Caterpillars

Caterpillars are the larval forms of moths and butterflies.

You generally won’t see moth or butterfly eggs, unless you look closely. During plant dormancy, these eggs may be on the underside of leaves, tucked into the crevice of bark, or hidden under leaf litter or in the soil. As temperatures rise, caterpillars invade our garden en force. 

Hornworms (pictured below), cutworms, and budworms are all caterpillars. Caterpillars are often responsible for leaf damage, but some varieties feed on roots, buds, flowers, and tree trunks. There are even caterpillars that feed on your clothing, moths that feed exclusively on the hooves of dead ungulates, and caterpillars that eat other caterpillars! Caterpillars have only one purpose and that is to feed. Most caterpillar species molt their skin four or five times as they consume as much plant material as they can, before pupating. As much as we dislike the damage caused by adolescent caterpillars, adult moths and butterflies are good pollinators, so it’s a toss-up.

Tomato hornworms can destroy tomato plants in short order

Caterpillar control

Some plants, such as lima beans, emit chemicals that call out to parasitic wasps whenever caterpillars start feeding. In this way, they protect themselves. Spiders, soldier beetles, green lacewings, praying mantis, pirate bugs, ground beetles, assassin bugs, bats, birds, lizards, frogs and toads all enjoy feeding on caterpillars. You can make their job easier by avoiding the use of chemicals and by providing a clean water supply.

If your caterpillar problem gets bad, you can apply Bacillus thuringiensis (Bt). Bt is a naturally occurring, pest-killing bacteria found in soil, animal feces, and in the gut of the caterpillar stage of some moths and butterflies! There are different types of Bt that can kill different types of caterpillars. [Don’t be confused. There are bacteria in our digestive systems that can kill us, too.]

Some caterpillars can be thwarted from climbing host plants by applying sticky barriers around trunks and stems. Row covers can also be used to protect vulnerable plants, just be sure there are no eggs under the leaves or you will be protecting destructive caterpillars from their natural enemies! 

Horticultural oil works better at controlling caterpillar eggs, while neem oil can be effective against actual caterpillars. The best thing you can do is to be observant. Light or moderate feeding will not harm plants. Many of the larger caterpillars, such as hornworms, can simply be handpicked and tossed in the trash. I feed them to my chickens.

Not all bad

A few days ago, I noticed black flecks on my fennel leaves. Closer inspection showed nearly a dozen tiny black caterpillars with white saddles, and one particularly large specimen (below) that made identification easy. They were all the caterpillar stage of the black swallowtail butterfly. Well, I’m not a big fan of fennel, and the butterflies are lovely, so they can feed all they like and I will keep a look out for their chrysalis.

Black swallowtail caterpillar