With Old Man winter still hanging around much of the nation, this week we again head to warmer places to visit insects in the Costa Rican cloud forest. Tropical cloud forests are among the most unique and biologically diverse biomes on planet earth. An unending source of wonder and beauty are tropical rainforests and cloud forests, which house plants and animals with secrets yet untold. From the bark of the willow tree, the source of aspirin, to the rosy periwinkle plant, the source of cancer-fighting vinblastine, almost half of our pharmaceutical agents are derived from natural sources, many of which are plants. Throughout the world these irreplaceable habitats are imperiled by human forces such as development, to which some 30 million acres of rainforest are lost annually.
Tropical cloud forests face another threat – global warming. Cloud forests form when moisture laden air rises from warm lowlands, cools and then condenses to form clouds that linger and cling to mountainsides. Cloud forests are the crucible for the evolution of thousands of species of organisms found nowhere else on the planet. But cloud forests and their denizens have a problem. As global temperatures warm, moist air, the wellspring of cloud forests, must ascend to ever higher elevations to condense and form a cloud. Unfortunately, mountains are not infinitely high and eventually cloud forests and their biotas disappear. This process is already underway in places like Costa Rica where species endemic to warming dryer lowlands are now invading cloud forests to the detriment of indigenous animals. In talking about the threat of climate change to cloud forests and their residents, famed tropical ecologist Dan Janzen says, “The bad thing about living on top of the mountain is that there’s nowhere to go.”
On a typical rainy day in the cloud forest, insects go about their business in the usual ways. Beneath the frond on a fern a spectacular saturniid moth hides during the daylight hours awaiting nightfall when he will seek a mate. This gorgeous tropical species is a relative of large saturniid moths such as the Io moth and Royal Walnut moth we visited in previous episodes. Notice the feathery antennae, the hallmark of males of many species of moths. Not much farther along the mountain trail, a delicate Ithomiine butterfly balances a drop of liquid in the coils of its proboscis. Adults of these clear-winged butterflies obtain noxious chemicals called pyrrolizidine alkaloids from flowers of tropical members of the aster and forget-me-not families. These compounds are known to deter vertebrate predators including birds as well as invertebrates such as spiders.
Notice the feathery antennae of this gorgeous male saturniid moth as it rests beneath a fern frond.
Ithomiine butterflies are difficult to spot as they move through vegetation in the dark forest. Will the butterfly sip the droplet of fluid captured in its proboscis?
On the stem of a nearby plant a beautiful froghopper sucks plant sap in the rain. For it to obtain sufficient nutrients for growth and development, large volumes of sap must be removed from a plant. The excess is squirted out the rear end as an excretion known as honeydew. On a rainy day in the cloud forest it is impossible to know how much of the rain falls from the sky and how much of the rain comes from the alimentary tract of sap-sucking insects. We met other kin of the froghopper clan in previous episodes. Not everyone will have the good fortune to visit the cloud forest and the irreplaceable creatures residing therein, but we all have a role to play in preserving these unique, diverse places.
Bug of the Week thanks bold Dr. Shrewsbury for risking elimination from the mountaintop by fierce winds and providing inspiration for this episode. We thank Dr. Don Harvey of the Smithsonian Institution for identifying Cerodirphia avenata, the drop dead gorgeous silk moth featured in this story. The wonderful references “Mother Nature's Medicine Cabinet” by Kate Wong, “Withering clouds: Climate change damaging biodiverse Costa Rica forest” by Ryan Schuessler, and “Adult-obtained pyrrolizidine alkaloids defend ithomiine butterflies against a spider predator” by Keith S. Brown Jr. were consulted to prepare this episode.
Two bug geeks learn that atop the mountain in a cloud forest it is both windy and, yes, cloudy.