National Geographic

Meet The Predator That Becomes Blind When It Runs After Prey

The tiger beetle can run so fast that it blinds itself.

There are 2,600 species of these long-legged predatory insects, and the fastest can sprint at up to 5 miles per hour, covering 120 of its body lengths in a single second. For comparison, Usain Bolt covers just 5 body lengths per second. To match the beetle, he’d have to run at 480 miles per hour.

Tiger beetles use this incredible speed to run down both prey and mates. But as they sprint, their environment becomes a blur because their eyes simply can’t gather enough light to form an image. They have extremely sharp vision for insects, but when they’re running, the world smears into a featureless smudge. To compensate, the beetle has to stop to spot its prey again, before resuming the chase.

It seems like a bad evolutionary joke: a hunter that loses sight of its prey whenever it runs.

But tiger beetles don’t mind because… well… they are really, really fast. They can afford to stop in the middle of a chase because they are so ridiculously quick when they’re in motion. It’s like the aforementioned Bolt pausing at the 50-metre mark for a drink, and still winning.

Hairy-necked tiger beetle. Credit: Daniel Zurek.

Hairy-necked tiger beetle. Credit: Daniel Zurek.

Cole Gilbert at Cornell University discovered the tiger beetles’ staccato hunting style in 1998. Now, together with Daniel Zurek, he has worked out how they cope with another problem: obstacles.

At high speed, it’s hard enough to avoid incoming obstacles. But try doing it when your eyes can’t make out anything, much less small pebbles or sticks. A running tiger beetle is permanently in “collision mode”, says Zurek. “It’s like when I’m driving a car really fast and not wearing my glasses. When something hops in the road, I can’t stop in time.”

He discovered how they cope by watching an American species—the hairy-necked tiger beetle, Cicindela hirticollis. When it runs, it always keeps its antennae in the same fixed position: straight ahead, angled at a V, and held slightly above the ground. The antennae can move, but they never do while the beetle’s in motion.

The antennae are obstacle-detectors. If they hit an obstacle, their flexible tips bend back before springing forwards again. The beetle moves too fast to change course, but it can tip its body slightly upwards so that it skitters over the obstacle rather than running headlong into it. It’s like a blind person holding two white canes (and wearing rocket skates).

“Because of their shape, the antennae can slip over the edge of an obstacle, which tells the beetles that there’s a top they can run over,” says Zurek. He saw how effective this is by filming tiger beetles running down a long track with a piece of wood in the middle. If their antennae were intact, they cleared the obstacle most of the time, even when Zurek painted over their eyes. But if he cut the antennae off, the beetles frequently face-planted into the wood.

This solution is not only effective, but cheap. The beetles could potentially deal with motion blur by evolving more sensitive eyes, but it takes a huge amount of energy to pay for an eye with good temporal resolution. They would also have to analyse that information, and their small brains probably don’t have the processing power. Fortunately, they don’t need anything that over-engineered.  Their antennae provide them with all the collision-detection they need.

Zurek thinks that human engineers should take note. One of the first autonomous robots—Shakey—found its way around with some “bump detectors”. If they hit an obstacle, they bent, and Shakey would back up.

But modern robots rely on cameras. NASA’s Curiosity rover, for example, is currently trundling over Mars with the help of eight hazard avoidance cameras, or Hazcams. “As humans, we tend to think first and foremost from a visual standpoint,” he says. “Many really sophisticated robots rely on an array of cameras that analyse on the fly, which is very computationally intensive.” The tiger beetle’s solution would be simpler, and might help robots to move much faster than Curiosity’s leisurely pace.

PS: How does one catch an insect that moves so quickly? With great difficulty at first, but Zurek says, “It’s pretty fun once you get the hang of it,” he says. “You have to fool them by coming up behind them really slowly and then lowering yourself. I get them around 60 percent of the time.”

Reference: Zurek & Gilbert. 2014. Static antennae act as locomotory guides that compensate for visual motion blur in a diurnal, keen-eyed predator. Proceedings of the Royal Society B http://dx.doi.org/10.1098/rspb.2013.3072

There are 10 Comments. Add Yours.

  1. Mike Lewinski
    February 4, 2014

    So speaking of mates, I encountered pairs of Western Red-Bellied Tiger Beetles down on the Rio Grande last summer. They were stacked up and running around on the rocks like this:

    http://flic.kr/p/fnBV6Q

    Periodically a single interloper would come upon a pair and run up to them, but they’d run it off as a team. I really have no idea what was actually going on. Attempted threesome? Trying to steal a mate? I’ve got video and will dig it out if anyone’s interested in helping me shed some light on the behavior.

    Tiger beetles are awesome. The information in this blog makes them awesomer. Thanks Ed!

