The Omnomnom is the upgraded version of the Omnom. It is more powerful, and more aggressive. When feed greatly, it will pupate in to a Omnomnom Pupa and become an Omnomnom Beetle. They look like red and purple centipede.
In game descrition: "Hungrier and angrier than regular Omnom, these voracious animals can quickly devour their natural prey, the Slimemoss, in no time. Without Lizardman around to control them, this quickly leaves them starving and dying, never to omnomnom again. We can´t figure out if a Brain Bug is involved."
In game 2's discription: "A stronger type of Omnom. They might be able to defeat low level heroes. However, in a habitat where there are few to no Lizardmen, they tend to eat all thier food and end up dying out. Once they become pupae, they look just like sweet potatoes, so its pleasant to see some stupid, famished human heroes eat them by mistake. Their pupae are often used in Netherworld cuisines."