Hawaii is an important trading center and about six million tourists visit there every year. With all that traffic in and out, exotic species have plenty of opportunities to reach the islands. According to biologists, exotic species are the number one threat to the state' s economy, environment, and way of life. The question in Hawaii is, can the invaders be stopped? Quarantines are one way to do this. Quarantine is the process of isolating animals or products. In Hawaii, pet dogs and cats coming into the state remain in a special holding facility for four months to make sure they don' t have rabies( ) Many agricultural products are also quarantined to see if they are carrying insect pests or plant diseases. Inspection is a second way to stop biological invaders. At airports, borders, and shipping ports, inspectors examine passengers and their baggage to see if they are carrying exotic species. The inspectors also destroy fruits, vegetables, or other goods that might be carrying harmful pests or diseases. Specially trained dogs also smell goods in the ship for exotic species. What if an exotic species slips by inspectors? Then efforts are made to control the invader. In Hawaii,government agencies control invaders by setting  livetraps around wildlife shelters and other places. At Haleakala National Park employees have built miles of fences to keep out exotic pigs and goats. For years these animals ate and walked over native rain forest plants, hut the fences have helped reverse( )this damage. Now native plants grow in places that were bare rock only a short time ago. In some cases biological control helps to solve the exotic species problems. It is the science of controlling one invader with another. In the early 1900s, several exotic predators  were imported to Hawaii to eat a harmful exotic pest called the sugarcane leafhopper. The insect was destroying 70,000 tons of sugar a year ,but the predators brought it under control. The efforts of these scientists and other people are vitally important. In Hawaii alone,10,000 different species of native plants and animals still need to be protected. Many of these are found nowhere else on earth. By stopping the spread of the biological invaders, we not only protect ourselves, but we also protect the many other native species that make our planet such a special place to live. Hawaii is at a great risk of invasion by exotic species, because   _  .
many agriculture products grow there regular inspections of animals are useless millions of people go to Hawaii each year biological control efforts have not worked