Ross School - Senior Project 2008-09

Student: Grant Monahan

Mentor: Hugh McGuinness

Title: A Study on the Defensive Strategies of Lepidopteran Larvae on Eastern Long Island


For my Senior Project Hugh McGuinness and I conducted a scientific experiment in which we collected local caterpillars, and reared them for parasitoids. Parasitoids are species of wasps, flies, and nematodes that target caterpillars for egg laying. Parasitoids lay their eggs within the caterpillar's body utilizing the caterpillar for larval development, ultimately killing the host. Caterpillars also have many other predators including vertebrates and invertebrates that include birds, beetles, ants and wasps. Due to the fact that so many diverse predators that hunt in different ways, there is no general defense that protects them from all different types of predators. This leads to parasitoids targeting caterpillars that are highly defensive towards their vertebrate predators. This is because vertebrate predators would not only eat the caterpillar, but the defenseless parasitoid larvae. By targeting highly defensive caterpillars, parasitoids increase the survival of their eggs.


Paper 1, Paper 2, Image 1, Image 2

At the start of the senior project process my idea for a senior project was much different.  I was going to do a long distance paddle to raise money for the South Fork Breast Health Coalition.  Do to some self thinking and discussing the idea with my family I came to the realization that I wanted to do a more academic presentation.  All my life I have been interested in insects, and taking Entomology with Hugh McGuinness in the spring trimester re-sparked this interest.  In the beginning of July I emailed Hugh McGuinness to see if there was a possibility of an Entomology based senior project.  After some time McGuinness emailed me a project idea that consisted of a large-scale caterpillar collecting experiment, rearing each caterpillar for parasitoids, and writing a large literature review on caterpillar defense systems.  The collecting process was difficult because the caterpillars were extremely small, and required a trained eye to find.  After a few weeks I was able to locate caterpillars much easier.  Originally the collecting was supposed to be only of the Limacodidea family, but do to scarceness and time restraints we started collecting all families of caterpillars.  After some serious trouble with time management my collecting was behind schedule so in order to make up for lost time I had to write two papers, one on my collecting experiment, and two a literature review of caterpillar defenses.  This was my first time writing in the scientific style, and it became a grueling process.  The scientific style is a more condensed to the point writing style.  For my first draft I wrote an 8 page double spaced paper, and handed it in to McGuinness with a smirk on my face, I believed I had finished my senior project.  I was proven wrong when he handed me back a paper cover in red ink, and a 6-page single space paper about all my mistakes in my 8-page paper.  I was devastated, but after doing to edits I began to understand the scientific writing style more and more.  After 6 drafts I finally had the scientific style in my grasps, and was able to put my papers on display. 

Caterpillar defenses can be broken down into a three stage system: Stage 1: Not being seen, or warning potential enemies of harmful defenses, Stage 2: Once spotted, fighting back, and Stage 3: Once a parasitoid has successfully laid eggs inside to body, the immune system bombards the eggs cutting them off from vital nutrients.

Stage 1 defenses include cryptic coloration, feeding shelters, and warning coloration.  Stage 2 defenses include being unpalatable, hairs, spines, containing poison, use of osmeterium, thrashing, biting, and dropping.  Stage 3 defenses include encapsulation, and diet change. 

The main conclusion of my project was that there is no one defense to cover all types predators and enemies.  This is so because caterpillars have a wide spread range of predators that hunt caterpillars in diverse ways.  These predators and enemies include invertebrate predators that hunt uses traps and chemical cues, vertebrate predators that hunt using visual cues, and parasitoids that target caterpillars for larval development using chemical cues.  It seems that caterpillars have developed more defenses to protect themselves from vertebrate predators, making themselves vulnerable to invertebrate predators and parasitoids.  This leads to the idea that parasitoids target highly developed caterpillars to insure the survival of their eggs because a vertebrate predator would not only eat the caterpillar, but the developing larva inside. 

After doing this project I have seen how much a truly love evolutionary biology.  I feel that these skills I have gained will translate into college, and biology may become a future major. 

Works Cited

Brower L.P., J.N. Seiber, C.J. Nelson, S.P. Lynch, P.M. Tuskes.  Plant-Determined Variation in the Cardenolide Content, Thin-layer Chromatography Profiles, and Emetic potency of Monarch Butterflies, Danaus plexippus Reared on the Milkweed, Aclepias eriocarpa in California.  Journal of Chemical Ecology: 579-633.

Chan K., A. Lee, R. Oell, W. Etches, S. Nahirnial, S.M. Bagshaw, and L.M. Larratt.  2008.  Caterpillar-induced bleeding syndrome in a return traveler.  CMAJ: 179(2).

