Costa Rican Caterpillars 2017-2018

Tom Davis

Last update: January 9, 2018
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This was the third time I helped with the Earthwatch project called Climate Change and Caterpillars in Costa Rica.

I wrote a much more extensive trip report when I did it in 1998, and wrote nothing about the 2014 trip. Even though that trip occurred almost 20 years previously, most of the things we did were similar: finding caterpillars, raising them to adulthood, and seeing what the adult looked like, or, if the caterpillar had been attacked by a parasitoid, seeing what emerged instead of a moth or butterfly. The parasitoids were usually either wasps or flies, but other things are possible.

I have done a lot of Earthwatch projects over the years, and many times I wrote up a trip report, and all of those are available one click away from my home page, here.

The Caterpillar Project

Goal of the project

See the links in the introduction above for detailed descriptions of the project, but the basic idea of the research was this: We wanted to collect as many caterpillars of as many different kinds as we could and collect enough of the host plant they were eating to provide food sufficient for them to mature as caterpillars, to form pupas, and to emerge as adults. All the caterpillars are members of the order Lepidoptera, meaning the butterflies and moths.

If a caterpillar is unlucky, it can be attacked by a parasitoid (usually a wasp or a fly) that lays eggs on, or injects eggs into the caterpillar's body, and as the caterpillar matures, so do the larvae of the wasp or fly. The parasitoids gradually eat most of the flesh of the caterpillar, and what emerges from the pupa is not a butterfly or moth, but rather wasps or flys.

Parasitoids are an important controlling force of caterpillar populations, so without them there would be more caterpillars and hence more plant destruction. Hence the study of parasitoids is important.

Where Were We?

All of us volunteers flew to San José, the capital city of Costa Rica and met for an introductory dinner the night before we took a bus to the research station.

All the research took place at the Organization for Tropical Studies (OTS) La Selva biological station. It consists of about 1600 hectares of lowland tropical forest on the northeastern side of Costa Rica and is a couple of hours by car or bus from San José.

Guests at the station are provided with rooms (three to a room, usually) and three meals per day. The food was typical Costa Rican: lots of beans and rice, and a bit of meat and veggies, with vegetarian options if you wanted it. It certainly wasn't a gourmet experience, but they never served anything I didn't like, and if you've been hiking in mud for a few hours, anything tastes pretty good. There's no alcohol available from the station, but we all stocked up on what we thought we'd "need" before the left San José.

We were there over the New Year, which is near the end of the rainy season (and it sure rained a lot while we were there), so there was a lot of mud. A few of the main trails from the station are paved with concrete, so even if the mud is hopelessly deep, there are many kilometers of concrete trails that can be easily walked. We tried to search for caterpillars in as many places as possible, and it was easy to walk on the concrete and step off into the mud for a couple of meters to examine a plant for caterpillars.

The fact that it rained most of the time wasn't a real problem: the rain is relatively warm and the outside temperature is also, so you are just wet a lot of the time. It wasn't really necessary, or even wise, to put on dry clothes since almost the minute you stepped outside, they'd be wet again. I usually just put on damp field clothes every morning, and even if they had just been washed, they tended to be still wet since nothing dries very fast in 100% humidity. In fact, one team member had on a cotton t-shirt the first day, hung it up for the rest of the trip, and not only was it not dry at the end, but it was covered with mold. Such are the tropics.

The plants that are likely candidates for caterpillars are those with damaged leaves and, depending on the plant, certain kinds of damage indicated the likely presence of caterpillars. But basically 100% of the old leaves were damaged in some way, and finding the caterpillars is much more difficult than it might seem. We were usually in groups of three or four people, and it was not uncommon to come back from a few hours of looking where one person had zero finds. There were nine of us Earthwatch volunteers and four others who went out on most days for a morning or afternoon hike, and after about 6 full days, all of us together found about 300 caterpillars.

Another problem is that most of the caterpillars are small. Many are so small that they are easy to miss without looking very carefully at the bottom of a leaf. They tend to be cryptically colored so they are almost invisible (to hide from predators like birds, frogs, other insects, monkeys, and Earthwatch volunteers).

Most of the searching was from the concrete trails, but on the next-to-last day almost all of us spent most of it on muddy trails, which was "fun." The "fun" is in quotes, since it's really what a good friend of mine refers to as "type-two fun;" something that's not fun at all, except when you get to tell and re-tell the story for the rest of your life. We had a few type-two fun experiences on this trip, but if you really want to know about type-two fun on an Earthwatch expedition, read my story about a project to study butterflies in Ecuador.

