Varkids are a special creature that resemble insects and can self-evolve into their stronger forms. They usually start out as Larval Varkids and if they are going to evolve, they burrow into the ground and reappear in a pod. Once they are finished, they will remerge into a stronger version, complete with full health and no status effects on them. It's important to note that each Varkid, at each stage, has a certain chance to evolve or not and there's also a time limit on them. This chance increases if there are more players in the game.
The weakest form of the Varkid, they can scratch/bite you, as well as leap/fly at you. Very easy to take out, as they are more annoying than troublesome.
The first evolution of the Larval Varkid, these will take to the skies and fly around, shooting acid projectiles at you. If they land, they can hit you with a melee strike that can do some damage, so watch out for this. If a Larval Varkid hasn't burrowed after 10 seconds, it will not evolve.
The second evolution of the Larval Varkid, they prefer to stay on the ground and keep up in your face. In addition to their melee strikes, they can also perform a charge attack that is difficult to dodge. They have more defense than the other stages of a Varkid, but they are weak against corrosive damage. If an Adult Varkid hasn't evolved after 20 seconds, you are free to kill it.
Super Badass Varkid
The next evolution of the Varkid, they are vulnerable to incendiary damage and step up their attacks from previous ones. Instead of a single projectile, they can fire up to eight at a time. If a Badass Varkid hasn't evolved after 30 seconds, it will not and you are free to kill it.
Ultimate Badass Varkid
The final evolution before the raid boss version, the Ultimate Badass is certainly one tough cookie. For one, they can spawn Varkids that track your position and explode when they are within a certain range. They can also utilize a spit attack, shooting three to four projectiles at a time. If a Super Badass hasn't evolved within 60 seconds, then it will not evolve at all.
Vermivorous the Invincible
First and foremost, Vermivorous cannot spawn in Normal Mode, so you need to be on TVHM or UVHM in order to fight it. It can only spawn from an Ultimate Badass, with there being a 7.5% for a single player and 12% for four players. If the Ultimate Badass hasn't evolved within two minutes, then it will never evolve and may be killed.
Vermivorous has more health than Terramorphous and is quite large, so you'll want a pretty open space, which will probably happen easily due to the two biggest Varkid populations being Caustic Caverns and Tundra Express - Farmhouse. As for attacks, it can summon the explosive Varkids that simply chase after you, stomp you if you get too close, and can shoot the acid projectiles like some other Varkids can do.