Are illegal aliens benefitting our nation? Well that’s certainly a heated debate among economists, but ecologists are now joining in a similar type of discussion regarding non-native plant and animal species which continue to invade our shores.  While environmentalists claim non-native species cost billions, other scientists contend these species have been a boon to our nation, as 99 percent of our food supply now consists of crop plants that did not have their origin in North America.  Indeed, even the highly publicized zebra mussel has been shown to have environmental benefits, as they strain algae and fertilizer runoff and have actually improved water quality sixfold since their arrival. Only time will tell whether these creatures truly deserve a green card.