Are chemicals produced by the body, such as the brain, and can change moods and actions and even resemble some recreational drugs.

serotonin

Explanation:

Recreational drug are drugs taken for enjoyment, or leisure purposes, they are drugs taken to altered state of emotions for pleasure, by changing the feelings, and emotions

examples are Alcohol, cigarette and cocaine

Serotonin is a chemical  induced in the human body due to drugs taken. It help regulate emotions, feelings, appetite and digestion, sleep, and memory.

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.