A glimpse into Victorian ambitions for Ailanthus altissima, the Tree of Heaven

The specimen of Ailanthus altissima that stands along Meadow Road (forma erythrocarpa; 695-80*B) is a stately tree, its striking red fruits just coming into their summer glow. It’s also an example of one of the most prolific of introduced tree species. This plant was grown from cuttings made by Arboretum scientist Peter Del Tredici, taken in one of the species’ favorite habitats amid the gravel and drifting trash that lies between Interstate 95 and the Charles River in the metro Boston area. Described as “invasive,” Ailanthus is disparaged for the very characteristics that help it thrive in cities: it grows swiftly (a capacity we celebrate in other trees); it produces allelopathic chemicals that can inhibit the growth of other plants (the same is true of native black walnut among many other plants); it happily spreads by root suckers (like the pawpaw and the quaking aspen, to name just two), which spring up along fences and through pavement cracks.  

Ailanthus altissima f. erythrocarpa 695-80-B by Ned Friedman
Tree of Heaven photographed in flower in the Arboretum’s July landscape. Ned Friedman

I like to call Ailanthus a “feral tree”—a creature that has escaped the bounds of domestication. Breakout Ailanthus flourish in the city’s marginal spaces; in the urban wild of Bussey Brook Meadow, a grove of Ailanthus towers, slender-trunked and broad-crowned. They’re a far cry from the well-kept plants of the arboretum—or other domesticated creatures, such as Bombyx mori, the silk moth, grazing contentedly on mulberry leaves, as fluffy and flightless as the sheep it resembles in miniature. There is also a feral silk-making moth: Samia cynthia, known as the Ailanthus silk moth. Unlike B. mori, it is a free flyer, large, boldly marked, and charismatic. In south Asia, its cocoons are used to manufacture eri silk—a nubby, textured cloth, also called “peace silk,” as it is processed without killing the insects after the moths have flown from their cocoons (B. mori pupae are destroyed when the cocoons are boiled to extract the silk). And crucially, it subsists not on mulberry, but Ailanthus. 

Silk production had reached the Mediterranean world in the sixth century, but Bombyx mori proved too fragile for northern Europe, and attempts to establish silk production in England failed. As Ailanthus spread and thrived throughout cities in the nineteenth century, however, Victorian-era promoters envisioned a silk industry for northerly climes. “Much study has been bestowed on (Ailanthus and its silk moth) in Europe,” wrote a correspondent in London’s Journal of the Society of Arts in 1879; “so much so, that this study rejoices in the name Ailanthiculture, and the breeding houses of the insects are called Ailantheries.” In an 1865 issue of the Transactions of the Royal Entomological Society, Alexander Wallace describes his ailanthery: “I planted early in April 34 young trees of different ages, in 5 rows about 2½ feet apart…two died and two more made but little growth, but I had 30 trees of sufficient luxuriance of foliage to place thereon the young larvae.” Brimming with pride, Dr. Wallace invites visitors “to come in the morning before breakfast, and they will find the little worms spread over the under surface of the leaf feeding.” 

Ailanthus altissima by Frank Henry Meyer 1907 Yanzhou, Shandong Sheng, China
Ailanthus altissima photographed in Yanzhou, Shandong Shen, China by Arboretum plant explorer Frank Henry Meyer in 1907. Courtesy of the Arnold Arboretum Horticultural Library and Archives. Frank Henry Meyer

The fortunes of Ailanthus-based sericulture quickly turned perilous, however. In 1867, the Transactions reported that “the season had been very unfavourable” for Dr. Wallace; “long continued rain and wind made great havoc, and a severe hail-storm which happened early in August riddled the Ailanthus leaves, and knocked down the worms, of which many were killed. Ailanthiculture was precarious elsewhere, too: “Mr. S. Stevens had recently visited Lady Dorothy Nevill’s Ailanthery, where also many larvae had been blown off the trees by the wind, and it was necessary to employ a man or boy to replace them on the leaves…. “Prof. Westwood said that wasps carried off the newly-hatched larva…. a correspondent of his had had a few of the larvae in-doors, but two of them escaped; after a time two specimens of the perfect moth were found upon the single Ailanthus tree which was growing in the garden.” 

Ailanthiculture quickly faded, along with other Victorian fads like rubber corsets and vinegar drinking. This folly had a dark side: for all their quixotic industry, enthusiasts sought to appropriate Ailanthus and its silk moth, to introduce “improvements,” to extend the imperium of science and commerce. The Ailanthus silk moth escaped its containment and went feral; the tree of heaven flourishes, too, outside the bounds of ailanthery and arboretum alike. In growing 695-80*B from a feral tree, Del Tredici did more than propagate a striking specimen; he also ensured our collections document and address these legacies.