Giant mantises are mutated praying mantises created by the horticultural experiments that took place in Vault 22. They have since escaped from the vault and have spread into the Mojave Wasteland. Compared to other mutant creatures, their biological traits have remained relatively unchanged when compared with the original specimen, except for significantly increased size. They are still much smaller than humans, but make up for that by attacking in swarms whenever possible. Mantis eggs and mantis forelegs may be taken from their dead bodies.
Because of the height difference, giant mantises' attacks mainly consist of jumping and slicing its target in mid-air with their forelegs. If a mantis' antennae becomes crippled, it will become frenzied and the mantis will begin to attack anything within reach. There are quite a few mantises on the way to Jacobstown and around Spring Mt. Ranch State Park.
This variant is the standard giant mantis encountered later in the game around Spring Mt. Ranch State Park or on the way to Jacobstown. They can be found in groups or scattered around these areas when encountered. This variant is also the majority of mantises encountered in Vault 22.
Young giant mantis. They are much smaller and weaker than adult mantises. Some nymphs can be killed simply by walking over them. They are usually found early in the game at the Goodsprings schoolhouse and the Nevada Highway Patrol station, but they can also be found in Vault 11, Vault 22 and other areas.
Taking two or more mantis forelegs off of one will cause the model's forelegs to explode. This does not occur for mantis nymphs or giant Zion mantises.
Shooting a mantis ootheca will release a dozen giant mantis nymphs, which will then attack.
When observed for a time, a mantis can be seen cleaning its mouth. On occasion, it will flutter its wings the same way it would when attacking.
In Vault 22, research scientist Keely will mention that the mantises feed some of their prey to the vault's spore plants, but as they are "disinclined to eat ghoul meat," both groups of creatures had largely left her alone.
↑Courier: "What were you doing down in that cave?" Keely: "The mantises and spore plants virtually ignored me for most of the time that I've been here. It was only once I began to investigate the fifth level that my presence began to agitate them. I guess I was a little too close to home for them. A few days ago, I was attacked by a large number of mantises and was knocked unconscious. When I woke up, I was in that cave. The mantises seem to feed some of their prey to the plants. Fortunately for me, it appears the plants are disinclined to eat ghoul meat." (Keely's dialogue)