versions of the original cockroach species mutated by atomic radiation.

General characteristics
Found mainly in underground areas and sewers across North America, these creatures can usually be found in fairly large groups. They feed on the dead, but will go after living creatures if isolated. Their numbers are usually their greatest advantage. Radroaches live mostly in the areas east of California.

It is said that radroach guts are actually useful in the treatment of radiation poisoning, and are widely used by tribals for that purpose.

Capital Wasteland
Radroaches in the Capital Wasteland look similar to real-life cockroaches. The mutations they have undergone include massively increased size, and now they are about as large as house cats.

Radroaches are not normally aggressive if the PC keeps his distance. They will attack, however, if the player seems to threaten them, either by having a weapon drawn, invading their territory, battling another enemy nearby (which is limited to less than a foot around the creature), or attacking them directly. Generally, they will spread their wings in warning when they're about to attack. Companions will attack them even when they don't attack or provoke the player.

Two named radroaches appear in Fallout 3: Fluffy and Jitters.

Fallout 3 features a unique Unarmed V.A.T.S. animation when killing radroaches: a boot stomp followed by a victorious boot grind.

Midwest
In the Midwest, radroaches are a common sight in the Wasteland. As in the Capital Wasteland, they can be encountered nearly everywhere, from old buildings to plains. However, they are drastically different and more dangerous than those met in the Capital Wasteland. They have a big, protected main body and small legs, and their saliva is incredibly toxic. They are very aggressive and attack every human unlucky enough to encounter them.

The Midwestern radroaches are more varied than their Capital Wasteland cousins. Three variations are known:

Small radroach
The weakest of the radroaches, they can easily be killed. However, their bites can poison an opponent, and when they are in large groups, they can kill even a prepared combatant. Small radroaches are nearly the same size as their relatives in the Capital Wasteland.

Large radroach
Similar to their smaller cousins, they are, however, larger (being approximately the same weight as a human) and have an ability to spit their toxic saliva.

Roachor
Roachor is a unique mutant radroach encountered by the Warrior of Midwestern Brotherhood of Steel. He is an "advanced" version of a large radroach, who lived in the Peoria facility. It appears Roachor was affected by the high amount of radiation coming from a strange production device which was used in manufacturing fission batteries. He is even bigger than any large radroach, being the same size as a car, his body glowing with a greenish radioactivity. His poison is even deadlier than that of Midwestern radroaches. However, the Warrior succeeds in killing him.

Appearances
Radroaches appear in Fallout 3, Fallout: New Vegas and Fallout Tactics, and were to appear in Van Buren. They were also mentioned in Fallout Bible 1.

Behind the scenes

 * In real life, roaches are noted for their relatively high resistance to radiation--about five to six times that of humans. However, there are other insects and arachnids even more resistant to radiation, including fruit flies and scorpions.
 * The radroach's GECK id is AdamsMorganRoach. Adams Morgan is a district of Washington DC.