Mantis-people are a race of altered humans created by Rick when he tried to cure the world of their "love" of Morty. They were later transformed into Cronenbergs again by Rick in yet another unsuccessful attempt at saving Earth.
Each Mantis-person were horrible disfigured; having the appearance of a huge mantis growing out from inside their previously human bodies and breaking through wherever there weren't any room inside the skin.
After Morty accidentally spread Rick's Love Potion airbourne throughout the entire planet, Rick fixed up a "cure" by mixing in praying mantis-DNA, which should counteract the potions effect because of female mantis' nature of killing their partner after mating. Rick spread this airbourne as well, and it did seem to work for a second, but quickly turned every human on Earth into disfigured mantis-people.
The mantis-people continued their search for Morty, attacking Jerry, Beth and Summer before Rick tried out another potion, this time made from koala, rattlesnake, chimpanzee, cactus, shark, golden retriever, and a tiny bit of dinosaur. This potion, however, turned all the mantis-people into Cronenbergs instead.
Mantis-people shared the "love" for Morty that they previously had as humans, but due to their mantis-DNA, they also wanted to eat Morty's head afterwards. They went on murderous rampages in order to find Morty and would fight among themselves over Morty.