We all wore rubber boots that come up to just below the knee, and they're great: you can step in water or mud usually without worrying about going in over the top. They're relatively cheap: maybe $10 to $15. I got a pair that are a bit too big, and then wore thick wool socks to fill them up. The thick padding made blisters hard to get (I got none) and it was easy to step into and out of the boots. When we went into the dining room or the dormitory rooms we'd just kick off the boots outside to keep the mud outside. There were a couple of boot-washing stations available with running water and a brush if there was really a lot of mud. Since the boots are relatively cheap, I just donated mine to a student at the lab when I left, and that allowed me a lot more extra space in my suitcase for the trip home.

One disadvantage of boots that are relatively easy to get on and off is that they are relatively easy to get off. On one hike on a muddy trail I stepped on a spot that was a bit deeper than I thought (but not deep enough to go over the top of the boot) and when I lifted my foot, the boot stayed where it was and the foot came out. That put me off balance, and to avoid falling, I put the foot back down, but not in the boot. My whole sock was covered with mud, which I had to put back into the boot for the rest of the hike.

The most important reason for the boots is, of course, snakes. There are a lot of poisonous snakes at La Selva and some can be agressive. See the story with the last photo at the bottom of this page for a couple of examples of type-two fun.

Butterflies or Moths? (or Skippers?)

Most people see a big difference between butterflies and moths, but in a sense, the division is somewhat arbitrary. The situation is in flux (see below) but there are currently recognized to be 127 families of order Lepidoptera, 5 of which are called "butterflies." The members of one family (Hesperidae) are called "skippers," and all the rest are called "moths."

What we call moths are considered usually to have feathery antennae, and their wings tend to be held at rest more parallel to the ground. Butterflies tend to have antennae with a bump at the end and to sit with their wings together and perpendicular to the ground. The skippers are in between, with butterfly-like antennae and moth like wing positions. The skippers and butterflies do form a nice superfamily, but all are Lepidopterans. The rest of the moths are also divided into superfamilies as well.

I guess one of the problems that taxonomists have is that the original idea of dividing all living things into these groups: kingdom, phylum, class, order, family, genus, species, is that sometimes you need a lot more subdivisions and sometimes fewer. An extreme example of needing fewer divisions is the Ginkgo tree (Ginkgo biloba), which is the only member of its phylum.

Here's a list of the Lepidoptera families, at least as of this writing.

In any case, we were interested in all of them.

When I said the situation is in flux, I don't mean that we can't sort out the butterflies from the moths, I mean that as more DNA evidence is examined, all sorts of previously-believed relationships have changed. Species that were thought to be closely related based on appearance and other things are found not to be and vice-versa. New families are created and sometimes old ones are merged.

This chaos is not restricted to Lepidoptera: it is occurring in basically all fields of biology. I'm pretty interested in birds, and I did some birding when I had time off, and found that a few of the bird names I was used to had changed. For example, one bird, previously known as the "Chestnut-mandibled Toucan (now Ramphastos ambiguus swainsonii; was Ramphastos swainsonii)" was discovered to be identical to a species in South America, and now has the name of the South American bird: the "Yellow-throated Toucan." There were other name changes as well.

When evidence indicates that two previously-named species are the same, one of the names is eliminated and they are said to have become "lumped." When the opposite occurs, and the one species turns out to be two, they are "split." In Costa Rica, for example, there used to be a species of Tanager called the "Scarlet-rumped Tanager (Ramphocelus passerinii)," but there were two populations, one on each side of the country, and it was decided that they were different enough to be considered two. Now there is a Passerini's Tanager (Ramphocelus passerinii) on the La Selva side and a Cherrie's tanager (Ramphocelus costaricensis) on the southwest (Pacific coast) side of Costa Rica.

Some taxonomists tend to like to combine species and some like to split them. They're called "lumpers" and "splitters," respectively.

The Daily Grind

When we first arrived, we had collected zero caterpillars, so the only thing to do was to begin the collection. As the days went on, however, there were more and more caterpillars, so a larger and larger portion of the work involved taking care of the ones that we had captured.

Caterpillars are basically highly inefficient eating machines. They eat leaves and as the leaf material passes through their gut, some small fraction of the leaves' material is incorporated into caterpillar flesh, but the majority comes out the rear end as "frass" which is just caterpillar shit. We volunteers were of course quick to exercise our linguistic abilities with the creation of such phrases as "frass-head," et cetera.

