Ventilation

To ventilate the respiratory system, opposing sets of abdominal muscles contract alternately like a bellows, producing dorsal-ventral and lengthwise contractions and expansion of the abdomen. To move air through the spiracles, the air sacs must also expand and contract from the alternate compressions and expansions of the abdomen. Because the air sacs are collapsible, hemolymph can shift in the hemocoel as the intestinal tract expands and contracts with feedings. Air sacs may allow growth of organs without changing the exterior form of an insect's body. The tracheae themselves are more or less rigid, as they possess spiral thickenings of cuticle within their walls that keep them open. Hence, the tubes themselves do not respond much to increases and decreases of pressure around them, but the thinner air sacs do.

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