Class Chilopoda - Centipedes

Centipedes in Arizona range in size from one to ten inches. They are fast moving preditors with one pair of strong legs per body segment. Centipedes have fangs to inject poison and will attack animals larger than themselves.

Both centipedes and millipedes have a problem with water loss. Their exoskeleton does not have the waxy covering of other terrestrial arthropods. They are limited to moist environments and will usually be found in moist dirt under rocks and logs.

Class Diplopoda - Millipedes

Millipedes are slow moving with two pairs of small legs per body segment. They eat plant material and do not have poison glands.

Their bodies are more rounded than centipedes. When threatened, many of them will coil up to protect their softer underbelly.

Class Insecta - The Insects

The Two-tailed swallowtail, Papilio multicaudatus, is the Arizona State Insect.

Insects are today's most successful animals, inhabiting more habitat types than any other animal. Insects cause millions of dollars in damage in Arizona each year and millions more are spent trying to control insect pests. But insects are also beneficial. We could not do without the insect pollinators and we cannot overlook the importance of insects in the food chain.

The body of insects is divided into three segments:

• Head - Antennae and mouth parts are attached to the head.
• Cephalothorax - Legs and wings are atttached to the cephalothorax.
• Abdomen - There are no true appendages on the abdomen. The end of the abdomen is modified into an ovipositor or stinger in some insects.

Although we tend to think of insects as simple animals, their reproduction is quite complex. Study this website about the reproduction of Monarch butterflys. All insects go through a metamorphosis, a series of changes, from the time they hatch from the egg until they reach adulthood. One of the two types is complete metamorphosis.

• The larva that hatches from the egg looks nothing like the adult form. It has mouth parts and six segmented legs, although those legs are not obvious. The elongated caterpillar of butterflys and moths appear to have more than six legs. A close inspection will show that the "legs" toward the posterior end are not legs at all. They are fleshy projections that are not jointed. The larva feeds continually, storing energy for the pupa stage.
• The pupa is a period of apparent inactivity during which all the larva's stored energy is used to transform it into the adult form.
• The adult insect is characterized by having reproductive structures, and wings for flying insects. Some insects, like mayflys, do not have mouth parts and never eat during their short adult lives. They die shortly after mating and forming eggs.

• The nymph that hatches from the egg looks like a minature adult. Nymphs do not have wings or reproductive organs. It is transformed into an adult through several molts.
• The adult insect is characterized by having reproductive structures, and wings for flying insects.

Communication amoung insects is quite complicated. Most produce pheromones, a type of chemical messenger. Colony insects like bees and ants form a complex society.

Museum quality insect collections are stored to protect them from destruction by either humidity or live insects.

Here is a simple key of the Insect Orders.

Caterpillars only have six legs.
The other projections on the elongated body have no joints and are not legs.