For every action in nature there is an equal and opposite reaction if you were to subscribe to Newton’s third law.
As you must already suspect, Newton wasn’t thinking about native plants, moths, butterflies, their caterpillar larvae stage nor bugs. However, it’s really just all about the food chain, isn’t it? Circle of life and all that; hunter/huntress/victim.
The victims in my story are the caterpillars. My first love was butterflies, then dragonflies, then plants, and fascination grew to caterpillars, moths and bugs. But it really all revolves around plants, specifically geographically native plants.
Famed and much quoted entomologist/educator/author Doug Tallamy, at the University of Delaware, has told the world via his popular books and lectures that caterpillars are the prime food for bringing up nestlings. I like birds, too – but my equilibrium was drastically jarred to hear caterpillars are just so much food fodder.
As Texas Master Naturalists, we promote using native plants. And that’s a good thing. Tallamy’s research certainly supports that concept, saying “it is crucial to recognize the role native plants play in supporting caterpillar populations and as a result, attract and support a more diverse range of bird species, creating thriving ecosystems.” The conclusion of that statement is that caterpillars are a primary food source for baby birds.
Articles on popular birding websites have picked up the theme. In a “Nest Watch” article at the Cornell Lab of Ornithology website, Debra Breton, in an article entitled “Caterpillar: It’s What’s for Dinner,” wrote: “A single pair of breeding chickadees must find 6,000 to 9,000 caterpillars to rear one clutch of young, according to Doug Tallamy, a professor of entomology and wildlife ecology at the University of Delaware.” That’s a lot of caterpillars; it’s a wonder we have butterflies or moths at all. My thoughts calculate such: less caterpillars, less butterflies and moths. That’s sad.
While we have no chickadees of any species in the Rio Grande Valley, Carolina chickadees are permanent residents in parts of Texas and breed as far south as Houston. Tallamy also professes that 96 percent of terrestrial birds rear their young on insects – and caterpillars are a particularly important food source. Author Jeff Tome, in an Audubon Community Nature Center web article entitled, “The early bird gets the caterpillar,” reported, “In one notable study, researcher Doug Tallamy, found that one chickadee family fed their babies 350 to 570 caterpillars every day.”
Caterpillars are extremely high in fat and protein, deriving those nutrients from host (native) plants. Rio Grande Valley resident birds, like black-crested titmice, roadrunners and groove-billed ani eat caterpillars; green jays, northern cardinals and grackles feed their young caterpillars. The list goes on.
Yes, birds are exciting, I certainly wouldn’t want a world without them. And it’s not their fault they were created to make a hefty dent in the butterfly and moth populations. But if their aerial strafing isn’t tragic enough, here’s another startling piece of information: Caterpillars are vulnerable to attack from ground warfare, too. I found out that shocker one dark, pre-dawn morning.
I was identifying insects that had been attracted to the black light at my moth sheet. I uploaded an observation to iNaturalis.org via my phone app of a particularly striking looking bug that photographed in good detail. It was identified as a black caterpillar hunter, colosoma sayi.
What? A caterpillar hunter? That’s a pretty specific occupation, a bug that targets caterpillars. Whyever for, I wondered? However deadly the hunter may be, I was not the first to recognize the bug as being good looking. C. sayi is a species in the Ground Beetles family and genus Calosoma. Calosoma is Greek for kalos, beautiful and soma for body. But I digress.
Later, when I was at my computer, I looked through my photos and found I had similar looking beetles that were identified only by their scientific name and a short annotation: “species of ground beetle.”
One such bug was a pretty, green metallic beetle: Calosoma aurocinctum. Another black beetle identified as Calosoma marginale, also annotated as ground beetle.
I opened the iNaturalist.org website and did a search for caterpillar hunter beetles. C. aurocinctum and C. marginale were included with the C. savi in my observations. So, now I realized not only does my yard have a number of birds feasting on potential butterflies and moths during the day, a beetle brigade, like stealth bounty hunters, is reducing the number of caterpillars under cover of darkness. But it gets worse.
During one early October morning foray into the pre-dawn dark last year, a black caterpillar hunter was on the moth sheet. It was the C. marginale. I didn’t give it another thought because caterpillars aren’t attracted to moth sheets. Had I read more about these beetles, I would have been more attuned to the safety of the moths that were on the sheet.
I was checking the back side of the moth sheet, and when I came round again to the front, I was aghast to find that caterpillar hunter devouring the body of a pretty Heiligbrodt’s mesquite moth, Syssphinx heiligbrodti, – of which I’d uploaded a photo to iNaturalist.org just moments prior. It was too late to attempt rescue. Sadly, quickly, the wings had fallen to the pavement, leaving a ghost of the pretty moth’s body, and no sign of the killer.
The tribe of Calosoma beetles are all great hunters; the genus occurs around the world. For all the horrors in my tale, the beetles are considered to be the good guys and are beneficial in a garden. The species C. sayi, named for Thomas Say, an American entomologist (1787-1834), is especially fond of caterpillars, its favorite is the caterpillar of the dreaded gypsy moth as well as army worms.
Caterpillar hunter beetles are found primarily throughout the Northern Hemisphere, with some 167 species. They are about 0.9 to 1.1 inches in length. Their grooved elytra (the tough forewings of beetles used to protect the more delicate hind wings) have rows of metallic dots or pits. They are nocturnal beetles, often drawn to lights. As I discovered, they are an equal opportunity predator, eating other insects and larvae, not just caterpillars.
Caterpillar hunter beetles’ eggs are laid singly in soil. The larvae live in soil and overwinter and emerge in late spring or early summer as adults. Adults overwinter under fallen logs and leaf debris. Adults can live two to three years. The adult beetles can give a nasty bite and also are equipped with scent bladders or glands that can defensively release a fluid with a strong musky odor.
Several species of this beetle are notably black. Some are colorful metallic like the C. aurocinctum. Another important local species in this genus, as yet to be discovered at my black light set up, is a deeply grooved metallic green with near-neon reddish-orange edging, the fiery searcher caterpillar hunter, Calosoma scrutator, which also would be found feeding on gypsy moths.
Destructive webworms and tent caterpillars’ natural enemies are flies, wasps, birds and predaceous beetles, like the caterpillar hunter beetles. To assist these predators, break open the webs when you come across them.
It’s sometimes hard to remember when there is a natural balance, everything thrives. Butterflies will continue their species, visiting my native flowering plants by day as will interesting moths and insects to my moth sheet by night.
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These websites were helpful in writing this article: Davesgarden.com, Texassento.net, bugGuide.net.