There are dozens of different insects that are found on and/or around horticultural crops which may or may not attack the crops. Some are aggressive and voracious and others just nibble at the fringes. Some are just present.
Caterpillars are the immature form of butterflies and moths, which fall in the order Lepidoptera. Caterpillars feed on all plant parts and grow rapidly through several stages until they enter a pupation stage.
Caterpillars have soft, segmented bodies, which are divided into 3 parts or segments. Each segment possesses a number of specific anatomical characteristics, which allows identification and differentiation. The 3 segments include:
1) Head – well-defined, toughened or sclerotized head capsule
2) Thorax – three segments bearing 1 pair of true legs per segment
3) Abdomen – ten abdominal segments with 3 to 5 pairs of fleshy/stubby prolegs (1 pair is typically on the last [anal] segment)
Caterpillars differ in a number of features or characteristics, giving them their variation in appearance. Some caterpillars are smooth and hairless, while others have differing lengths and densities of hair or spines. Colouration can also vary, as well as whether they have any striping, spotting or other distinctive features. If you get really up close and personal with a caterpillar, you can also tell the difference between species using more detailed or hard to see features, such as how the hooks on their anal proleg are arranged or what their face is shaped like.
Source : Agriculture and Forestry