Bombling

Bomblings are small, spider-like explosive creatures that grow out of the ground within the Forest Temple in The Legend of Zelda: Twilight Princess, and, later in the game, can be purchased and stored as a normal bomb. The item variety of this creature is very similar to the Bombchu. A player will immediately become acquainted with this variety of bomb, as he must use them to complete the Forest Temple. The bombling will crouch when approached and, if not picked up or attacked, will start a weak string of attacks upon Link that, over time, will cause accumulating damage.

These insects are invaluable within the Forest Temple because of their ability to become temporary bombs when startled. However, if these bomb insects are not picked up or destroyed within their "countdown" time span, they will self-destruct. On several occasions, Link will find the appearance of these bomb bugs very useful, as in some areas, blowing up a rock in the way is the only way to proceed to a new section of the dungeon.

The temple boss, Diababa, can only be successfully destroyed with the aid of these bomb bugs, along with the Gale Boomerang and a familiar monkey.

Image taken from Zelda Elements

Kakariko Bomb Shop
Eventually, in Kakariko Village, Barnes, the bomb salesman, receives stock of these specialty bombs that can be purchased and used outside of the Forest Temple area. The player will receive a letter after he completes the Lakebed Temple, indicating that the owner has stocked up on Bomblings. When used, these bombs will run in a straight line until they have contact with another object, at which point they will explode. 10 Bomblings can be held in each bag until Link receives the bomb bag upgrade, which allows him to hold 20 Bomblings per bomb bag. These bombs cannot be used underwater.