They are one of the most morphologically diverse of all the crustacean groups, coming in many different shapes and sizes and ranging from micrometers to a half meter in length. They also live in many different types of habitat, from mountains and deserts to the deep sea, and they are distributed worldwide. Isopods often do not look alike, but they do have common features. For example, all isopods have two pairs of antennae, compound eyes, and four sets of jaws.
The body, or pereon, of all isopods consists of seven segments, each with its own pair of walking legs. And to conserve water, they don't expel their waste through water-based urine, but directly into the air as ammonia. A sowbug Trachelipus rathkei at left and a pillbug Armadillidium vulgare on right with inset showing pillbug.
To cope with the problems of terrestrial life, the terrestrial isopods have a thick, hard exoskeleton where each body segment is topped with an armorlike plate that overlaps the plate on the section beneath. When disturbed, many of these isopods can curl themselves into a ball; this protects the softer underparts and appendages from attack and desiccation.
Pillbugs are the most successful at this activity, their common name referring to the fact that when curled up they resemble tiny pills. Unable to return to the water to breed, female isopods must carry water around with them. Fertilized eggs are deposited in a water-filled marsupium or brood pouch, located beneath the thorax.
When the eggs hatch, the young isopods, which resemble adults, must remain in the pouch until they can fend for themselves. Your habitat is now ready to do some experimenting.
Procedure Go outside and collect at least a dozen sow bugs or pill bugs. Only use one type of bug. To find them look under stones, decaying wood, old leaves, in gardens in the soil near plants, and along house foundations and basements.
You may need to look closely because they're small, can blend in well with their surroundings and might freeze in place when startled, making them harder to spot. Put an equal number of the little crustaceans in each carton meaning there should be at least six in each. Allow them to explore the cartons while you observe for at least 30 minutes.
How many bugs are in each carton over time? Does the carton that most of the bugs are in change over time? What other types of behaviors do you observe? Overall, which environment do the sow bugs or pill bugs seem to prefer, the one with damp or dry soil? Extra: Repeat this activity but compare different environments, such as leaf litter versus soil or small rocks versus small pieces of wood, etcetera.
Which environment do the sow bugs or pill bugs prefer in other environmental pairings? Extra: You could try to quantify your results from this activity. To do this, every five minutes you could count how many sow bugs or pill bugs are in each habitat. How do the numbers of these crustaceans in each environment change over time? Extra: You could do similar activities with other small, common animals, such as crickets, earwigs, ants, slugs, snails, mealworms and wax worms.
Crickets, mealworms and wax worms can usually be purchased at a local pet store whereas the other animals may be found locally by looking under rocks, garden plants, rotting logs and leaf litter. What type s of environments do these other animals prefer? If the animal you're using might be able to escape from the containers, be sure to secure a lid to them!
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