that make them unpalatable to predators (Dyer, 1997; Hero et al.,
2001; Smith et al., 2012). Many of these organisms, such as monarch
caterpillars and poison dart frogs, are brightly colored (aposematic) to
warn predators not to attack them (Smith, 2000; Campbell & Reece,
2004; Inbar & Lev-Yadun, 2005). Palatable species like inchworm
(geometrid) caterpillars use camouflaging colors and morphological
mimicry to blend into their surroundings (Campbell & Reece, 2004;
Smith et al., 2012). These species are found on plants with features that
match the caterpillars’ camouflage patterning or morphological mimicry (Campbell & Reece, 2004; Smith et al., 2012). Others have
adapted to live on a certain part of a plant, such as under the leaf, near
the ground, or higher in the canopy (Tvardikova & Novotny, 2012).
Predator species also specialize by foraging on a particular plant species,
on groups of species ( i.e., deciduous or coniferous trees), or on locations within a plant (MacArthur, 1958).
Caterpillars are important prey species because they are abundant
and diverse in many ecosystems, play a vital role in food webs and
nutrient cycling, and support a rich community of parasitoids and
vertebrate and invertebrate predators (Stange et al., 2011; Poch &
Simonetti, 2013). For example, caterpillar densities and abundance
affect behavior and reproductive success of breeding birds (Moorman
et al., 2007; Townsend et al., 2016). Predatory invertebrates and small
mammals will also eat caterpillars (Ostfeld & Keesing, 2000; Hooks
et al., 2003). Therefore, caterpillars are an ideal study organism to
investigate interactions among predators and prey.
Direct assessment of predation on caterpillars is challenging
because it is hard to track live caterpillars in natural habitats, making
it nearly impossible to determine whether predation occurred. Thus,
plasticine model caterpillars offer an excellent alternative for quantifying relative predation rates by birds, small mammals, and invertebrates (Howe et al., 2009; Low et al., 2014). Plasticine is a soft
modeling clay that does not harden over time and is available in a variety of colors. Many predators are initially fooled by plasticine model
caterpillars, and a durable legacy of their attack is imprinted in the
plasticine. Examination of recovered models after attack yields
impressions left by teeth, beaks, or mandibles of predators.
The goal of this experiment is to introduce students to the scientific
method using hands-on experiential learning. Students will follow
the scientific process, beginning with asking questions through
making conclusions and considering future research. Predator–prey
interactions will be assessed directly by observation of predation
marks on plasticine model caterpillars. Through their questions,
students will investigate whether factors such as color or location
drive predator–prey dynamics.
Setup & Plasticine Model Caterpillar
The first step is to have students develop specific questions that use
plasticine model caterpillars to investigate predation. Teachers can
provide students with a topic or prime more independent investigation with a few options to help them along (Table 1). Questions
could evaluate aposematic vs. cryptic coloration, location of larvae
on plants, different habitats or locations, and more. Independent
variables ( i.e., location, height, plant, color) and dependent variables
( i.e., predation rate for each type of predator) should be determined
for their question. They should also develop a hypothesis, prediction, and experimental design to address their question (examples
in Table 1). These steps let students work through questions 1–4
of the assessment that accompanies this lesson (Appendix 1).
Plasticine (or plastalina) can be found in most craft stores. Lengths
of plasticine should be rolled out to ~3.5 mm in diameter, and cut to
~25 mm lengths to mimic the size of some caterpillars while still being
large enough to handle (Figure 1). Each piece of clay should be bent
slightly in the shape of an arc to simulate a geometrid (inchworm) caterpillar. Other sizes, shapes, and colors can simulate different types of
caterpillars depending on the students’ questions. To prevent inadvertent damage and marking to the plasticine model caterpillars, they can
be transported in Tupperware containers divided by layers of wax
paper. Some plasticine model caterpillars will get marked by fingernails
or dropped during deployment, so it is important to have extra models
on hand. The number of plasticine model caterpillars attacked by predators can vary substantially. Several studies report predation rates of
15–30%, although lower (e.g., 5%) and higher (e.g., 50%) predation
rates have also been observed (W. Leuenberger, unpublished data;
Ruiz-Guerra et al., 2012; Bereczki et al., 2014; Roslin et al., 2017).
Thus, deployment of ≥50 plasticine model caterpillars should be considered for meaningful assessment of predation attempts.
Superglue is used to affix plasticine model caterpillars to vegetation. To limit mess, we recommend using a gel control variety of
superglue, and instructors should have nail polish remover to clean
Table 1. Sample hypotheses, experiments, and predictions for plasticine model caterpillar experiments.
Hypothesis Prediction Experiment
Caterpillar color affects
Camouflaged caterpillars will suffer higher predation than
aposematically colored caterpillars.
Set out green and red caterpillars.
Plant type affects
Caterpillars on shrubs will have higher predation than
caterpillars on trees.
Place caterpillars on trees and
Caterpillars in an open area will have higher predation than
those placed in the forest.
Deploy some caterpillars in a forested
area and others in an open area.
Predation is different
for caterpillars placed
at different heights.
Caterpillars located 0.5 m above ground will experience
greater predation than caterpillars located 1 m above
Place caterpillars 0.5 m and 1 m