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A spiracle or stigma is the opening in the exoskeletons of insects, myriapods, velvet worms and many arachnids to allow air to enter the trachea. [ 1 ] [ 2 ] [ 3 ] In the respiratory system of insects , the tracheal tubes primarily deliver oxygen directly into the animals' tissues .
Insects have spiracles on their exoskeletons to allow air to enter the trachea. [1] [page needed] In insects, the tracheal tubes primarily deliver oxygen directly into the insects' tissues. The spiracles can be opened and closed in an efficient manner to reduce water loss. This is done by contracting closer muscles surrounding the spiracle.
Stylized diagram of insect digestive tract showing malpighian tubule, from an insect of the order Orthoptera. The first section of the alimentary canal is the foregut (element 27 in numbered diagram), or stomodaeum. The foregut is lined with a cuticular lining made of chitin and proteins as protection from tough food.
During the closed phase of discontinuous gas exchange cycles, the spiracle muscles contract, causing the spiracles to shut tight. At the initiation of the closed phase, the partial pressure of both O 2 and CO 2 is close to that of the external environment, but closure of the spiracles drastically reduces the capacity for the exchange of gases with the external environment. [2]
Respiration is performed using tracheae, air-filled tubes, which open at the surfaces of the thorax and abdomen through pairs of valved spiracles. Larger insects may need to actively ventilate their bodies by opening some spiracles while others remain closed, using abdominal muscles to expand and contract the body and pump air through the system.
The forelegs are reduced in the Nymphalidae Diagram of an insect leg. The thorax, which develops from segments 2, 3, and 4 of the larva, consists of three invisibly divided segments, namely prothorax, metathorax, and mesothorax. [11] The organs of insect locomotion – the legs and wings – are borne on the thorax.
The posterior spiracles (on the anal segment) are usually on two cylindrical lobes. Each spiracle has three slit or oval openings and three or five groups of interspiracular hairs that are branched in some species. [citation needed] The larvae are microbial grazers found in abundance in many microenvironments with decomposing organic material.
These lead to spiracles into which the air is taken. Once the larvae grow to some size, they move to soil at the edge of water and burrow into a cell and pupate. The adults breathe by going to the surface and upending. They collect air under their elytra and are able to breathe this collected air using spiracles hidden under the elytra.