Frog and Toad Bladders Hunt and Remove Foreign Objects

Zoologists implanted frogs with radio transmitters. The result was that most of the transmitters were found in the frogs’ bladders or fully excreted. Further experimentation indicated that certain species of frogs and toads have bladders that can detect, surround, and excrete foreign objects.

At Wired, Dave Mosher writes:

They enlisted five green tree frogs and five cane toads, implanting small inert beads in each the same way they implanted the radio transmitters. Each tree frog expelled its bead within 23 days. One cane toad also gave its bead the boot, and the beads in the other four toads had migrated to their bladders.
To unravel the secrets of the process, the zoologists implanted beads in 31 more cane toads, toxic amphibians native to South America but introduced to northeastern Australia in 1935 to control beetle infestations. (Since then, Shine says, the toads have become invasive and poisoned populations of large predators such as pythons. As a result, ecologists now closely track their numbers and behavior.)
Toads dissected on sequential days revealed that the bladder grew a thin offshoot of cells to surround the bead, which later developed into mature, bladder-like tissue and merged with the organ’s main cavity. From there, they “floated freely in the urine” and were peed out if near the bladder’s opening.

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