Caterpillars are well adapted for feeding and growth. A newly hatched tomato hornworm caterpillar is less than 5 mm in length (1/4 inch). In a couple of weeks it can grow to thousands of times its initial weight.
The caterpillars form within tiny green eggs and chew their way out of the egg shell with their sharp mouthparts. A newly emerged caterpillar has a body that is soft and flexible. The flexibility is necessary for the caterpillar to maintain a compact form inside the egg. Once it has reached the outside world, the cuticle on the outside of the caterpillar can unfold into a shape that is larger than could be stuffed back into the egg.
A caterpillar that has just emerged from the egg is a white color. After the caterpillar unfolds, parts of the cuticle will harden and darken as the proteins that for the cuticle are cross-linked. The caterpillar goes from a creamy white to a light tan color. Entomologists refer to the hardening and cross-linking process as “tanning”.
Hornworms get their name from the distinctive black horn on the tip of the abdomen. The horn is flexible when the caterpillar is in the egg and may have a crumpled or droopy appearance when the caterpillar first emerges. The horn eventually will straighten as the caterpillar ages.
The tomato hornworms will grow up to eat a lot of tomato leaves. A gardener my find a healthy tomato plant missing quite a few leaves if hornworms are present. Like so many animals, the “baby” caterpillars are cute, but like all “cute” babies, they grow up into stages that are far less charming.