The King of Beasts, the lion, kills 25% of the prey it seeks to attack, according to a recent article by Natalie Angier in the science section of the The New York Times.
This same article briefly discusses an even more deadly predator, with decades of movie fame: the shark. In comparison to the lion, the shark is said to kill more than 50% of the prey it seeks to attack. It is truly remarkable that the shark is a more successful predator than the lion by a factor of two.
What is absolutely astounding, however, is that a third natural predator catches more than 95% of the prey it goes after. This third predator is the main subject of Natalie Angier’s article, which is titled: “Nature’s Drone, Pretty and Deadly”. What is it?
Of course, it is the dragonfly!
Why else would I be writing about it? As the author of “Dragonfly Thinking” isn’t it important that I keep track of what is known about dragonflies? When I read the excellent article by Ms. Angier, I was taken aback. Until then, I had no idea that dragonflies were far more successful than sharks at catching prey.
One of the main reasons sharks are so effective as predators is their keenly attuned senses. According to How Stuff Works: http://science.howstuffworks.com/zoology/marine-life/shark3.htm, sharks were once thought of by scientists as “giant swimming noses”. The sense of smell of a great white shark is such that it would be able to detect a single drop of blood in an Olympic-size swimming pool.
Sharks also have a very acute sense of hearing, and they can employ electroreception (electrically sensitive receptor cells positioned under the skin in the shark’s head). Electroreception is not well understood, but it lets sharks perceive the weak electrical fields generated by living organisms. Not only that, but sharks have a special sensing organ called the lateral line, a set of tubes that run on both sides of the body that can detect nearby motion. When something comes near the shark, water runs through the lateral line, stimulating the sensory cells and alerting the shark to potential prey or predators in the area. These extra senses certainly play a role in the shark’s brutal effectiveness.
But how does the dragonfly do it? What makes the dragonfly so deadly? To get a feel for the capabilities of these little creatures, it is worth paying a visit to the wonderful online version of Natalie Angier’s article: http://www.nytimes.com/2013/04/02/science/dragonflies-natures-deadly-drone-but-prettier.html?pagewanted=all&_r=0. When you go there, you will see a short video of a dragonfly casually escaping as a bullfrog leaps in vain trying to catch it. The dragonfly is so far ahead of its predator that the video is almost comedic.
Ms. Angier writes: “Great white sharks have 300 slashing teeth and that ominous soundtrack, and still nearly half their hunts fail.
Dragonflies, by contrast, look dainty, glittery and fun, like a bubble bath or costume jewelry, and they’re often grouped with butterflies and ladybugs on the very short list of Insects People Like. Yet they are also voracious aerial predators, and new research suggests they may well be the most brutally effective hunters in the animal kingdom.” The new research Angier references came in a December 2012 article in Proceedings of the National Academy of Sciences (PNAS) by Paloma T. Gonzalez-Bellido, et al. The article attributes the greater than 95% predatory success rate to a special neuronal tracking system in the dragonfly brain.
Apparently, intercepting a moving object requires prediction of its future location, a complex problem that dragonflies solve using a group of 16 nerve cells, dubbed the “target-selective descending neurons.” They use these cells to track the location of the target with high accuracy and reliability. The results emphasize that a successful neural circuit for target tracking and interception can be achieved with shockingly few nerve cells.
Even more astounding is that dragonflies attend to multiple stimuli in primate-like style, concentrating first on one target while ignoring the others, and then suddenly switching full attention to the next target, and then if necessary, back again — rather as we humans can sequentially shift our focus at a busy party from one friend to another, or to a wineglass in need of a refill. Scientists have yet to determine what cues might prompt a dragonfly to decide, ‘Ah, there is the target I will pursue’.
So there’s more to the dragonfly’s amazing hunting skills than mere senses. As a dragonfly closes in on a meal, it maintains an image of the moving prey on the same spot, the same compass point of its visual field. Angier quotes a biomechanics expert named Dr. Stacey Combes, who says that, as a rule, the hunted remains clueless until it’s all over. “Before I got into this work, I’d assumed it was an active chase, like a lion going after an impala,” Dr. Combes said. “But it’s more like ambush predation. The dragonfly comes from behind and below, and the prey doesn’t know what’s coming.”
The dragonfly has clearly solved the problem of predation. It has the ability to focus intently on the insect of interest and ultimately catch this prey at least 95% of the time. Of course it is easy to say that the dragonfly is merely ambushing its prey, a less meritorious activity than hunting if we impose human morality. But by insect standards, brutal efficiency is the paragon of success.
The dragonfly does not have the superb multi-sensory apparatus of the shark. Dragonflies cannot smell very well and have very limited hearing, if they can hear at all. Yes, the dragonfly is a superb flier and can hover in exactly one spot for extended periods of time. It can fly upside down or backwards, turn on a dime, and zip through the air faster than any other insect. The dragonfly also has remarkable vision, probably the best of any insect. With multifaceted eyes covering most of its head, it can see you even after it flies past you. Flying ability, plus vision, plus persistence in tracking a target may be what produces uncanny success. Perhaps it is not an ambush but rather the result of an exquisite technique honed over hundreds of millions of years of evolution that enables the dragonfly to hunt so effectively: a technique involving focus, precision, and the ability to switch fluidly from one goal to the next. When we eventually cross the cosmos and visit other planets, I wonder if we will find any worlds teeming with life. If so, perhaps we will again meet up with dragonflies.
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