Turning over the leaf of this radish plant, large and small green aphids are seen dining on the leaf.
Insects may hop, crawl or fly to your vegetable plants. Some insects, like the tomato hornworm and the cabbage root fly, seek only the vegetables after which they were named. The insects may eat the root, leaves or fruit of the plant. Some insects are large (the tomato hornworm I saw was the size of my little finger) and some insects are quite small, like aphids. Keep in mind that not all insects are pests. Ladybugs and bees are beneficial insects in a vegetable garden. For pictures and descriptions of vegetable garden insects, both harmful and beneficial, visit Texas A&M University Extension.
Deer, rabbits, cats, squirrels, dogs and some other four-legged animals can also be a garden nuisance as they may eat tender leaves or fruit, trample plants, dig holes, or defecate in the garden. Smaller animals, like mice or rats may also come to the garden for food. Of less concern are birds, which may eat fruit but then, birds also eat harmful insects. For a thorough description of potential animals that may be eating vegetable plants in your garden, see the University of California's Integrated Pest Management Program.
General control options
Preventing or eradicating pests varies depending on the plant being attacked and the type of pest. Some success in keeping annoying insects away from vegetable plants is accomplished by planting specific flowers whose scent deters bugs. In addition, a tall fence or bird netting may be the answer to send animals shopping elsewhere for a meal. In addition to the referenced Integrated Pest Management websites, your local university or college may have a county extension office through whom you can gain assistance. The services of county extensions are free and usually available by phone, email, or in-person at the extension office.