The stories of conquest and depredation of alang alang grass and gypsy moth show how serious the unfettered invasion of alien life forms (both zoological and botanical) can become. A native of South Asia, and a valued source of thatch, alang alang grass is a weed whose economic importance is outstripped by its nuisance. Once it is allowed to a get a grip on the land, "it does not let anything else grow there, and does not let depleted soil regain its fertility'. A part of the saga of deforestation from East Asia through Oceania, alang alang grass gets hold of the earth in logged areas of forests and stops trees from coming back, thus spreading deforestation. On the botanical side, the notorious gypsy moth is an equivalent of this grass. Spread over Eurasian forests as a pest, it was introduced in North America in the 1860s by Leopold Trouvelot, a French artist and entomologist. He had brought it in the vain hope to start a silk industry. The moth somehow slipped through his open window and colonised an entire continent. In the first major outbreak in 1889, it stripped Medford and its surroundings of foliage. Now it colonises an area from Maine and Quebec, to Michigan and as far as Virginia.