A beetle like pokemon with a blue exoskeleton its most notable feature is its larg pronged horn. Female heracross have a heart shaped horn and males have an 'X' shaped horn. They love to eat sap from inside trees and despite their great strength, size, and horn they are docile pokemon. They prefer to live in the deepest parts of forests, this is because there are many trees from them to feed off of sap. Due to their love of this delicacy, they have a special relationship with butterfree, as butterfree are not strong enough to break into the trees to get the sap themselves, so they share it with the heracross. 
 

Notable Heracross

Ash's Heracross 
He first appeared in the episode, 'A Sappy Ending', where a group of heracross and a group of pinsir were having territorial disputes, as Ash and his friends tried to find a solution for this dispute, one specific heracross followed him around until Team Rocket intervened, and eventually the two groups of pokemon were able to return to their respective parts of the forest, the dispute having been over. However, this heracross was still following Ash around, even after everything with the two species of pokemon had been resolved, and it then allowed Ash to capture it and add it to his own strong party of pokemon.