Quirks & Quarks

Australian monitor lizards build underground condos used by dozens of other species

Complex and deep helical burrows host lizard eggs and many other species

Complex and deep helical burrows host lizard eggs and many other species

Ecologist Sean Doody excavates a burrow where a monitor lizard has laid eggs (Submitted by Sean Doody)

Originally published on January 30, 2021.

While excavating burrows of the yellow spotted monitor lizard in Australia, researchers were surprised to find dozens of species and hundreds of individuals amphibian and reptile, as well as lots of insect life. They had no idea that the lizard burrows were such important habitats for a wide range of other species.

Australia's yellow spotted monitor lizard is a top predator that eats just about anything — to its cost. Because they don't know not to eat the invasive, poisonous cane toad, their numbers are crashing. This could have serious implications for many other species as well, thanks to this new finding.

Sean Doody, an ecologist from the University of South Florida and colleagues in Australia began to study the impact the invasive cane toad was having on these lizards, by investigating their burrows. 

The yellow spotted monitor lizard of Australia (Submitted by Sean Doody)

Ecosystem engineers

In a new study, the scientists describe that the monitor lizards are ecosystem engineers. They dig large, intricate burrows — or warrens — for the purpose of laying their eggs. The spiral-shaped burrows go about four metres deep. The lizards lay their eggs at the bottom and leave. 

Illustration of a monitor lizard burrow (Submitted by Sean Doody)

When the burrows were excavated for the study, Doody and his colleague were surprised to find many other creatures had moved in. In total they found 750 individual animals of 28 different species in 16 separate burrows. There were 418 frogs in one burrow alone.

Arthropods, snakes, toads and other lizards had moved in for a variety of purposes. Some use the burrows to hide from predators or the heat, others feed on prey they catch in them, some hibernate in them, and some even use them to lay their own eggs.

The spiral tunnel of a monitor lizard burrow (painted to highlight the spirals) (Submitted by Sean Doody)

The cane toad issue

With so many monitor lizards dying from eating cane toads, there will be a cascading impact on many other species. Doody and his colleagues hope to investigate this question further in future work.