A Pineco hangs from a tree branch and waits for prey. While eating, if it is disturbed by someone shaking its tree, it falls on the ground and suddenly explodes.
(From Bulbapedia)Pineco is a blue-green, pinecone-like Pokémon with red eyes and no visible limbs. It has a single spike on top of its head, which is supposedly its stem. It makes its shell thicker by gluing tree bark to its body. The glue is made of fluid that Pineco spits out, which hardens when it is exposed to air. Unbothered by the added weight of its shell, it patiently hangs from a tree branch to wait for flying insect prey. In Alola, its favorite prey is Cutiefly. Typically immobile, it will drop to the ground and explode if someone shakes its tree while it is eating.
(From Bulbapedia)Pineco is based on a bagworm living in a pine cone. Its metallic appearance and ability to explode also links to a hand grenade. In addition to its possible relation to weaponry, its ability to learn Spikes may be a reference to caltrops.
(From Bulbapedia) Pineco is a shortening of pine cone, reflecting its pine cone-like appearance.