  2. Mike Lewinski
    February 4, 2014

    I forgot to subscribe to comments on my first post. I also dug up a bit of the video I’d posted of those mating? tiger beetles:

    https://www.facebook.com/photo.php?v=10151754599727173

  3. Gandhar Joshi
    February 6, 2014

    Nature is awesome.

  4. W. Benson
    February 6, 2014

    Mike, you may have a case of mate-guarding. In insects females often mate several times, and the sperm from the last mating male often fertilizes the great majority of a female’s eggs. A male can sometimes guarantee his reproductive success by preventing other males from mating later with the same female. Holding onto to the female (assuming that it is indeed a male gripping a female in your video) might prevent the female tiger beetle being mated again and guarantee the paternity (together with the genes for the behavior) of the guarding male.

  5. RainerM
    February 6, 2014

    But many flying insects like dragonflies or brachyceran diptera move even faster while apparently not impeded in their visual abilities. What’s so special with tiger beetles’ eyes?

  6. Chris
    February 6, 2014

    The tiger beetle in the first photo looks more like the oblique-lined tiger beetle (C. tranquebarica), not the hairy-necked (C. hirticollis).

  7. METIN GUNDUZ
    February 7, 2014

    Evolutionary vise “ the assumption that the visual information –data- is vital ” for every species , simply because the environment of each species is different , and the “ACCURACY” of sensation(data) is more important for survival and evolution of that species … Chemo , mechanic , thermo sensation of antennas in other words “the multiple function” , compared to limited “vision” and information they get from their eyes , visual they can NOT be sure % 100 what they are seeing , BUT they can be sure close to % 100 with 1-Chemical 2-Temperature 3- Mechanical 4- as well as two antennas movement called “Spatial” 3 dimensional information ALL FOUR SENSATIONS COMBINED- THE ADDITIVE INFORMATION they can get from their antennas , in addition they MAY ? theoretically get the 5th sensation from their antennas which is “The Electrostatic Surface Sensation” long before even touching the surface of the object they are fast approaching straight” . So the bottom line is “The antennas gives more vital and accurate(reliable) and faster information “ for survival ` evolutionary vise than the “visual” that they CAN NOT be sure % 100 , in other words visual can be “confusing” and not as accurate as the potential 5 sensations combined they can get from their antennas . Olfactory receptors located on the antennae bind to free-floating molecules, such as water vapor , and odors including pheromones. The neurons that possess these receptors signal this binding by sending action potentials down their axons to the antennal lobe in their brain . Visuals can be illusions and can not be relied on for survival …But chemical/temp/mechanical/spatial data/electrostatic data ALL COMBINED from the antennas are IRREPLACEABLE and PRICELESS ..

  8. lkr
    February 8, 2014

    Sorry, Metin — tiger beetles undoubtedly are able to use chemical cues with their antennae, but in the hunting behavior described here they are just tactile –“cat’s whiskers” — to avoid obstacles when they are in blur mode.

    • METIN GUNDUZ
      February 9, 2014

      In order to be so sure for that you got to be a `tiger beetle` …! Joke aside the statement that the Tiger Beetle uses only` mechanical` sensations from its antenna when it is on a `hunting mode` ; is just an `assumption` and a `wild guess` and it might well be `wrong` as it happens frequently for `the assumptions` over and over again in Science as we well know .
      The chemical/ thermal/ `spatial 3 dimensional data obtained by simultaneous and dynamic use of 2 antennas ` and even presumed existence of – non tactile- Electrostatic data that I had mentioned earlier from the Antenna of Tiger Beetle might well be `in constant play` `at all times` when it is on `hunting mode` upon approaching the prey . Simply because : There is no `evolutionary` or logical reason whatsoever that the Tiger Beetle will voluntarily `withhold to use ` its `existent and ever ready other sensory weapons from its antenna ` in addition to the `mechanical sensation` in a`hunting mode` ..
      Of course currently it is not technically possible to measure the `action potentials down their axons to the antennal lobe in their brain coming from different sensory receptors already exists on their antennas ` when it becomes technically available in the future , then I can foresee now that they will be able to measure that too . But for now “the evolutionary logic” predicts their usage at all times for the “optimum” results durıng hunting mode …

  9. METIN GUNDUZ
    February 9, 2014

    By the way “Cat whiskers” is not good `analogy` here because the shaft of whisker consists of inert material called `keratin` and the whisker shaft contains `no nerves`or receptors whatsoever in other words the whiskers does not carry `Chemical\Thermal` receptors as we well know , only the follicle of whiskers they originate from has `mechanical sensors` at the root end , BUT the `insect ` antenna does carry different receptors all along it`s shaft as well as nerves inside the antennas . Comparing whiskers with antenna of insect is like comparing apples with oranges …

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