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The Parts of a Caterpillar

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Caterpillar Diagram
The Parts of a Caterpillar
Image: A. M. Liosi/Wikimedia Commons (CC license), modified by Debbie Hadley, WILD Jersey

Caterpillars come in many colors, shapes, and sizes. Some caterpillars are quite hairy, while others are smooth. Regardless of these varied features, all caterpillars share certain morphological features. These common features are labeled and described in this caterpillar diagram.

  1. head - the first section of the caterpillar body. The head includes the eyes, called stemmata, the mouthparts, the small antennae, and the spinnerets, from which the caterpillar produces silk.

  2. thorax - the second section of the caterpillar body. The thorax consists of 3 segments (T1, T2, and T3), 3 pairs of true legs, and a dorsal plate called the prothoracic shield.

  3. abdomen - the third section of the caterpillar body. The abdomen is 10 segments long (A1-A10), and includes the prolegs, most of the spiracles, and the anus.

  4. segment - a section of the thorax or abdomen. A caterpillar has 3 thoracic segments and 10 abdominal segments.

  5. horn - a dorsal projection present on some caterpillars, such as hornworms. The horn may help camouflage the larva.

  6. prolegs - unsegmented legs, usually found in pairs on the 3rd through 6th abdominal segments. The soft prolegs bear hooks on the ends which the caterpillar uses to cling on to surfaces. The number and size of the prolegs can be an identifying characteristic.

  7. spiracle - an external opening of the tracheal system that allows gas exchange (respiration). The caterpillar contracts muscles to open and close the spiracles. One spiracle pair is on the first thoracic segment (T1); the other 8 pairs are on the first 8 abdominal segments (A1-A8).

  8. true legs - three pairs of segmented legs, also known as thoracic legs, located in pairs on each of the three thoracic segments. Each true leg ends in a tiny claw.

  9. mandibles - the jaws, used for chewing.

  10. anal prolegs - a pair of unsegmented legs located on the last abdominal segment.


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