Caterpillar Anatomy

How can you tell if you've found a caterpillar or a worm?
Caterpillars are multi-segmented with an identifiable head capsule, thorax, and abdomen.

Caterpillar 101

In the spirit of Henry David Thoreau, I went into the wild of Southeast Arizona, in search of caterpillars, to "discover some essential facts about life" and to more fully live.

After a tough year teaching in urban Los Angeles, I needed a new perspective and to immerse my self in the mysteries of the natural world, and to have a great adventure. I wanted to know how studying something so small could be so significant. I also wanted to live scientific investigation 24/7 to better understand the process, discipline, and documentation to become a better more informed science teacher.

This is a friend who kept me company while I entered our research data.

I had no idea how much there was to learn about lepidoptera, caterpillars and other life stages. On the expedition I got a glimpse of how complex and mind expanding studying caterpillars could be. Every day was filled with wonder as I had time to focus on their micro universe.

Here are some basics. First, there are around 119 known families of lepidoptera. As we all know, they have four life stages, egg, larval, pupal, and adult. This project focused primarily on the larval phase. As larvae, lepidoptera are basically feeding tubes with a mouth, foregut, midgut, hindgut, and anus. Caterpillars eat and poop a lot. (I also learned that caterpillar poop is called frass and finding frass is a clue to predators and amateur lepidopterists, like myself, that caterpillars are near.) They hang out in the larval phase for a few weeks, some a little longer. They spend one week to a few months in the pupal stage depending on the species and season. Adults do not live long. The main goal of a butterfly or moth is to reproduce and lay eggs.

Predators of caterpillars include birds, reptiles, amphibians and mammals. Insect biomass makes up a large part of terrestrial, above ground, ecosystems, and, as Dan Jansen said, caterpillars are “the hamburger of terrestrial ecosystems.” Micro and sometimes unseen predators of caterpillars are hymadoptora (wasps) and dyptora (flies). More to come about these parasitoids.

These are pictures of a geometrid I found while beating an alligator juniper. Geometridae is the second largest lepidoptera family in North America. They are the most abundant as larvae, but are hard to find as adults. Can you identify this caterpillar's adaptation and see how it helps it to survive? I don't think I would have spotted this one if it hadn't dropped on my beat sheet.

Can you see another species of geometridae in this picture? Not only do they camouflage with color and shape but with their behavior and posture. Geometrids remain "cryptic" during the day and mainly feed at night. Geometrids like this one will hold this position, disguised as a leaf petiole, for a very long time. The geometrid grips the stem with its front legs and anchors its end, seemingly unattached, with a thin thread of silk from its abdomen. This guy has amazing adaptations for survival!

Night Light Trap off Portal Road, Aug 6, 2011

It was a dark night of solid cloud cover that hid the moon and every star. A perfect night for a light trap. I rode in the jeep thrilled with adventure. Visibility was low, the road rough, and the vehicle dipped and splashed through through washes that flood this time of year occasionally leaving Portal Road impassible. Small critters darting across the road made me wonder about all the wildlife invisible to me in  the vast darkness. Road conditions made for a long four miles. 

Finally we spotted two light traps from the road that were set up by other lepidopterists of our project. Lepidopterists are scientists who study the lives of moths and and butterflies. Traps were set to collect adults of the species being studied. Some females are collected in hope that they will lay eggs and the entire natural histories of undocumented species can be photographed and studied. This is the work of Dr. David Wagner, author of Caterpillars of Eastern North America : a guide to identification and natural history / David L. Wagner. Princeton, NJ : Princeton University Press, 2005, and professor of Entimology in the department of Ecology and Evolutionary Biology at the University of Connecticut. http://www.eeb.uconn.edu/people/dwagner//. Dr. Wagner, also know as Wags, is beginning to work on a Princeton guide of the western U.S.. Some of our field work will be featured in his book!         

I'm studying species on the sheet. The light is mounted on a tripod and hooked up to a generator. The mercury vapor light shines brightly on a hung sheet to attract insects from a distance.

A black light attracts insects from near proximity.

Anyone close to the light provides a landing pad.

More Adventure off Portal Road, Aug. 6, 2011

 I found this millipede crossing my path. When I picked it up, it rolled into this protective coil. This millipede has the adaptation of strong armor like panel segments on its back so it is hard yet flexible. Because of the smallness of segments it can instantly coil to protect its many legs and vulnerable underside.

       Barrel cactus ready to bloom. Many cacti are pollinated by moths.

 This sparrow nest was spotted by Lynn as she was looking for caterpillars. The nest is well protected at the heart of an ocotillo, which has extremely sharp inch long spines camouflaged in those soft fluttery leaves. These spines are the plant's adaptation to protect itself and many desert birds take advantage of this spiny desert plant's adaptation. Can you think of other adaptations of plants that benefit other species?

Completely satisfied, even though I was sweaty, covered with tiny biting blackflies and out of water, we loaded our ice chest with at least fifteen different species and host plant matter to bring back to our zoo.

Back at the lab I was able to take a closer look at two arctiideas I found. 

