The Caterpillar Effect
Last week my wife and I were in St. Martin and went to a butterfly farm where I learned something new. Something I feel like I should have already known. I have long been aware that butterflies have been declining in numbers due to loss of habitat and the use of pesticides. Over the years, both in my own yard as well as at some property I own west of Carrboro, I have been attempting to be helpful to butterflies by planting zinnias, butterfly bushes and other flowering plants. While at the butterfly farm I learned that I had been ignoring the needs of caterpillars, and that looking after the caterpillars was the part that really mattered. Reviewing the amazing life cycle of the butterfly makes this point quite clear.
Before we proceed, let’s review some of the key butterfly facts and figures.
- Butterflies have been around for 40 to 50 million years.
- Butterflies live on every continent except for Antarctica. Approximately 700 species of butterflies live in the United States.
- Although less efficient than the honey bee, butterflies play a very important role as pollinators for human food crops.
- They are also quite beautiful. The photo at the top of the page is a Buckeye butterfly taken at my Orange County property.
Let’s begin our review of the life cycle of the butterfly, starting with an adult female. Not long after spreading her wings for her first flight she will identify a mating partner. For some species of butterflies this involves an intricate mating ritual in which several males will compete for her attention. In other circumstances the males’ behavior is far less chivalrous and the viewpoint of the female is not taken into consideration. Once the mating pair as been determined, the interlude continues for approximately 48 hours. (Early drafts of this column included a number of jokes at this point that I thought to be rather clever, all of which, after a more prudent review, I decided to omit.)
Depending on the species, a female butterfly lives from 1 week to 9 months. During this time she will feed on nectar from flowers and lay her eggs, but in a very particular way. As I learned during my trip to the butterfly farm, once the eggs hatch into caterpillars, many species can only eat the leaves of a single plant. Therefore, the butterfly must lay her eggs on that particular plant for the caterpillars to survive and produce the next generation.
The moment I learned this, the inadequacy of my butterfly gardening efforts over the last several decades became clear. Sure, I had provided good sources of nectar for the butterflies to eat, but hadn’t given them a place to lay their eggs. This turns out to be a fairly major flaw. The decline of the butterfly population is driven much more strongly by the dearth of caterpillar host plants than a lack of flowers for the adults to feed from.
Caterpillars live for about two to three weeks, during which they eat and grow very, very rapidly. Once a caterpillar reaches a sufficient size, it selects the underside of a branch and weaves a small silk pad. The caterpillar is equipped with a small hook-like appendage called a cremaster which allows it to hang upside down from the silk pad. Then it sheds its skin to reveal a chrysalis, the hard shell which protects the growing butterfly, which it has already made from its own body.
One to two weeks later a butterfly will emerge, but not before one of the most amazing biologic processes on earth occurs. Inside the chrysalis, the body of the caterpillar complete breaks down to form a liquid consisting of undifferentiated cells called imaginal cells. These are akin to stem cells in humans and can be converted into any type of cell for the developing butterfly. As I sit back and consider the complexity of this transformation, I am awestruck. For me, it provides some additional insight into the power and pace of evolution. Butterflies have been perfecting their genetics and life cycle for 50 million years, ten times longer than the 5 million years that hominids have walked the earth. Consider what changes in human biology could occur in the next 45 million years if we manage to hold on that long.
In the meantime, I have been engaged in a total overhaul of my butterfly gardens to include caterpillar host plants. You can get more information on North Carolina butterflies and caterpillars on www.naba.org. In the meantime, next time you are planting please consider.
- tulip trees
The caterpillars, and butterflies, will be happy.
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