Wednesday, 21 May 2014

The Gory Details . . .

Finally got round to watching 'Insect Dissection' last night after recording it a couple of weeks back. Fascinating (if gruesome) stuff, and answered another dragonfly question I'd wondered about for a while.
Like how do they feed during periods of shitty weather in the summer? As from what I see and read, if they aren't involved in some part of the reproductive cycle all they seem to do is eat, but when the sun ain't shining they don't even come out of hiding. So how do they survive, or do they just starve to death?

Well no, apparently the insect digestive system (though a lot like ours) also contains a sizeable crop, so most of those insects they chew and swallow are stored for (literally) a rainy day, and in this way they can survive for some days without eating. Simple, but another mystery solved. :-)

Other things of note in the programme, they asked why dragonflies are the size they are today whereas millions of years ago some had wingspans of a metre or more. It's well documented that it has to do with the amount of oxygen present in the atmosphere. In dinosaur times it was 30% nowadays it's nearer 21%.
Oxygen powers all the functions and is carried to all the muscles and organs by an intricate network of tracheal tubes, and it seems to be a case of the bigger the insect, the more of these tubes it needs to get the right amount of oxygen to function properly, so they have reached their maximum size for the oxygen levels of today.
To prove it they did an experiment at Harvard with a darner dragonfly (a hawker on our side of the pond) whereby they reared one in artificial conditions containing 30% oxygen, with the startling result that the emergent dragonfly was almost 25% bigger than the parent (and that was just a single  generation). Of course the poor bugger ended up pinned to a board to show size comparison, but never mind, all interesting stuff.

Another fact I found out, the muscles which power the wings take up practically the whole of the thorax, with massive air-sacs in the centre to fuel them (as this was part of the dissection I can safely say I saw the whole lot in its gory glory), and the muscles themselves make up around 60% of the total bodyweight of the insect, showing just how much power they must need.

A lot more general stuff too but very interesting it was. I always thought insect innards were just a pale yellow mush which somehow caused the insect to work, but no, they function very similarly to us, with microscopic nervous, digestive, respiratory and muscle systems in amongst the pale yellow mush, which is actually just the stored fat.

But to finish, the ghoulish image (surprise surprise) was about the cockroach, which has a nervous system running through the length of the body in nodes like tiny brains, meaning that if the head is cut off it would continue to run around, until it eventually starved to death.

Don't have nightmares :-)



  1. Missed the programme,sadly, and it's not on i player but did manage to see a couple of clips. Hopefully it might be repeated at some stage.
    Dragonflies are the dogs. The more you learn about them.......
    Quite a bit from your good self. Keep it coming.

    1. Cheers John, it's worth watching if you get the chance, if just for the micro-photography.