Mertens’ Water Monitor

Keeled scales on the tail of a mertens’ water monitor

Except for the frillies, this encounter has probably been my most emotional one so far. I had been waiting to meet a goanna for a long time, only seeing a glimpse of a lace monitor (Varanus varius) in Sydney and a spotted tree monitor (Varanus scalaris) my first day in the savannah woodlands. The monsoon rains flooded parts of the Arnhem highway in the Top End rendering it inaccessible at times, but reptiles and mammals are on the move. I spotted this water monitor on the road and initially assumed it was a roadkill. As I approached the giant lizard I was shocked to see it was completely intact and even more shocked to see its eye staring blankly at me. Immediately my heart rate skyrocketed — finally a varanid!

Photographed after disturbance [4] unless otherwise stated

Photographed in situ [1]

In all my days and nights of road cruising for reptiles I had never seen a goanna, partially due to population declines since the arrival of cane toads. It’s more common to see them crossing the road at dusk or dawn, so I hadn’t really considered finding one at 2am. This goanna, about a meter in length, found a comfortable spot on the road adjacent to the floodplains. Since mertens’ water monitor is an aquatic species, it is exquisitely adapted for swimming and moving around waterways. The tail is about 1.5x the length of the body with a high ridge to propel the giant lizard through water. I was impressed at how maneuverable the tail was, wrapping around my arm several times, twisting and turning like a being of its own. The nostrils are positioned dorsally so that the goanna can breathe while swimming on the water’s surface, and like all monitors, they have a long forked tongue and an acute sense of smell to locate fish, frogs, invertebrates, carrion, and even crocodile and turtle eggs.


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