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01 - Head - The first section of the body is the head. It includes six eyes (stemmata), the mouthparts, the small antennae, and the spinnerets, from which the caterpillar produces silk. Antennae are present on either side of the labrum but are small and inconspicuous. The labrum is like an upper lip. It is used to hold food in place while the mandibles chew.
02 - Thorax - The thorax is the second section of the body. It consists of three segments. The thorax contains three pairs of true legs with hooks and a dorsal plate called the prothoracic shield. The prothoracic shield is located on the first segment. The color pattern of this shield is valuable for identifying different species of caterpillars.
03 - Abdomen - The third section of the caterpillar body. It is 10 segments long, and includes the false legs (prolegs), most of the breathing holes used for respiration (spiracles) , and the the final stop along the digestive tract (anus).
04 - Segment - A body section of the thorax or abdomen. A caterpillar has three thoracic segments and 10 abdominal segments.
05 - Horn - A dorsal projection present on some caterpillars such as hornworms. The horn may help camouflage the larva. It may also be used to frighten away predators.
06 - Prolegs - Are fleshy, false, unsegmented legs, found in pairs on the third through sixth abdominal segments. The soft prolegs bear hooks on the ends which the caterpillar uses to cling to foliage, bark, and silk. Experts sometimes use the arrangement and the length of these hooks to identify caterpillars at the family level. The number and size of the prolegs can also be considered identifying characteristics.
07 - Spiracles - Are external openings that allow gas exchange (respiration). The caterpillar contracts muscles to open and close the spiracles. One spiracle pair is found on the first thoracic segment, and the other eight pairs are found on the first eight abdominal segments.
08 - True Legs - Are three pairs of segmented legs, also known as thoracic legs or true legs, located in pairs on each of the three thoracic segments. Each true leg ends in a tiny claw. These are distinct from the fleshy, false prolegs found along the abdominal cavity.
09 - Mandibles - Located in the head section, mandibles are jaws that are used for chewing leaves.
10 - Anal Prolegs - are a pair of unsegmented, false legs that are located on the last abdominal segment. The prolegs on A-10 are usually well developed.
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