[ 2008-01-16 17:29 ]
Insects breathe in a way that is very different from us. Instead of having a central place to gather oxygen and a transport system to deliver the oxygen to all of the cells of the body like us, insects have a system of fine branching tubes called a tracheal system that delivers the oxygen directly to each cell in the body.
When breathed in an insect, an oxygen molecule in the atmosphere enters a tiny hole on the insect's thorax or abdomen called aspiracle. The spiracle is the opening of a long tube called tracheae. Then the oxygen molecule proceeds down the tracheae, which is a long, air-filled, branching tube. It continues to move through branches until reach a tiny, fluid-filled, dead end calledtracheole, and dissolve in the fluid. From the fluid, it diffuses or moves across the wall of the tracheole into an insect cell such as a muscle cell.
The movement of air through thetracheal systemof most insects relies solely ondiffusion. Because most insects rely on diffusion, which occurs best over small distances, they cannot get very large. You will not see huge ants, like in the movie "Them," because enough air could not diffuse that far into their bodies to keep their cells alive. However, some larger insects can use theirabdominalmuscles to force air in and out of the tracheal system in a limited way.
So, with this system in mind, it would be difficult tostranglea bug. However, if the tracheal system fills with water, it takes much longer for air to diffuse through the system. Therefore, an insect can drown fairly easily.
tracheal system: 气管系统
（来源：coolquiz.com 英语点津 Annabel 编辑）