Metroid Database Bestiary

Exploding parasites that can embed their bodies in solid rock. Scarabs think nothing for themselves for the safety of their swarm. When a hostile life-form is sighted, they block its progress by embedding themselves in floors and walls. Embedded Scarabs violently self-destruct when threatened.

Scarabs travel in large swarms through narrow passages, and their loud skittering can be heard from far off. They will pause and embed themselves in the rock when Samus comes close. A single shot from any weapon will dispatch them, and the blast will often take out several at a time. However, don't get too close, or they will explode. A single Scarab will deal just a tiny amount of damage, but if you try to bulldoze through them, be prepared to lose a full Energy Tank.

Self-destructing does not seem like a viable survival tactic, even for an alien creature. Perhaps they reproduce very quickly and the skittering of the swarm warns off potential predators and prey.