The movement of cricket frogs across water has often been likened to the act of walking on water, but recent research reveals a different perspective.
Can frogs realmente walk on water?
Various species have captured the imagination of many with their remarkable ability to hop sideways and leap off the surface of ponds as if it were solid ground. One such species found in Virginia and North Carolina is the cricket frog. The locomotion of these frogs could offer valuable insights for advancements in robotics, aquatic vehicles, and more.
Jake Socha, the Samuel Herrick Professor of Mechanical Engineering, is at the helm of a research group that investigates the cricket frog’s unique “skittering” ability, which describes their pattern of jumping repeatedly. The research team’s findings were detailed in the Journal of Experimental Biology, with graduate researcher Talia Weiss as the lead author.
“Skittering isn’t a well-defined term for this behavior — one naturalist coined it to describe frogs ‘jumping on water’ back in 1949, and since then, it has been used in this context throughout literature,” Weiss explained. “Part of our work involves not only analyzing this behavior in cricket frogs but also refining the scientific definition of ‘skittering.’
How do they accomplish this? In their research, Socha’s team discovered that although many believe these frogs can traverse water without sinking, achieving this feat may necessitate very specific anatomical features. What unique traits do cricket frogs possess compared to others?
“Our lab has investigated a variety of animals, with many demonstrating intriguing ways of moving through their environments,” Socha remarked. “The familiar cricket frog is right in our backyard, yet it surprised us with its remarkable abilities, further fueling our desire to explore the natural world.
High-speed footage for rapid frogs
Cricket frogs rank among the tiniest frogs in North America, easily fitting on an adult’s thumb. To capture their movements, the team utilized high-speed photography. They documented how the frogs jump both on solid ground and in water, closely observing their leg movements in both environments.
The findings indicated that the frogs do indeed sink with each jump. While the term “skittering” suggests that they leap freely with only their feet touching the water, the footage revealed a different story. Socha, Weiss, and colleagues discovered that upon landing from a jump, the frog’s entire body would submerge. Their actions resembled a series of sudden plops rather than an elegant dance on the water. A more fitting description of their movement might be “porpoising,” akin to how porpoises or dolphins leap from beneath the water surface.
Launching from below
The illusion of the cricket frog gracefully hopping across water is largely due to their swift motion.
To document this exceptionally quick behavior, the team set up a 20-gallon glass tank and released the frogs inside. High-speed cameras, capturing up to 500 frames per second, were positioned at the side of the tank to film the action both above and beneath the water. As the frogs jumped, the team documented their escape.
The resulting footage was slowed down significantly. Upon review, the researchers were surprised to observe that the frogs did sink.
“It’s intriguing how easily we can be misled by the rapid movements of animals,” noted Socha. “In this case, we were tricked by a frog that seems to skip across the surface but actually performs a series of jumps and dips in rapid succession. While frogs are known for their jumping prowess, few exhibit this porpoising behavior, and the reason remains unclear. Is it a unique aspect of their jumping technique or simply related to their small size?”
Through slow-motion analysis, team members studied how the frog retracted and extended its limbs. They also found that the angle at which the frog’s body met the water impacted its ability to maintain balance. The researchers categorized each jump cycle into:
- Takeoff, initiated from a submerged position
- Aerial phase, the duration spent in the air after a jump
- Re-entry, the return to contact with the water
- Recovery, the reset for the next jump
In a bit over one second, a frog would launch itself from being fully submerged, extending its feet to propel its body above the water’s surface. While airborne, its hind legs remained stretched out, and its front legs transitioned from being tucked against its body to reaching forward. The front legs made contact with the water first during re-entry, while the rear legs were still extended as it began to sink. As it submerged, the back legs bent back into a jumping position to initiate the next leap.
This action closely resembles a belly flop.
The team recorded instances where the frogs executed up to eight consecutive jumps, each completed in under a second.
Unraveling the mystery of skittering is a significant breakthrough in biological science, but it also suggests new possibilities. This insight could inform the design of bio-inspired robotics, such as rapidly deployable water testing systems or amphibious drones for measuring water depth. These futuristic innovations can take inspiration from proven natural methods that frogs have used for ages.
