Sloth moths were first discovered and collected by August Busck in 1907 during the Smithsonian Biological Survey of the Panama Canal Zone. He was a Curator of Lepidoptera (moths & butterflies) at the National Museum of Natural History (NMNH). In 1908, Harrison G. Dyar, also a Lepidoptera Curator who worked on Pyraloidea or snout moths, described this new species as Cryptoses cholepi (Dyar 1908). He said Busck had “observed a large sloth…fall from a palm tree….When the animal fell, a number of small moths were dislodged by the shock and flew out of its fur.”
At that time, Dyar hypothesized that the caterpillars also lived in the fur, but Waage & Montgomery (1976) discovered that the caterpillars of C. cholepi actually lived in and fed on the dung of the three-toed sloth on Barro Colorado Island, Panama (Smithsonian Tropical Research Institute). He observed: “Sloths descend from the forest canopy to its floor at about weekly intervals to defecate, where, hanging to a vine by their forelegs, they dig a depression with their hind claws, deposit about a cupful of these pellets, then cover the dung loosely with leaf litter.” The female moth with fertilized eggs then leaves the sloth and lays the eggs in the dung.
Waage & Montgomery (1976) hypothesized that the moths benefitted from the sloth’s behavior by providing a safe location for laying eggs away from bird predators and perhaps even enhancing the moth’s diet with sloth secretions. They described the relationship between the moth and the sloth as “phoretic”— the sloth transports the moths down the tree.
As curator of the sloth moth collection in the NMNH, I have created the largest sloth moth collection of Cryptoses cholepi in the world. When I collect at night with lights in the Neotropics, I find sloth moths primarily appear in mature forests. Although I do not see them, I know there are sloths in the vicinity. Currently, there are 4 other known species of sloth moths in the New World tropics, presumably associated with other species of sloths. Bradley (1982) described two new species of sloth moths associated with sloths in Brazil.
Sloth moths are very unique in the subfamily Chrysauginae, a group of about 400 brightly colored species of moths, whose caterpillars are primarily plant feeders. One could never guess that sloth moths are a member of this subfamily. Unlike their brightly colored relatives, sloth moths are brown to camouflage themselves in the fur of the sloth (see photos). In addition, they differ from their relatives in their structural modifications. Many other chrysaugine males have wings designed to produce sound to attract females and elaborate reproductive structures for mating; sloth moth wings and reproductive organs are lacking many of these typical structures. The males presumably lost these intricate structures for finding and mating with females as the tight relationship with sloths evolved.
Recently, I dissected and identified samples as Cryptoses cholepi for a study by Pauli et al. (2014). The sloth’s behavior of descending a tree to defecate is energetically costly. This risky behavior is the leading cause of mortality for sloths. But, Pauli and coauthors hypothesize that this symbiotic behavior augments the sloth’s limited diet. They found that the sloths with more moths had more inorganic nitrogen to fuel algal growth, which means more food for the sloth!
Bradley, J.D. 1982. Two new species of moths associated with the three-toed sloth in South America. Acta Amazonica. 12:649-656
Dyar, H.G. 1908. A pyralid inhabiting the fur of the living sloth. Proceedings of the Entomological Society of Washington. 9: 142-143
Pauli, J.N., J.E Mendoza, S.A. Steffan, C.C. Carey, P.J. Weimer and M.Z. Peery. 2014. A syndrome of mutualism reinforces the lifestyle of a sloth. Proceedings of the Royal Society B. 281: http://dx.doi.org/10.1098/rspb.2013.3006.
Waage, J.K. and G.G. Montgomery. 1976. Cryptoses choloepi: a coprophagous mtoh that lives on a sloth. Science. 193: 157-158
Dr. M. Alma Solis, Research Entomologist, Systematic Entomology Laboratory, ARS, USDA Curator of Lepidoptera, National Musuem of Natural History, SI
[Disclaimer: Content and opinions expressed on this blog do not necessarily reflect the views of nor are they endorsed by the National Museum of Natural History or the Smithsonian Institution]