If a giant grizzly bear was to pop out from behind a bush and start approaching you, your first reaction would probably be to run immediately for your life in the hopes of reaching safety as quickly as possible. However, when a black-spotted pond frog sees an approaching predator, it actually waits for the attacker to move nearer before trying to flee. Why do some prey allow their predators to get closer, instead of getting the heck out of there? After all, the more distance between prey and a predator, the better for the prey, right? Not necessarily, according to recent research by Nozomi Nishiumi and Akira Mori. The two scientists from Kyoto University, Japan, studied the interactions between a predator (the Japanese striped snake) and its prey (black-spotted pond frog) to figure out what determines the victor in standoffs between the two.

Nishiumi and Mori went out into rice fields to watch snakes and frogs interact in the wild. In each of the encounters they saw, the frogs safely evaded the snakes. These snakes are known to regularly gobble up frogs, so there must have been a reason why these frogs kept gaining the upperhand. Nishiumi and Mori then brought some of the snakes and frogs into the lab, so that they could change the distance between the predator and its prey. They did this by putting the frogs on little leashes, which they used to nudge the animals in the ‘right’ direction. Once the snake and frog had noticed each other and were a certain distance apart, the scientists released the leash, allowing the snake and frog to duel unencumbered.

The researchers found that below a critical distance (which can be just 5 cm), whoever made the first move had the advantage. Beyond that distance, making the first move meant you were more likely to fail. In the snakes’ case, that meant missing a meal, but in the frogs’ case, that meant filling the snake's belly.

Below the critical distance, snakes can get the jump on frogs before they have a chance to react and frogs could hop out of danger before snakes could react, so the early bird gets the worm in these cases. However, jumping too early beyond the critical distance is risky for the frog for two reasons. The first is that if the frog moves first, it risks giving away its position to a snake that has not seen it yet. The second being that frogs cannot change direction midair, making them sitting (or jumping) ducks for a snake that can easily intercept them. On the other hand, if a snake strikes too early, it is also unable to change its direction mid-strike, so the frog is able to dodge the initial assault and escape before the snake has a chance to reload for the next attack.

People and perhaps other animals use this strategy too. Whether it is fencing, boxing or dueling, if you wait for your opponent to make the first move, you can gain the upper hand by reacting to the information they give you, informing your response. Like gunslingers in a wild west standoff, snakes and frogs wait motionless for their enemy to make the disadvantageous initial move. If this strategy did not work, our spaghetti western movies would be a lot less suspenseful…and much shorter.

A game of patience between predator and prey: waiting for opponent's action determines successful capture or escape
Can. J. Zool.