Chapman, R.F.  1998.  The insects: Structure and Function [Internet].  New York (NY): Pergamon Press; Available from:,M1.

Dyer L.A, and G. Gentry.  1999.  Predicting Natural-Enemy Responses to Herbivores in Natural and Managed Systems.  Ecological Applications, Vol.9, No.2:  402-408.

Dyer L.A.  1995.  Tasty Generalist and Nasty Specialist? Antipredator Mechanisms in Tropical Lepidopteran Larvae.  Ecology, 76(5): 1483-1496.

Dyer L.A.  1997.  Effectiveness of caterpillar defenses against three species of invertebrate predators.  Journal of Research on the Lepidoptera: 48-67.

Ehrlich P.R, and P.H. Raven.  1964. Butterflies and plants: a study in coevolution.  Evolution 18: 586-608.

Gentry G.L, and L.A. Dyer.  2002.  On the Conditional Nature of Neotropical Caterpillar Defenses Against Their Natural Enemies.  Ecology, 83(11): 3108-3119.

Heinrich B.  1979.  Foraging Strategies of Caterpillars: Leaf Damage and Possible Predator Avoidance Strategies.  Oecologia, 42: 325-337.

Holmes R.T., Schultz J.C., Nothnagle P.  1979.  Bird Predation on Forest Insects: An Exclosure Experiment.  Science, Vol. 206: 462-463.

Karban R., G. English-Loeb.  1997.  Tachinid Parasitoids Affect Host Plant Choice by Caterpillars to Increase Caterpillar Survival.  Ecology, 78(2):  603-611.

Leslie A.J., and M.R. Berenbaum.  1990.  Role of the Osmeterial Gland in Swallowtail Larvae (Papilionidae) in Defense Against an Avian Predator.  Journal of the LepidopteristsŐ Society, 44(4): 245-251.

Loeffler C.C.  1996.  Caterpillar Leaf Folding as a Defense Against Predation and Dislogment: Staged Encounters Using Dichomeris (Gelechiidae) Larvae on Goldenrods.  Journal of the LepidopteristsŐ Society, 50(3): 245-260.

Malcolm S.B.  Chemical Defense in Chewing and Sucking Insect Herbivores: Plant-derived Cardenolides in the Monarch Butterfly and Oleander Aphid.  Chemoecology: 12-21.

Marquis R.J and C.J. Whelan.  1994.  Insectivorous birds increase growth of white oak through consumption of leaf-chewing insects.  Ecology, 75: 2007-2014.

Miller, Rick [internet]. [updated 2009 January 12]. Iowa: Iowa State University Entomology Department. [cited 2009 Jan 13].  Available from:

Monahan G.  2008.  Levels of Parasitism on Lepidopteran Larvae of Eastern Long Island.  Unpublished Manuscript.

Rota J. and D.L. Wagner.  2008.  Wormholes, sensory nets and hypertrophied tactile setae: the extraordinary defence strategies of Brenthia caterpillars.  Animal Behavior.

Singer M.S, Y. Carriere, C. Theuring, and T. Hartmann.  2004.  Disentangling Food Quality from Resistance against Parasitoids: Diet Choice by a Generalist Caterpillar.  The American Naturalist, 164(3): 423-429.

Stamp S.E.  1992.  Relative Susceptibility to predation of Two Species of Caterpillar on Plantain.  Oecologia, 92: 124-129.

Turlings T.C.J., J.H. Loughrin, P.H. McCall, U.S.R. Rose, W.J. Lewis, J.H. Tumlinson.  1995.  How Caterpillar-Damaged Plants protect themselves by attracting parasitic wasps.  Proc. Natl.  Acad. Sci, 92: 4169-4174.

Wagner D.L., L. David. 2005 "Caterpillars of Eastern North America : A Guide to Identification and Natural History" (Princeton Field Guides) 496 pages.

Weiss W.R. 2006. Defecation Behaviors and Ecology of Insects.  Annual Review of Entomology, 51: 635-661.

Wheeler Q, and M. Blackwell.  1984.  Fungus-Insect Relationships [Internet].  New York (NY): Columbia University Press.  Available from:

Witz B.W.  1989.  Antipredator Mechanisms in Arthropods: A Twenty-Year Literature Survey.  Insect Behavioral Ecology: 71-99.

Community Member (Details)

John T. Lill is an assistant professor of biology at George Washington University. John T. Lill is also a caterpillar expert, and studies the co-evolutionary arms race between plants and the herbivore predators.