Angela Smilanich, of University of Nevada and Desert Research Institute, explained to me that these two are the same species of arctiidae. The one with the black tufts is a 5th instar and the fatter one on bottom is a third instar. An instar is a larval stage. When a caterpillar hatches, it is in its first instar. Each time it molts, sheds its skin, it changes to the next instar. Caterpillars have 5 instars before they pupate. (And yes, this is the one with the spiny hairs that probably stuck in my skin.)

First Full Day of Caterpillar Collecting, Aug. 6, 2011

I awoke early and headed out with a team of five Earthwatch volunteers to collect caterpillars off ocotillo and brush on Portal Road. As we drove away from the lush ecosystem of Cave Creek into more of a desert landscape I knew immediately of the need to get there in the cooler morning time. Excited to see just what type of caterpillars would hang out in this climate, I put my beat stick and beat sheet to work.

 The best way to find caterpillars is to hold a beat sheet, a square of canvas with a wood frame, below a branch and whack the branch with a strong stick. The I search the quadrants of the sheet, full of fallen plant matter, for any larvae. Some the caterpillars I look for are 3 millimeters long, so it is a real practice in patience.

 You can see how small they can be. This larva is in the arctiideae family; it's tiger moth caterpillar. Those black tipped projections that make it look like a miniature vacuum roller are called tufts; this one also has long needle- like hairs on its head and end that can stick a predator. I picked one out of my knuckle, and I'm glad it didn't hurt. I later learned that these hairs are venomous and it is a risky to handle them. Ah, sweet timing!

  To have better luck with a beat sheet, it helps to look for leaf damage. Even some bird predators look for signs that a caterpillar is feeding on a plant's leaves to know where to find lunch.

Welcome to Southeast Arizona, Aug. 5th, 2011

On the way from Tucson to Cave Creek Ranch I traveled through beautiful Sonoran Desert with saguaros, ocotillo, and creosote. This is the monsoon season in Southeast Arizona and the desert landscape is green and full of life. 

From the van I saw varying weather patterns across the vast horizon. In the distance were distinct pockets of lightning and localized rain. I saw at least five different types of clouds at a given time. Weather changes quickly from bright sun and dry heat to dark, cooler monsoon.

                                                   How many types of clouds can you see?

As we drove rocky dirt roads over hills and washes I saw the landscape grow intensely green and lush. The Chirichaua Mountains dramatically appeared and the land took on a whole new dimension. 

After a three-hour drive (the last 45 minutes traveling at about 25 mph) we arrived at Cave Creek Ranch. I stepped out of the van and immediately sensed how special this place really is. The air around me vibrated with the wings of over twenty hummingbirds. (I soon learned that there are thirteen known species here at the Ranch.) Birds of all types, colors, and sizes, with various songs filled the air around the front porch of the main office. We quickly checked in and prepped for our first collection.

            My first caterpillar is from the Geometridae family. They are commonly called inchworms. 

            We record the location, date, caterpillar family, quantity, and host plant on collection bags.

Night Observation/Collection Begins

 “I wear my sun glasses at night” . . . so I can snuggle various sphinx moths. The night-time light trap uses a mercury vapor lamp which is incredibly bright so I was advised to protect my eyes.

   

Why should we study caterpillars? Introduction Aug. 5, 2011

Climate change affects the number of caterpillars there are. Climate impacts parasitoids. If there are not enough parasitoids, there are too many caterpillars and plant bio mass decreases and the community structure changes.

“It is irresponsible to not study climate change and loss of biodiversity.”

     -Dr. Lee Dyer

Leading my Earthwatch expedition is biologist Lee Dyer from the University of Nevada. Lee has been working with Earthwatch volunteers studying biodiversity and climate change since 2002. Lee briefed us on the project by teaching terms for what we would observe. Here is a small part of what I learned. I will collect over 100 caterpillars. Our team will study multitrophic interactions. Studying multitrophic interactions means to study food chains, i.e., who eats who. Specifically we would be looking at tritrophic interactions, interactions between three types of living things: plants, caterpillars, and parasitoids. A parasite is a life form that lives off of another life form, like fleas on a dog. A parasitoid is a parasite that actually kills its host over time. Wasps and flies are the parasitoids whose eggs and larvae grow in caterpillars.

The parasitoid feeds off the host caterpillar and then bursts out of the caterpillar body as a larva or even an adult! The parasitoids of the project have ovipositors, which are modified stingers that females use to lay their eggs. Wasps have hard, piercing ovipositors that inject eggs into soft caterpillar bodies. Along with eggs, wasps may also inject viruses or toxins that make it hard for a caterpillar’s immune system to kill the eggs or kill the larvae once they hatch and begin to feed on them internally.  So, we will go out to collect caterpillars, put them in Ziploc bags with their plant material, take macro photos and data, and then feed and maintain them in our “zoo” (lab). Over time we will watch and see the internal parasitoids appear. 

 “The major goal of the project is to measure tritrophic interaction diversity: species richness, evenness, abundance, species turnover, keystone species.”