Antarctic nurtures only three flowering plants and not a single land vertebrate. The principal source of nutrients for the algae, mosses and lichens that make up the vegetation of Antarctica is the excreta of birds that feed in the seas and nest on the land. On this vegetation feed springtails and certain mites. This is the end of the food chain; there is no evidence that these inverterbrates are eaten by other organisms. This simple life cycle depends on the minimum of resources. On land, insects and arachnids constitute the hightest form of native life, half of which are parasitic. Man has not yet succeeded in introducing a new plant or animal into Antarctica, [6] nor does it appear feasible under the prevailing environmental conditions.