The abdomen is the cone-shaped section of the butterfly's body. It extends beyond the legs, and houses the organs responsible for breathing.
Butterflies don't use active respiration organs like lungs, which require the animal to inhale a breath using specialized muscles. Instead, butterflies utilize a passive form of respiration, which requires no active participation of the butterfly. Passive respiration uses chemical processes to take in oxygen.
Spiracles are the mechanism through which butterflies take in oxygen and expel carbon dioxide. Spiracles are located along the length of the body, but mainly focused down the sides of the abdomen. Some spiracles are dedicated to taking in oxygen, while others are used to expel carbon dioxide.
Tracheal tubes are found throughout the butterfly's body, and they are responsible for diverting the oxygen to the different parts of the body. Since oxygen isn't transported through blood (as in animals with lungs), the tracheal tubes are the only way for oxygen taken in by the spiracles to reach the butterfly's body.