Weakest link
While thinking about whether or not to Blood Layla, Quinn decided he would leave it to her and would ask her later. At a time when the sun wasn't out. If she became a vampire or something similar, she would have the same weakness as Quinn right now, and that wouldn't be good for the situation they were in.
Not all beasts were hostile, but the Teethworms were definitely that. The slightest vibrations would cause them to react, thinking food was nearby, springing upon its prey and attacking them. Although there were quite a few in number, they didn't have the hindsight to attack together.
Unlike like the Rattaclaws which were more difficult to deal with. The level of beast didn't generally mean how strong it was but how strong of a crystal was produced inside its body. There were some basic tiers stronger than others, and this was the same as you went up a tier.
Although it was unlikely a basic tier at any strength could match the weakest of an intermediate tier.