Wednesday, 24 July 2013

Science Fiction ? Science Fact !

With the school holidays so far going as predicted (ie no time for dragonhunting) I thought I'd do a bit of investigating instead (a dragonhunter is never off duty).
Since being captivated by the scene in which a female Emperor captured and devoured a Four-spotted Chaser at Kibblesworth last week, I thought I'd do some reading up into what makes dragonflies the top predator they are in the insect world, and I found some quite startling facts and science about the inbuilt hunting tools which makes them probably the most efficient predator for their size that Mother Nature has ever produced.  

They are the stuff of science-fiction, cyborgs on a small scale; voracious hunters with an incredible success rate of over 90%, which is pretty amazing when compared with other top predators. Sharks for example have a success rate of around 50%, lions only 25%. So how do they do it?
Quite simply they are equipped with tools for hunting which put them light-years ahead of their competitors and their prey. If it wasn't for the fact we know they are millions of years old, we'd probably think they were from the future. Read on and be amazed :

The killing spree starts off at the larval stage. A diet of small aquatic insects and larvae in most cases, but larger nymphs will extend to tadpoles and small fish. They have an incredibly powerful extendable jaw which acts like a harpoon, shooting forward to capture prey, (apparently where the idea for the creatures in the Alien films came from).
And I’ll bet you didn’t expect to hear this, but they also have a specialist predator arsehole (!) Not only do they breathe through their anus but they also shoot jets of water from there which enables them to torpedo through their aquatic environment in pursuit of a meal, or to avoid being one. How cool is that?

But it is as adults where their advanced technology puts them way ahead of any other insect on the planet.

Let’s start with those massive bulbous eyes, wrapped around the head resembling a starfighter pilot’s helmet. Most insects have multifaceted (or compound) eyes. Your average housefly has around 6000 facets and is difficult enough to sneak up on, a dragonfly has 30,000!
Each facet creates an individual image which the dragonfly brain transforms into one 360 degree picture, meaning the dragonfly blind-spot (behind and below) is tiny compared to most other insects, so that when you try to sneak up on a dragonfly, you only get close if the dragonfly wants you to, an invaluable tool in avoiding predation as well.

They view life through the normal colour spectrum as we do but also see UV light and the plane of polarization, aiding navigation and giving the effect of built-in sunglasses (handy when you tend to hunt mostly in sunshine).

Bionic Eyes

And it doesn’t stop there; in the simple nervous systems of most insects, multiple objects tend to fade out as the insect can’t handle the attention multitasking. But dragonflies have the ability to switch their attention between objects at will. This selective attention span allows the dragonfly to single out one target in a swarm, then zero in on it exclusively, while remaining aware of the rest of the swarm to avoid a collision.
But best of all the compound eyes also provide the dragonfly with a targeting system in that when they hunt, they can section off part of the eye and use it like a grid (a bit like on the x-wing or tie fighters in Star Wars), keeping the target in the same section of the grid as they approach, making it incredibly accurate.

However it’s not just visual awareness which gives dragonflies their ruthless predatory efficiency. They have many more weapons in their armoury as well.
Speed and agility is one of their most distinguishing features and this comes down to the way their wings work. Their four wings operate independently of each other, allowing them to manoeuvre in mid-air like a helicopter. They can hover, fly forwards, backwards, sideways, and instantly change direction whenever they need to. Dragonflies can even fly upside down if need be, the only insects with this amount of control over their wings.
The wings themselves are delicate yet powerful, each wing is connected to the thorax by a separate muscle group, beating at a rate of around 30 times per second to propel them through the air at speeds of over 20 and in some cases 30mph with a rate of acceleration which to your average insect would be like going into hyper-drive.

Each wing powered by its own engine

So what happens when they intercept their prey? Like all insects, dragonflies have three pairs of legs, but you won't see a dragonfly walking. The three pairs increase in length from front to back and are covered in stiff bristles. They have evolved in different lengths so each pair can curl forward and have the same reach, clamping around the victim, bristles forming a cage and preventing escape.
With victim secured, their hinged jaws bear down and shred the wings off the fly, immobilizing it, and after that they’re free to chew away without any chance of losing their prey. They often consume their food in mid-air without even bothering to land, and can feed in this way tirelessly for long periods, not only satisfying their hunger, but storing food in their large crop for those days the sun don't shine.
Legs ensnare the victim like
a bear trap 

Their staple diet is small flies, but dragonfly jaws can open as wide as their head, allowing them to eat virtually anything within reason, even in some cases other, similarly sized dragonflies. Their scientific name Odonata is Greek, meaning ‘toothed ones’ in reference to their powerful serrated jaws which can slice through the exoskeleton of a victim like industrial metal-cutters on an aluminium sheet, or simply crush it to pulp. Only the largest hawkers have a bite powerful enough to break human skin, but to a fly it’s like being put through a car crusher.

Jaw breaker !

All these physical attributes help give the dragonfly a reputation for ruthlessness which would  give Darth Vader a run for his money, but the one truly amazing thing I discovered is their mental capacity for their size.
If you've watched a dragonfly hunting, you'll have noticed that a hawker just seems to pluck a victim out of the air with consumate ease, or a darter will fly up from its perch, snatch a meal out of the sky, and return to base, making it look so easy.
This is because despite their high speed they don't need to chase down their prey like a sparrowhawk or stoat for example which rely on stealth to get close then speed to make the final kill; they intercept it out in the open. 
And the dynamics of capturing something in mid-air are staggeringly complex for an insect, so much so that it's usually something only done by animals with complex nervous systems like birds and mammals. In effect dragonflies ensure a kill by predicting where their prey is going to be, indicating that they have the capacity to consider the distance, speed and direction of their quarry, and in the space of milliseconds will calculate the angle of approach, so like a sci-fi horror movie monster, is already waiting while the hapless fly stumbles right into its clutches, fate sealed by those terrifying jaws. . . . and as we found earlier, with a 90+% success rate . . . . staggering!  
 
The more I learn about dragonflies the more I admire these fascinating creatures. They have all the tools necessary to get the absolute maximum out of their short adult lives, they really are out of this world!

5 comments:

  1. Wow, very interesting read :)

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  2. Excellent Alan, some fascinating facts, and I can confirm that a Southern Hawker can pierce my skin.

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  3. I knew most of those facts but a few more chucked in with brilliant articulation made for a cracking read. Just back from the Lakes without any new species of Dragons but did have first Black darter. I had quite a few sites marked down but I got side-tracked most of the time and ended up elsewhere but I had a fab but exhausting three days. On the go from 5a.m. till 9.30 p.m. each day. I'm KNACKERED. But very happy.

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  4. Absolutely fascinating and you made it a great read putting it in words of one syallable (sometimes) so that even Mr Kinson could understand it.

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  5. Cheers everyone, I think it's their half-living/half-machine look which has fascinated me from observations over the years so couldn't resist the sci-fi comparison when finding a few extra facts, especially after watching all the Star Wars films with the kids lately.
    So thanks for your comments,appreciated.

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