The Mystery
of the Wet Lizards
Why do they stand like that . . . and in the rain?
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A Texas horned lizard standing in its rain-drinking posture. This magnified view shows a channel between two scales. Water in the channel will stick to the sides and move along the channel. |
One rainy afternoon in Arizona, Wade Sherbrooke saw a strange sight. Outside, in a wire cage, his two Texas horned lizards were standing in an unusual way.
“Both lizards stood with their legs extended and spread far apart,” he says. “Their backs arched up, and their tails and heads pointed down. They were slowly and rhythmically opening and closing their jaws, ever so slightly.”
He thought the lizards might be drinking rainwater that collected on their wide backs and flowed to their mouths. He got this idea from reading about another lizard, the Australian thorny devil.
The thorny devil can be placed in a bowl with only its underside touching a shallow pool of water in the bottom. Then water creeps up the lizard’s skin and across its surface. (See “How Water Flows Up” below.) When the water reaches the head, the lizard opens and closes its jaws as it drinks. Scientists thought that thorny devils drank this way during rainstorms, but no one had seen them do it.
“Did I just see horned lizards drinking in a similar way?” Wade wondered. He set out to answer that question.
Experiments with Lizards
First, he wet his lizards with a lawn sprinkler. He recalls, “My lizards
watched me, and never took up the body stance or moved their jaws.
They seemed too concerned to move, probably considering me a predator.”
Next, Wade dripped harmless colored water from a syringe onto the lizards’ backs. “The dark blue water spread through the channels between their scales to form a lace-like pattern,” he says. “As the water moved outward and up to cover each lizard’s head, the lizards began opening and closing their mouths, swallowing the water.”
Off to Australia
Did the Australian thorny devil drink in a similar way? No one had reported
seeing a thorny devil drinking, except in a bowl. Wade wondered how
they drank in their desert habitat. He traveled to Australia to try to
find thorny devils and rain at the same time. Amazingly, in nine weeks,
he found both three times.
“An Australian biologist and I drove to a remote location in the southwestern part of the continent,” he recalls. “We soon located ten thorny devils. To find them again after release, we taped a thread bobbin to their tails and tied the free end to a shrub. As the lizards walked away, they left a thread trail.”
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An Australian thorny devil with a thread bobbin attached to its tail. |
The scientists checked up on the lizards daily. When rain fell, Wade stooped and crawled through vegetation, following thread trails. His reward was the sight of thorny devils standing in the rain. None of these lizards had the rain-harvesting posture that Wade had observed in horned lizards. But they did open and close their mouths slightly to drink.
After a light rain, Wade found each thorny devil again. Next to some of the lizards, he saw smooth, circular areas of sand where the lizards had rubbed their bellies.
“What a surprise!” he says. “By rubbing their bellies in the damp sand, they used the channels between their scales to pull water from the sand onto their skin.”
Were Horned Lizards Drinking?
Back in the United States, Wade tested to see if horned lizards really
were drinking the rainwater that flowed across their backs.
He built an experimental box for releasing drops of water onto the reptiles. He weighed the lizards before and after dripping water on them. The amount of weight they gained depended on how fast the drops fell and the number of times they opened and closed their jaws. This result showed that the animals really were drinking.
Observing two horned lizards in his yard led Wade Sherbrooke to discover how some lizards harvest water from rare desert rainfall. Proving his idea took years and helped him earn a doctoral degree in the science of reptiles (such as lizards) and amphibians (such as frogs and salamanders).
He says, “When I see a horned lizard standing in the rain, I’m now convinced that it uses its back and scales to harvest water. I hope you are, too.”
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