Pill Bug: an Isopod

Pill Bug: An Isopod

The pill bug (also called the wood louse and the roly-poly bug) is a small, segmented land creature that can roll into a tiny ball for protection. The pill bug is NOT an insect, but is an isopod (another type of arthropod).

Habitat and Distribution: Pill bugs are common invertebrates that are found in many biomes around the world, including temperate forests, rainforests, and grasslands. They prefer moist areas, often living in soil and under decaying leaves, rocks, and dead logs.

Life Cycle: A pill bug begins its life as a tiny egg. The young pill bug looks almost like a miniature adult. As it grows, it molts (sheds its old, outgrown exoskeleton) 4 to 5 times.

Anatomy: Pill bugs are covered by a hard exoskeleton (also called the cuticle) made from chitin. They have three basic body parts, the head (which is fused to the first segment of the thorax), the thorax (the 7 segments of the thorax that are not fused to the head are called the pereon), and the abdomen (which is also called the pleon). Pill bugs have 7 pairs of jointed legs and 2 pairs of antennae (but one pair is barely visible). The antennae, mouth and eyes are located on the head. A pair of abdominal uropods are at the posterior end of the pill bug, but only the terminal exopods are visible from the top of the pill bug. Pill bugs are less than an inch long.

Diet: Pill bugs eat decaying plants and animals and some living plants.

Predators: Pill bugs are eaten by many animals. Their main protection is rolling into an armored ball.

Classification: Kingdom Animalia (animals), Phylum Arthropoda, Subphylum Crustacea, Class Malacostraca, Order Isopoda (isopods), Family Armadillidiidae, Genus Armadillidium, Oniscus, etc. Many species, including A. vulgare (the common pillbug).

A.P. Biology Lab #11 Pill Bugs Page 129 Analysis 1. What conclusions do you draw from your data? Explain the physiological reasons for the behavior observed in this activity.

Analysis 2. Which type of environment do isopods prefer? How do the data support these conclusions. Give specific examples.

3. How do isopods locate appropriate environments?

4. If you suddenly turned a rock over and found isopods under it, what would you expect them to be doing? If you watched the isopods for a few minutes, how would you expect to see their behavior change?

5. Is the isopod’s response to moisture best classified as kinesis or taxis? Explain your response.

Student-Designed Experiment 1. Select one of the variable factors listed here and develop a hypothesis concerning the pillbugs’ response to the factor. (temperature, pH, background color, light or other)

2. Design the experiment.

a. State the objective. b. List materials you would use and why.

c. Outline your procedure in detail. Be brief.

3. Decide what data you will collect and design your data sheet.