What Is a Caterpillar—Really?

Gulf fritillary caterpillar

Gulf Fritillary butterfly larvae. Photo courtesy S. Lee

You don’t have to be a gardener to experience caterpillars. In fact, from Absolem, the pipe-smoking caterpillar Alice found in Wonderland to more real world curious characters, we’ve grown up with these critters.

Officially a caterpillar is the larva of a butterfly or moth, consisting of a segmented, wormlike body with 3 pairs of true legs and other appendages that are not. Caterpillar bodies can be smooth, hairy, brightly colored to warn potential predators away, or so well camouflaged we literally don’t see them in front of our noses. If you grow tomatoes and have encountered tomato hornworms, you understand exactly.

However, we delight in the appearance of some caterpillars since they are a stage in the life cycle of a favorite winged insect, the butterfly.

The point is there are caterpillars we welcome to our flowerbeds and gardens and those we don’t. The other point is what kills the ones we don’t want i.e. the THW (tomato horn worm) also kills the larvae (caterpillars) of Monarch butterflies.

In gardens, both the ornamental and edible ones, this conflict is easy to observe.

Growing Maypop or Passion flower vine produces a tangle of light to dark purple flowers that add delight to our gardens while leaves of the vine are a feast for larva of Gulf Fritillary butterfly.

On the other hand, tomato plants in your backyard garden are prey to the tomato horn worm, which feeds just as voraciously as Gulf Fritillary butterfly larvae but isn’t nearly as welcome. But they’re both caterpillars. Which means if we’re controlling the pest, we’re likely harming the welcome visitor.

What’s a gardener or nature lover to do with these leaf-chomping critters that become aerial flowers as adults?

Gulf fritillary butterfly

Gulf Fritillary butterfly on Maypop flower

Keep in mind the bees, butterflies, and other beneficial insects that happen to pollinate our gardens, crops, and flower beds are primarily attracted to flowers because that’s where the nectar and pollen are produced. Therefore, any material used to treat caterpillars should be applied responsibly when flowers (blooms) have fallen off, are not open, or were not attractive in the first place.

Using the tomato horn worm feasting on tomato plant leaves and fruit as example, tomato blooms don’t have to be insect pollinated to product tomatoes although some research indicates insect pollination may improve production. But the dang tomato horn worms can undo all our effort in a few short days. Control options start with the most bee and butterfly friendly options – hand pick the caterpillar (worms). Drop them into soapy water, they drown. Put them under a shoe, they squish. Throw them out where birds can get to them, they’re supper.

Ramping up management options are microbial insecticides that are lower in toxicity to animals and humans, making them a less questionable option. Most of these products are also more specific than general population materials, a positive attribute if we’re targeting pests and trying to spare beneficials. Bacillus thuringiensis is one of the more widely known and used of this category has limitations, such as being most effective on young larval stages, not adults. Another insect toxin with broader powers is spinosad that when applied at label rates is less risky to birds, fish, and some beneficial insects. It is however, toxic to bees and therefore should not be applied to plants in flower. Realistically knowing we sometimes have no choice, spraying late in the day reduces the harmful impact to pollinating insects.

So what is a caterpillar? A stage in the life cycle of butterflies and other insects that delights or frustrates us. Be aware of impacts our actions have on both categories.

By Sallie Lee, Urban Regional Extension Agent, Alabama Cooperative Extension System.  Contact Sallie at leesall@aces.edu.


The Alabama Cooperative Extension System (ACES) operates as the primary outreach organization for the land-grant functions of Alabama A&M and Auburn Universities. ACES is committed to affirmative action, equal opportunity and the diversity of its workforce.  Educational programs of ACES serve all people regardless of race, color, age, sex, religion, disability, sexual orientation, or national origin.

Alabama Extension

The Alabama Cooperative Extension System operates as the primary outreach organization for the land-grant functions of Alabama A&M and Auburn Universities and answers home-gardeners' questions each week on Birmingham Gardening Today.

Leave a Reply

Your email address will not be published. Required fields are marked *