Anyway, each caterpillar lived in a plastic bag with (hopefully) enough leaf material to eat until it pupated, but every day it was important to check the bag, clean out the frass, and check to make sure the caterpillar was still alive, or if it had pupated. This activity was called "zoo."

Every morning some volunteers did zoo for at least a while, while the others went out collecting. On the very last day (which was just a half-day, since we got on the bus after lunch to return to San José) it took all of us to do zoo and to help with packing of other research materials. One person had volunteered to say for an extra week to do zoo after we left. His job would get easier and easier as the caterpillars died, pupated, or eclosed (emerged from the pupa).

In addition to the zoo, the expedition leader wanted us to take photos of all the caterpillars: a dorsal view, a lateral view, and a view of the "face." As I said, most of the caterpillars are pretty small, so all the photography was done with a nice macro setup: a DSLR camera with a high-quality macro lens equipped with a flash unit attached to the end of the lens. With the flash, we could stop down the lens quite a bit to get a better depth-of-field, and we got some pretty good shots although to get them often required a lot of patience, since the caterpillars were often not very cooperative and squirmed around a lot. The hardest ones to shoot were the Geometrids (inch worms) since they seemed to lay flat for only an instant before they looped up again. When they were flat, it was easy to get a good dorsal shot, but when they were looped, some part of them was always out of focus.

There are some photos very much like the ones we took and of similar caterpillars at which is maintained by the leader of our expedition.

Usually we'd do zoo and collecting in the morning, have lunch at the station, and then all of us would do collecting in the afternoon. On the next-to-last day we took bag lunches since we wanted to collect on trails farther from the station, and couldn't make it back in time for lunch.


Usually the collecting was done within a couple of meters of a concrete trail. You'd find a plant with damaged leaves (almost all plants were candidates in this respect), and then you'd look over the bottoms of the leaves, one at a time. Sometimes the caterpillars were just there, but often they'd be hiding in a rolled-up potion of the edge of the leaf, or they had folded over the edge and were under that. If there was frass on the leaf, that was a good clue that there was a caterpillar present.

It was always a bit exciting to unroll or unfold a leaf since sometimes there was a caterpillar inside and sometimes other things like spiders or ants. But usually they were empty.

If you are off-trail it is a good idea to avoid brushing against any vegetation, if possible. Some of the palm trees are covered with needle-like spines, and some trees and plants have ants on them that you might brush onto your clothes. Lots of ants have nasty bites, but the nastiest in Costa Rica, at least, is the Bullet Ant. It's an ant that's about an inch long, is closely related to wasps, and still has a wasp-like stinger in addition to a bite. I've never been stung, but have heard that a sting is like being injected with sulfuric acid and then twisting the needle for a few hours. I did have a bullet ant brushed off on me this trip but another volunteer spotted it and brushed it off! The name comes from the fact that a sting feels a lot like a bullet going in.

One section of the trip report for the 1998 version of this trip has a section on Bullet Ants, since part of that project was to study what protections caterpillars had against these predators.

The spines on the palm trees were particularly bad news in slippery mud. If you slipped and felt yourself going down, you often grab at something to keep from falling. If you grab a spiny tree, you'll wind up with a bunch of spines buried in your hand. One of the volunteers had this happen on a steep muddy trail.

Being off-trail in the mud is a lot of work: there's always something holding you back: vines, mud, fallen trees, et cetera. You'd take a couple of steps and then re-evaluate your strategy, over and over. I wear a watch that automatically counts my footsteps, and it "knows" that I'm walking if I take a bunch of steps in a row, like 10 or 15 of them. But if I just take one or two, it doesn't count them, and doesn't think I'm getting any exercise. If it notices that I haven't taken any steps for a while (not counting the sequences that have fewer than about 10 steps) it lets me know that I should get some exercise by beeping and displaying the message "MOVE" on the watch face. Once when I had been off-trail in the mud for a while, struggling with mud and vines and downed trees, looking for caterpillars, I got the beep and the "MOVE," which was a little discouraging.

All in all, I had a great time, and I think most of the other volunteers did, too. We all got along pretty well, and everybody was willing to do whatever was necessary to get the job done.

Photos and Videos

I didn't take any photos of our chief target: the caterpillars on my own camera when I was there, but if you want to see some examples of things that we did catch, you can look at my trip report from 1998 or at Most of the photos below were shot on an iPhone.

