Butterflies have long been admired and collected by humankind, and modern enthusiasm for the colourful lepidopterans hasn't waned. Gliding under the radar of CITES regulation, butterflies are easily traded online and shipped internationally as dried samples, difficult to detect by customs as they do not show up on x-rays.
To quantify the extent of online butterfly trade, this study monitored eBay transactions for a year, logging more than 50,000 sales of 3,767 different species, representing nearly 20 per cent of all butterflies on Earth. The authors collated a database of all traded species with potential sales predictors, including distribution, abundance, conservation status, traits and phylogenetic distinctiveness.
As aesthetic appreciation by consumers is difficult to quantify, the authors implemented a rating system based on GBIF-mediated occurrence images of pinned, male specimens. They asked crowd-sourced judges to iteratively pick their favourite between two specimens, continuing for 100 randomized pairs per judge, until reaching a stabilized ranking after 200 judges.
Often shipped from the Global South to the US or Europe, specimens' median price was $6.75. Sale prices amounted to about a third of the average daily wage in the countries of origin. At the extreme end, a single pair of Ludlow's Bhutan swallowtails (Bhutanitis ludlowi) (EN) sold in Russia for just under $9,000.
Further analysis revealed that while species perceived as "rare" (e.g. threatened according to IUCN or regulated by CITES) had higher prices, the crowd-sourced aesthetic ranking best predicted a species' trade volume. Features such as wingspan, shape and colour explained about half of the variance in aesthetic ranking. The highest ranked species were most often large with brilliant colours, such as Morpho menelaus and Papilio ulysses.