Several terrestrial arthropods such as insects, kilopods, diplopods, some ticks and some spiders, breathe through trachea.
The tracheas of insects are very thin conductive tubules. They originate from tiny holes, the spiracles, located in the lateral regions of the thorax and abdomen and ending in the cells. The contractions of body musculature act as bellows, pumping and expelling air from the tubules. Thus air enters with oxygen and exits with carbon dioxide.
The tracheas are directly in contact with the tissues. This means that in insects, the respiratory system functions independently of the circulatory system.