Question

Are there any aquatic insects? Do they breathe through a spiracle?

Answer 1

Insects breathe through the tracheae, a complicated network of tubules. Large tracheae connect to spiracles, which open at the body's surface and allow air and carbon dioxide to enter and depart. Spiracles are found on the body's pleural surface, usually one on each side of each segment.

Complete answer:
Air enters the respiratory systems of insects through a series of exterior apertures known as spiracles. These spiracles, which in certain insects serve as muscle valves, lead to the internal breathing system, which is made up of a densely networked array of tubes known as tracheae.

Consider the insect respiratory system as a sponge to understand it better. Small holes in the sponge allow water to enter and saturate it. Similarly, the spiracle apertures allow air to enter the insect's internal tracheal system, providing oxygen to its tissues. The spiracles are where carbon dioxide, a metabolic byproduct, leaves the body. ​

Humans have a combined respiratory and circulatory system, in which oxygen is delivered to muscles and tissues through the bloodstream in a closed system. Respiration is distinct from the circulatory system of insects. Tracheae are a network of tubes that exchange oxygen and carbon dioxide gases. Insects breathe by spiracles, which are apertures in the thorax and abdomen, rather than noses. Diapausing or non-mobile insects have a lower metabolic rate and use less oxygen.

Note:-
The respiratory system of insects is more efficient than that of humans. In relation to their physical size, they can take in more oxygen than we can. Most insects have the ability to open and close their spiracles, allowing for "constant gas exchange". Insects with closed spiracles recycle oxygen in the tracheae and can survive without breathing continuously.