A World Within Worlds: How Berries Grow Caterpillars and Wasps
During our visits with each other, we have spoken about how the past feeds the present and the present foreshadows the future. Mother Nature is both a caring nurturer and a stark reminder of the struggles of life. She is also a fortune teller and can give you hints as to what was once here before us, as well as what is just over the horizon of time. Just as we spoke about a new generation of the forest beginning when a nurse tree died and a woodpecker began drilling holes in the decaying wood, we will once again look at a serendipitous moment of nature rippling out across time and opening opportunities for species not yet on the landscape.
A couple of generations ago, right around this time of year, a bird ate the delicious and eye-catching purple berries of a native shrub. What bird ate that berry, we will never know. It might have been an American Robin. It may very well have been a Wood Thrush. For all we know, it could have been an Eastern Towhee, a Northern Mockingbird or even a Northern Cardinal. The exact species isn’t important. What is important was that one of our winged wonders consumed the lavender-colored fruit of the American Beautyberry (Callicarpa americana) and then chose to fly to Harmony Hill. And when they were flitting around the forests of this gorgeous ground, they defecated the seeds hidden inside the berries. Upon falling to the soil below, one or more of these seeds germinated and began what would become a healthy population of American Beautyberry on Harmony Hill. That moment brings us to today’s lesson on insects, caterpillars eating leaves, moths pollinating flowers at night and how wasps use the scent of injured leaves to find a host for their eggs and larvae.
There are several places on Harmony Hill where American Beautyberry can be found growing in dense hedgerows, providing shelter, habitat and food to a variety of species. These ecotones not only sit between the forests and open areas at Harmony Hill, but they also represent their own worlds within worlds. By simply looking a little more closely, we can see the same give-and-take of nature that one would normally expecting on a grand scale; just in the micro ecosystem created by this native plant.
When summer begins to yield to fall, the clock of nature seems to tick a little more rapidly and loudly. Many species of plants seem to be in a hurry to get their seeds ready to cast out into the world and many species of animals appear to have a bit more urgency to preparing for the colder and shorter days ahead. It is in that backdrop that we found today’s Nature Note playing out. The stem of an American Beautyberry looked awkwardly bare, sticking out from stems covered in leaves. When we stopped to see what might have caused the stem to be stripped of its greenery, we observed a caterpillar we thought might very well be grazing away. The Rustic Sphinx Moth (Manduca rustica) caterpillar was eating nonstop as we peered into the shrubbery.
A member of Sphingidae family of moths, Rustic Sphinx Moth caterpillars are often lumped into the group of caterpillars called “hornworms” by many. Indeed, the “tail” of the caterpillar resembles a horn emerging from the rear of animal. That protuberance is an easily identifiable field marking shared by other familiar caterpillars, such as the Tomato Hornworm (Manduca quinquemaculata) and the Tobacco Hornworm (Manduca sexta). However, the tail of the Rustic Sphinx Moth caterpillar shows us how we can differentiate this species from his common cousins. Indeed, the caterpillars all look quite similar. While the “tails” of the Tomato Hornworm and the Tobacco Hornworm are smooth, the tail of the Rustic Sphinx Moth caterpillar is rough-looking (or granulated). Furthermore, American Beautyberry is a major larval food source of this caterpillar, making identification easy!
When it completes all its development, through several instars, the caterpillar will either climb down to the soil level or simply fall to the ground. Once there, it will burrow its 7”-9” body into the soil. When it settles into its subterranean setting, it will form a pupation chamber loosely around itself. There, it will go through metamorphosis and become an adult moth. The process will start over, as the adult female moths will lay their eggs on host plants for the caterpillars to start eating once they hatch.
Like so many of the Sphingidae moths, the Rustic Sphinx caterpillar will become a cryptically colored moth that takes to the skies in the evenings and feeds on nectar throughout the night. A mixture of grays, blacks, whites and browns cause this moth to blend into the barks of trees and the ground while at rest. However, when it takes to the wing, it looks eerily like a hummingbird. This leads to the common name of “hummingbird moth” this species shares with other members of Sphingidae. The only pop of color found on the adult is a series of orange dots on either side of the abdomen of the moth. Other than that, it relies and uses its camouflage to hide for potential predators.
There are a variety of plants that use Sphingidae moths to pollinate them, all of which have evolved long channels in their flowers that keep nectar away from all but the longest proboscises found on Hawkmoths. Members of the lily and evening primrose families are pollinated by Rustic Sphinx Moths, as well as the moths of other hornworms. These plants that attract Hawkmoths are called “sphingophilous” plants.
When we found the caterpillar in this installment, a rather obvious species was at work and became part of the story. As you can clearly see in the photos, there is something odd happening. What are those white, fuzzy things all over this hornworm? Remember when we told you there is a world within a world right inside the American Beautyberry? Well, here we see it! Let’s look a little closer and see what is going on!
There is a tiny parasatoid wasp patrolling the forests and fields of Harmony Hill. And this wasp is always sampling the air for scent molecules to find a host for its eggs and larvae. But, it isn’t keying in on the smells associated specifically with a host. Not at all. Instead, Cotesia congregata is on the hunt for chemical signals from injured leaves of American Beautyberry plants. Why would it do that? Well, where there are large areas with chemical cues of injured American Beautyberry leaves, there is a good chance this wasp will find the soft and large body of a hornworm just munching away at the leaves. And it is that caterpillar body in which it will lay its eggs!
Wait! It gets better!
When the female wasp finds a suitable host, like the hornworm in the photos, it begins inserting its ovipositor into the caterpillar to lay between 50-75 eggs. Along with the eggs, the female wasp injects a type of bracovirus inside, along with its venom. This polydnavirus works in conjunction with the venom to halt responses from the caterpillar’s immune system, effectively preventing the host’s body from attacking or working to ward off the wasp’s eggs. It also prevents any type of clotting of the hemplymp, or what many would consider the “blood-like” fluid in the caterpillar. That allows the developing larvae to consume the hemolymph. All these factors also inhibit any further development of the host, causing it to eat and live on; but, not allowing it to develop into an adult.
The wasp larvae develop just under the skin of the hornworm, feeding on the hemolymph unit it is time to emerge and pupate. This usually takes about 7-10 days.
They will burrow out of the hornworm and plant their tiny, white cocoons atop the caterpillar. They stay in their cocoons for about a week, before emerging as adult wasps.
And to think, this amazing story all began decades ago when an unsuspecting bird ate a berry and then flew to Harmony Hill! When we look at where the wasp pupa came from, we must look at the Rustic Sphinx Moth laying its eggs on an American Beautyberry. When we look at where the moth and caterpillar came from, we must look at the hedgerows of beautyberries on the land. And, when we look at where they came from, we are back to our unknown bird perching on a branch and defecating seeds onto the soils of Harmony Hill! Mother Nature is fortune teller and can show you the past, present and future… if you’re willing to stop, look, listen and heed her clues.