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INSECT RELATIVES -- CLASS ARACHNIDA

Spider mites are microscopic or nearly microscopic animals with two body regions and four pairs of legs. They do not have antennae. Some common species are the two-spotted or red spider mite. These mites have two spots on the back and have tail-end spots in some species. They may be clear, orange, or reddish. The clover mite is reddish brown or grayish, and are flat with long front legs.

Some mites are beneficial because they feed on plant mites. Predatory mites occur on infested plants, but are larger than their prey and move more quickly. Some may be purchased for biological control.

Spiders resemble spider mites, except they are larger and have two clearly distinct body regions with a thin waist between. Most spiders are predators of insects, and thus are beneficial.

One common poisonous species is the black widow spider. Black widows are shy and like dark places. They spin a characteristically messy web. They are shiny black, moderately sized spiders with a reddish or orange hourglass marking on the underside of the abdomen. Males and immature females can have stripes of red, yellow, and black on the abdomen.

Ticks are larger than mites and are important because they are parasites of man and animals. The most prevalent tick in Arizona is the brown dog tick. It is specific to dogs and can develop infestations in kennels, backyards, and inside homes. This tick is not known to transmit human diseases.

Scorpions have two body regions, the cephalothorax and the abdomen. The abdomen is elongated into a "tail" which ends in a bulbous segment called a telson. The telson contains the stinger. Scorpions are active at night, feeding on insects such as cockroaches or house crickets.

OTHER CLASSES

Millipedes (Class Diplopoda) are elongate invertebrates. They are generally round in cross section and, with the exception of the first four or five, all of the body segments possess two pairs of legs. They are relatively slow moving, and feed on fungus and decaying plant material. At times, they can be a pest to vegetables or other plants in greenhouses.

Centipedes (Class Chilopoda) strongly resemble millipedes. Their antennae are longer, they are more flattened in cross section, they have one pair of legs per body segment and they can move rapidly. They are beneficial in that they are predators of other arthropods. Centipedes are nocturnal and actively seek dark shelter if exposed. The first pair of legs possess venom glands, which they use to subdue their prey.

Sowbugs and pillbugs (Class Crustacea) are oval with a hard, convex outer shell made up of a number of plates. Sowbugs are highly dependent on moisture, which accounts for their common association with damp habitats. Generally, they feed on decaying plant material. They will occasionally feed on young plants in greenhouses and gardens but impact in these situations is minimal.

Garden centipedes or symphylans (Class Symphyla) look like tiny centipedes, except they have 10-12 pairs of legs. They are not common and live under stones, in damp soils rich in organic matter, and in rotting wood.

Phylum Mollusca - Slugs and Snails Slugs and snails may also feed on plants and cause damage similar to that of insects. These creatures are found in moist conditions so they aren't common in Arizona, but can build up in places that are watered frequently such as greenhouses and nurseries. Slugs and snails leave a shiny trail of mucus behind themselves, which is a sure sign that insects are not the culprit.