There were dozens of Collared peccaries (Pecari tajacu), also known as the Javalina, who spent most of their time at the La Selva station. When it was raining, a large group of them would sleep in the shelter of one of the laboratory buildings, all packed together. Here's a video of a mother nursing her baby.

This is a Crested Guan (Penelope purpurascens). We saw a fair number of these at the station.

Here is the one fairly good bird photo I took. It is the female White-collared Manakin (Manacus candei). The male looks completely different, and does have a white collar.

Here is some species of Praying Mantis (maybe Choeradodis sp.) that I found on the wall of one of the research buildings.

We were looking for caterpillars in the Successional Plots and found this snake up in a tree. I have no idea what it is exactly, and nobody felt like poking it to find out. The head is obviously hidden.

Just a few minutes after we found this one, I stepped on a palm frond that had fallen on the ground, and a snake came out from the other end of the frond. It was mostly interested in getting away, so it squirmed into the underbrush, but it was obviously a Fer-de-lance (Bothrops atrox): a snake that is pretty poisonous and fairly aggressive. It's also known as a "Terciopelo" (which means "velvet" in Spanish) or an "Equis" (which means the letter "X" in Spanish). I don't know about the "velvet," but the "X" makes sense: the pattern on the snake's back looks like a series of the letter. Here are a bunch of photos of typical examples.

You can find a lot of Poison Dart Frogs at La Selva, and they are usually colorful tiny frogs, but the bold colors advertise the fact that they are poisonous. We saw a bunch of those, but I didn't get a photo. (But there is a photo of one in my 1998 trip report.) These, on the other hand, are much larger and they are all made of colorful plastic. Maybe it is somebody's "art," but they could also be part of some actual research. Note that at least the two of them on the bottom of the photo seem to have wires coming out of their butts (click on the image to the left to see a larger version if you can't see the wires). Maybe there's a device to measure temperature or something else inside.

This is the Smokey Jungle Frog (Leptodactylus pentadactylus). When we were walking around at night these were fairly common.

I had read about this before, but had never seen an actual example. It is an ant infected by a fungus that affects the ant's brain in such a way that it causes it to climb up to a relatively high point and die. Then the fungus grows out of its head and "flowers," spreading the spores over a larger distance because they are dropped from a height rather than right on the ground. The scattered spores may then attack other ants and the process continues.

Usually when we found caterpillars we would find a single one, but here's an example where a large group of them were found on the same leaf.

On our day off, a bunch of us hired a local guide to show us stuff in the rainforest: birds, plants, insects, mammals, whatever. Here is a Keel-billed Toucan (Ramphastos sulfuratus). The photo was taken on an iPhone through the eyepiece of a spotting scope. The method is called "digi-scoping."

Still with the local guide, here's a photo of a nut related to the common nutmeg that we use as a spice. The common nutmeg is surrounded by another spice called "mace." The red material here corresponds to the mace, and it wraps around the nut corresponding to the nutmeg.

The most exciting thing that happened was on the next-to-last day. We were out on a very steep and muddy trail. It was so steep and muddy that I, who has fairly bad balance, fell on my butt four or five times on the descents. Luckily the landings were all soft: into mud.

Anyway, we were walking down the trail with the project leader (Lee) in the lead, and he bumped into a "vine" that was hanging down in the middle of the trail. Well, it wasn't a vine, it was an Eyelash Viper (Bothriechis schlegelii) which is related to Rattlesnakes, Fer-de-lances, et cetera, and it struck at him, luckily hitting the shoulder strap on his backpack instead of his face.

It then curled up into a defensive position, ready to strike again, and it was obviously totally pissed off. I got this photo which is a bit misleading. In the usual darkness of the rainforest under the canopy, the snake appeared to be brown, like any self-respecting vine, but it was so dark that I used the flash on my iPhone, and the red-orange color came out in the photo.

Probably one of the reasons Lee didn't see it is that it's always a good idea to look at the ground ahead as you are walking in steep slippery mud. In fact, a few hundred meters along on our walk we found a Fer-de-lance coiled up in the center of the trail. Good times!

Follow up: Well, this was what I thought happened, but it turns out, on looking closely at the various photos of the snake (everybody there took them) that the snake was not an Eyelash Viper, but was instead an arboreal Boa (which is not poisonous). But if you erase this final paragraph, that was the situation as we saw it when we continued on our hike after the encounter. In retrospect, most Eyelash Vipers are yellow or green, but they can be reddish, too. Here are some Eyelash Viper photos.

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