All this Monster is called the Destroyer Serpent. Those monsters destroy everything with their poison and because of this, they got this name. Every one of the Monsters already reaches the intermediate Epic grade. But the problem was that their poison could easily affect a peak Epic grade or Early Planetary grade warrior. With that, you can imagine how powerful those Monsters are and how dangerous they are.
Right now as you can see every warrior maintains a safe distance, but those Monsters did not stay ideal and the approach toward those human Warriors. At the same time, they were still using their attack on those Warriors. On the other hand, those Warriors also did not stay ideal.
All of them also know that those monsters will try to get close to them so that they could affect them but unfortunately for those Monsters, they weren't that fast enough. Most likely because of that enormous body they are unable to react on time.