text: why does customs not allow fruit to be taken from country to country?   fruit shipments can contain insects or parasites which are not native to the country of destination. when organisms are introduced to an ecosystem, there are not levels in place to ensure that the balance is maintained. for example, some exotic fly wouldn't be population controlled because no native spider is used to eating it. this uncontrolled population growth of invasive organisms can upset the balance of the food chain, or destroy entire crops.