Most insects have small holes in the exoskeleton called spiracles which open and close to regulate air flow. Insects do not have an advanced breathing mechanism like vertebrates. Instead they take in air and expel it though the small openings called spiracles. They are small holes which connect the internal respiratory system inside the insect with the outside world. Spiracles are surrounded by muscles which enable the insects to close and open them as necessary. Most insects have their spiracles mostly along their abdomen .