Before the Great War, European mantises could be found in southern Europe, all over the northeastern United States and Canada to the Pacific Northwest and ranged from 5 cm to 7.5 cm. After the Great War, two divergent mutation can be seen. The variant seen in California come from tandem exposure to radiation and Forced Evolutionary Virus while the other variant seen in the Mojave Wasteland are created by the horticultural experiments of Vault 22.
The mantis is a mutated insect that tends to come in large groups. They can pose a major threat if they surround you.
↑Fallout Bible 0: "6. According to Chris A., the ghouls in V12 were exposed to radiation and FEV. I know Harold said the Vault door opened early or something, so the radiation bit makes sense. My question is, how were the ghouls of Vault 12 exposed to FEV? Harold was a special case, since he went to the Vats with... er... someone, whose shall remain nameless... and got dipped. How do you account for the others? - Richard Grey" "When the West Tek research facility was hit, it shattered the FEV storage tanks on levels four and five and released the FEV into the atmosphere. Through some means, perhaps propelled by the explosion, the virus was able to reach the ghouls quickly and the mutation process began even as the radiation was rotting away their bodies. How the virus was able to survive the blast without being sterilized is unknown... it would depend on what type of warhead cracked the West Tek facility like an egg. Actually, Harold never said he got dipped (although it's possible). He was exposed, however - being in close proximity to FEV is enough to cause mutations, as the Enclave slaves mining Mariposa discovered. I imagine the shield between the vats and the control room in Mariposa was meant to keep the virus contained." Note: The West Tek Research Facility is an underground bunker, which although was directly hit by a nuclear weapon did not release the Forced Evolutionary Virus. The FEV was moved to the Mariposa Military Base (a bunker under a mountain) before the Great War.
↑Fallout Bible 0 Answer me these questions three: "2. Does FEV really cause sterility? In Fallout 1 it seemed like the answer was a resounding yes, and a number of reasons for this were given by Zax and Vree. But then in Fallout 2 after you take Marcus to the Cat's Paw he says "I hope she doesn't get pregnant" and says that the FEV doesn't make mutants go sterile, it just makes it take a few years "to get the juices flowing again". Moreoever, the deathclaws in Vault 13 were infected with FEV and yet they are able to reproduce. So, does the FEV cause sterility or not?" "Answer:" "FEV causes sterility in some creatures. FEV does cause sterility in super mutants and ghouls - Marcus' comment in New Reno was a joke only (and it was an inappropriate one, for which I apologize for). For other creatures, however, the FEV does not cause sterility - in fact, it may actually speed up their reproductive cycles (in tandem with potential drawbacks). Known species that can reproduce after being mutated with the FEV include most species of rats, the mantises (who are known to have bred so fast they cover the Salt Lake City area like blankets), the radscorpions, and the deathclaws. This is only a partial list." "3. Are the radscorpions a product of the FEV virus? When you talk to the doctor, Razlo, in Shady Sands, he tells you that they were once American Emperor Scorpions but that he has no idea how they mutated because radiation alone couldn't have done it. For that matter, what about all of the other creatures of the wasteland? Which ones have been mutated by FEV and which ones haven't? Maybe in the bestiary each creature could have a stat that shows it's level of FEV infection." "Answer:" "The radscorpions are a result of a combination of radiation and the FEV virus, and Razlo in Shady Sands is correct - they were originally Emperor Scorpions that have grown... big." "FEV-Infected Critters in the wasteland include almost all the ones you've seen in F1 and F2:" "Mantises." "Most species of rats." "Gecko lizards." "Brahmin" "Scorpions" "Ants" "Various varieties of plants, including the Venus Flytrap." "Rumor has it some dogs were affected, but no one's seen any, so for now that's just rumor. Of course, the centaurs are a mash of human, dog, and various other parts... but hey, who knows how that mutation came about. Grey was probably messing around in one of his labs."