My Conversion to Caterpillars

Lobeza medina, moth at Finca Cantaros. ID by Isidro Chacon.

Lobeza medina, moth at Finca Cantaros. Identification of caterpillar by Isidro Chacon.

Caterpillars get such short shrift. Most people living in urban environments probably have never seen a caterpillar, but are familiar with the order Lepidoptera only because they’ve seen a few moths at the back door light, or seen a few butterflies in a local park. But in some U.S. cities they might spend $30 per person to visit a butterfly exhibit at the local natural history museum. The lovely colors and fragility of fluttering winged bodies draw people to them to an intense degree. Children and adults alike are entranced by butterflies and their association with flowers in full bloom.

Opsiphanes quiteria, butterfly larva at Finca Cantaros. ID by Isidro Chacon.

Opsiphanes quiteria, butterfly larva at Finca Cantaros. Identification of caterpillar by Isidro Chacon.

In the Northeastern United States, where I spent most of my childhood in country or exurban settings, caterpillars are not very charismatic—often dark, hairy and not eye-catching. Many moth and some butterfly larvae there are treated as pests, consuming leaves of garden plants or cherished native trees. However, at mid-life when I moved to Costa Rica, my attitude changed. The abundance of species of Lepidoptera meant many more opportunities to see not only the beautiful and diverse flying adults in gardens and forests (and under black lights in research settings), but also to see a stunning variety of strange and arresting caterpillars.

A memorable day in early 1989, soon after I arrived in Costa Rica, was the day I visited Dr. Dan Janzen and his wife Dr. Winnie Hallwachs, University of Pennsylvania professors of biology and legends in Costa Rica for their conservation work (along with hundreds of others) to establish the Guanacaste World Heritage Site and National Park. Dan and Winnie welcomed me, and my former husband Luis Diego Gómez, to their modest home in Santa Rosa. Before he shook my hand Dan presented me with a boa constrictor to hold and wrap around my arms. Soon after this rite of passage, we went inside for coffee, and they paid no attention to the ants crawling around the sugar bowl, mixing them into their coffee without a word. Of course, I did the same.

There was an odd smell of decay permeating the house. Hanging around the dining area on cords were dozens of little white air-permeable stained cloth bags, some filled with chrysalises (pupae) and others with caterpillars eating leaves. Winnie and Dan were rearing caterpillars, a process taking anywhere from ten to sixty days, and then protecting and checking daily the pupae to see what butterfly or moth would emerge. The unpleasant smell was from molts left over from the changing of the larval instars (the growth process which typically involves five molts), and probably from the decaying frass, the waste of the plant digestion process. This was a labor-intensive job, requiring removing the frass from the bags multiple times daily. Dan and Winnie’s research on Lepidoptera, and many other organisms, is simply prodigious. Later that day, for example, we went out to collect Baird’s Tapir dung so Dan could see what species of seeds it contained.

Parides erithalion, butterfly at Finca Cantaros. ID by Isidro Chacon.

Parides erithalion, butterfly at Finca Cantaros. Identification of caterpillar by Isidro Chacon.

From a while after that, I was hooked. I raised some larvae myself and took more interest in trying to determine what caterpillar would turn into which butterfly. It wasn’t easy. While in the bags with their host leaves, some fell victim to fungi or viruses. When butterflies actually emerged from their pupae, success was exciting. That was many years ago. Now, I just take photos when I am fortunate enough to spot a bizarre and ornately patterned caterpillar.

In light of disappearing biodiversity, study and dissemination of research about these creatures, often co-evolved with only one or a very small number of plant species, can literally help save tropical forests. People who want to save butterflies (and birds, and jaguars) must also work to save caterpillars and their host plants.

Below are my top ten favorite facts about caterpillars that even David Letterman would love:

Tiny caterpillar with stinging hairs.

Tiny caterpillar with long, barbed stinging hairs.


  1. Caterpillars’ heads have mandibles containing both molars and incisors which become worn down as the larva matures, but they are replaced at each molt, so each instar starts its life with a whole new set of sharp mandibles.
  2. Oh, and the head falls off, too. Each instar starts with a whole new noggin.
  3. While most butterfly caterpillars eat vegetable matter, some survive on the flesh or the secretions of other insects.
  4. If one individual caterpillar delays molting a day or two after the rest of the group, it is at risk of being cannibalized by the others.
  5. Caterpillars have eyes called stemmata, which contain light-sensitive pigments that not only distinguish between light and dark, but between horizontal and vertical. Some research shows stemmata produce a well-focused image.
  6. Caterpillars produce safety lines of silk connected to the plant as they walk along—otherwise an early instar caterpillar that falls off its leaf will likely starve, as it is too small to find its way from the ground and up the plant to tender leaves.
  7. All butterfly caterpillars have bristle-like hairs called setae at some stage in their development—lengths and density vary tremendously—that are mostly used for physical defense, but sometimes also for chemical defense, against ants, insects and other predators.
  8. Voracious eaters, most caterpillars can increase their weight up to 60 times in less than two weeks. Some moth species may increase weight from egg to mature instar by 200 times or more.
  9. Early, small instars eat constantly, day and night, but later instar, larger caterpillars have evolved to stay immobile and quiet by day, eating only at night to avoid being seen by predators.
  10. The caterpillars of some butterfly species hang out in gangs—see the “gregarious” larvae below—to protect against predators. Large groups can work together to cut through tough leaves. Solitary types are more cryptic in color so they can hide out; gregarious types are usually more obvious in color—often aposematically so. (Their bright colors warn predators off—“don’t eat me, I’m toxic.”)

    Eumeus godartii, butterfly at Las Cruces Biological Station. Gregarious, aposematic, with toxins from the plant it eats, Zamia fairchildiana

    Eumeus godartii, butterfly larvae at Las Cruces Biological Station. Gregarious, aposematic, with toxins from the plant it eats, the Cycad Zamia fairchildiana. Larvae have an unpleasant odor. Note setae (hairs) that look nasty, but do not sting.

My reference guides for the top ten list: The Butterflies of Costa Rica and Their Natural History, Volumes I (1987) pp. 5-8; and II (1997) pp. 9-18, by Philip J. DeVries, Princeton University Press.





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