Friday Cat-erpillar Blogging

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.

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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4 Responses to Friday Cat-erpillar Blogging

  1. Alicia says:

    I am amazed at how fast these caterpillars can grow! As part of a class project I received a young tomato hornworm caterpillar and have been observing it for 3 days. Within just these 3 days I have already noticed a difference in size and color. The day I received my caterpillar it was a little more than a half inch long. Just a couple of days later it was nearly an inch long! The color was a very light green and now I can see just a little more green in it. At first I was not sure why this caterpillar was called a hornworm, but I can see the little black horn unfolding from the caterpillar. I am really anxious to see how my caterpillar progresses through its life cycle. I want to know about how long the life cycle takes to complete.

  2. Kali Stageman says:

    I’m really glad to find out how quickly hornworms grow because when we first saw them in class a few weeks ago, they were so tiny that you could barely see them. I got my caterpillar today and it is nearly an inch long and I can already see its horn. Also, I’ve been hearing that the caterpillars are typically green, but mine is bright blue. I wonder why mine’s blue…

  3. jjneal says:

    The green color comes from plant pigments. If the caterpillars are not eating fresh leaves, they will not be green.

  4. Xiayu Yuan says:

    I couldn’t imagine how fast a tomato hornworm caterpillar could grow until I got one as my pet from entomology class on Feb 3. It was only 1.5 cm in length and looked very fragile. I felt I could even look through its body. On Feb 5, only three days after, it became 1 cm longer and apparently much thicker. And its horn has blackened and straightened. I searched for some pictures of tomato hornworm caterpillar and I realized it will grow big and plump and the color will be nice. I can’t wait to see how my caterpillar will be like in next couple of weeks.

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