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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Destination Tambopata River, Peru: The search for salt by birds and birdwing moths, Urania sp.


Soil on the bank of the Tambopata River supplies vital nutrients to a Urania moth.


Bug of the Week continues its adventures in tropical places with a stop on Tambopata River, tributary of the mighty Amazon. Riverbanks along the Tambopata are famous for their clay licks. Clay licks are assembly points where dozens of species of birds gather by the hundreds and consume beakfuls of clay soil on the exposed riverbanks. Why in the world do these plant eaters gobble soil? Two hypotheses may help to explain. One idea has it that some of the vegetation and fruit eaten by macaws and parrots are laced with toxins. Clay consumed by the birds may bind these toxins and help prevent them from being absorbed by the digestive tract, thereby preventing damage to tissue and organs. These bound toxins are passed out of a bird’s body with the clay. A second school of thought has it that some essential minerals, especially sodium, are in short supply in the Amazon basin. The greater the distance from a salty ocean the less salt-laden is rainfall. In addition, scientists believe that prodigious tropical rains may leach salt from the soil. To obtain vital sodium many birds and mammals search for salt laden soils, so called salt licks. Clay licks along Peru’s Tambopata are thought to be places rich in salt.


Amidst a cacophony of excited screeches and squawks, several species of parrots flock in droves to clay licks along riverbanks in the western Amazonian basin.

Ah, but dazzling birds are not the only ones who need sodium in their diet, insects do as well. Hundreds of butterflies and moths congregate on muddy flats and puddles to lap nutrient-laden fluids from the riverbank. Among the most spectacularly stunning of these insects are birdwing moths in the genus Urania. At first look these beauties appear to be butterflies, but in fact these moths belong to the same clan as inchworms found in Maryland. In addition to their stunning beauty, some species of Urania moths are famous for their long distance migrations, similar to those seen in North American monarch butterflies. Much mystery still surrounds migrations of these gorgeous fliers. One hypothesis has it that a decline in the quality of patches of the host plant, vines in the genus Omphalea, may trigger massive emigration of moths from one part of the range to another. It appears that birds and birdwing moths unite in their quest for salt along the banks of the Amazon’s tributaries in eastern Peru.   


Spectacular birdwing moths assemble on the muddy Tambopata riverbank to imbibe nutrients from the soil.


“On the biogeography of salt limitation: A study of ant communities” by Michael Kasparia, Stephen P. Yanoviakc, and Robert Dudley, and “Host Plant Toxicity and Migration in the Dayflying Moth Urania” by Neal G. Smith, were used as references for this episode. Inspiration for this episode came in part from the guides at Posada Amazonas along the Tambopata.