Friday Cat-erpillar Blogging: Air Supply

Insects get their supply of oxygen from trachea, tubes that open to the outside at the spiracles (muscular valves) and branch to deliver oxygen to every cell in the body. Trachea must be large enough to accommodate the oxygen requirements of the insect. Trachea must be small enough to allow space for water and other tissues inside the insect. In a small caterpillar, the distance from the outside to the cells that require oxygen is minimal. As the caterpillar grows, the distance from the outside to the internal cells increases and the numbers of cells increase. Our caterpillar “outgrows” its tracheal system and the amount of oxygen that can be supplied becomes limiting.

Spiracle of a hornworm caterpillar.  At the molt, the cuticle of the spiracles along with the cuticle lining the insides of the trachea are shed.

Spiracle of a hornworm caterpillar. At the molt, the cuticle of the spiracles along with the cuticle lining the insides of the trachea are shed.

The trachea must be expanded at the molt. The trachea of insects are lined with cuticle that is shed at each molt. During the molt, the old cuticle of a trachea separates from the tracheal cells and the new larger tracheal lining (cuticle) is secreted into the newly created space between cells and the old cuticle. The tracheal cells can increase in size and number to create a substantially larger trachea. When the insect molts from its old cuticle, the old lining of the trachea, still attached to the spiracles, is pulled from the center of the new trachea.

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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