The sad story of Urania sloanus

This is the story of what used to be one of the most beautiful moths in the entire world: Urania sloanus (Sloane’s urania).  It was endemic to the lowland rainforest habitats of Jamaica. Sloan’s urania was considered to be one of the most spectaculair species of Uraniidae moths; however, around the year 1900 it went extinct and has never been recorded since.

Urania sloanus, photographed in Naturalis Biodiversity Centre. Photographer: Bart Coppens 

So what happened?
The remains of the now-extinct moth still haunt antique collections and serve as a bitter reminder of the importance of preserving wildlife. It is unknown how many specimens of the moths have been collected before they went extinct, but nowadays they are scarce: a single specimen may have a market value of  10.000 up to 25.000 dollar(!).

Urania sloanus was a highly iridescent day-flying moth – it’s iridescent colours, while looking attractive to humans, also had a more important function: they were a warning to potential predators, signalling the fact that the moth is in fact toxic.

In 1880 and 1881, the English naturalist Philip Henry Gosse wrote two reports for the entomological journal The Entomologist called Urania sloanus at home and Urania sloanus at home II.  In Jamaice imagoes of Urania sloanus could be found in great abudance mainly between April and June, which supposedly was their peak season. The adults could be seen feeding on flowers in great numbers, often swarming avocado flowers.  The dayflying moths became active at sunrise, only to settle down again until afternoon, thus avoiding the hottest time of the day. It was found in the Blue Mountains and lowland rainforest habitats.

Interestingly, the moth is presumed to be extinct, despite the fact that there still is a significant amount of primary rainforest in Jamaica today.  (David C. Lees & Neal G. Smith 1991) They however conclude: “Although habitat loss in Jamaica may have been a factor in its demise, substantial tracts of primary forest still remain. The reported
foodplant of U. sloanus on the North coast at Ocho Rios, Omphalea
triandra L. (Gosse 1881: see Table 3) apparently is still widespread in
wet forest on limestone in the island (Adams 1972). However, it is likely
that that moth also feeds on O. diandra, reported, although not recently,
from Portland County (Adams 1972, Hemsley 1885), a former locality
for the moth (Townsend 1893). Periodic swarms of moths at flowering
trees in the Blue Mountains of Portland were intervened by years of
great scarcity (Townsend 1893). The population of U. sloanus apparently
crashed below a sustainable level, perhaps a victim of loss of one
of its larval food plants. ” – FOOD PLANT ASSOCIATIONS OF THE URANIINAE

Uraniidae moths all over the world have complicated, migratory relationships with their respective food plants.  The following report I found in the report also solves a piece of the puzzle:From  Smith, Neal G. 1983. Host plant toxicity and migration in the dayflying moth Urania. Florida Entomologist 66(1):76-85.

In this report it is concluded that Urania species simply need to migrate. This is because their food plants are slow growing, tropical vines in the genus Omphalea. Interestingly, when the caterpillars of Urania feed on these food plants, the host plants slowly start to release more toxins. These toxins lower the survival rates of the caterpillars and allow the plants to “fight back” against their main herbivore enemy, Urania moths. Over the course of several years, food plants in habitats in Urania moths will become unsuitable for larval consumption. This explains why day-flying Urania moths can be over-abundant in some areas for months or years and then suddenly seem to vanish. They are forced to live a continuously nomadic lifestyle, dissapearing from and revisiting habitats made unsuitable or suitable due to larval infestations. It is thought that host plant toxicity and migration cycles are interconnected. In fact, there is evidence that a high concentration of toxins in the  food plant leaves consumed by caterpillars  results in migratory adults, while a low concentration of toxins results in “residental” non-migrating adults. The population dynamics and fluctuations of day flying Uraniidae moths are heavily regulated by the capabilities of their food plants to “fight back” and produce toxins in response to larval grazing; nomadic adults simply seek out ungrazed, and thus less toxic plants.

This is why Urania sloanus is presumed to be extinct, despite the fact that many of its primary rainforest habitat is still intact. The deforestation of the lowland rainforests, that were turned into agricultural zones instead, may have been of great importance to the migratory cycle of Urania sloanus, forming a potential “basin” of viable, ungrazed host plant that were utilised by emigrating adults from other populations.

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