An invertebrate is any animal without an internal backbone including insects, spiders, mollusks, crustaceans, and worms. 

Insects (Arthropods)

• Have three main body segments, three pairs of walking legs, and antennae 
• Live in the air, on and in soil, and in water
• Majority are harmless or even beneficial; less than 1% are considered pests 
• Aid in the production of fruits, seeds, and vegetables by pollinating blossoms
• Improve soil’s physical condition by burrowing throughout the surface layer 
• Some parasitize or prey on harmful insects
• Serve as food sources for birds, fish, mammals, reptiles, and other animals

Spiders and mites (Arachnids)

• Have two main body segments, four pairs of walking legs, and no antennae
• Spiders are generally beneficial because of the large number of insects they eat

Snails and slugs (Mollusks)

• Move by gliding along on a muscular “foot” 
• The “foot” constantly secretes mucus that helps them move and later dries to form the silvery slime trail