Devil Holes: Yellow Spotted Lizards Dig the Deepest Nests

Deep in the earth of Australia and Southern New Guinea there are strange spiral-shaped holes that seem to just go and go. These holes, called "devil's corkscrews" are actually the burrows of the yellow spotted lizard. Now researchers have determined that these misunderstood reptiles are actually the deepest digging vertebrates in the known world, even if the function of their holes' unique shape remains a mystery.

According to a study recently published in the Biological Journal of the Linnean Society, the discovery of these incredibly deep 'helical burrows' (up to 12 ft deep)  was actually relatively recent, and shows that the monitor lizard Varanus panoptes, commonly known as the yellow spotted lizard, handily out-digs any other known reptile.

It's important to note that despite its name, a tendency to dig deep, and even infamously aggressive behavior, this is not the monstrous yellow spotted lizard featured in the popular novel and movie "Holes." That deadly and onion-fearing lizard is unsurprisingly fictional. However, it's very likely that the genuine article, which reportedly has a very painful bite of its own, was a source of inspiration for author Louis Sachar.

So if these aren't the devilish lizards from lore, why the 'devil's corkscrews?' According to Sean Doody, a researcher with the University of Newcastle who discovered the burrows and coauthored the study, the lizards use the depth of their burrow to protect their young. (Scroll to read on...)

"Our data show that the most likely explanation for the deep nesting is to prevent the eggs desiccating over the long dry-season incubation (~8 months)," Doody recently explained in the popular Zoologger blog.

"Alternatively, the lizards may avoid shallower nesting because even slight daily temperature fluctuations are detrimental to developing embryos," he wrote in the study. "Our data show that this species may have the most stable incubation environment of any reptile and possibly any ectotherm."

What's interesting is that this does not explain for the corkscrew design of the burrow. It had been thought that the structure may in some way maintain more constant temperature, thanks to limited air-flow. However, Doody and his colleagues quickly found that this wasn't the case.

Another theory is that the corkscrew deign helps keep predators out, as many will not have a body suitable for twisting and turning through the tunnel.

Regardless of the reason, the researcher say they haven't seen devil's corkscrews since the discovery of the fossilized burrows of extinct beaver-like animals called Palaeocastor that lived more than 20 million years ago. To see this adaptation taken up once again, and by a modern reptile, they write, is nothing short of "extraordinary."

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