Nick Baker’s Hid­den Britain

Re­veals a fas­ci­nat­ing world of wildlife that we of­ten over­look.

BBC Wildlife Magazine - - CONTENTS - NICK BAKER NICK N BAKER a nat­u­ral­ist, author and TV pre­sen­ter.

In the depths with drag­on­fly nymphs

You’re likely to en­counter drag­on­flies and dam­sel­flies any­where there is fresh wa­ter – and of­ten some dis­tance away, too. For a cou­ple of heady months, mem­bers of this gauzy­winged, so­lar-pow­ered su­per­group, the Odo­nata, are among the most prom­i­nent and ex­cit­ing in­sects on the wing.

The tal­ents of adult drag­on­flies and dam­sel­flies are of­ten talked about. They boast in­cred­i­ble vi­tal sta­tis­tics: the most lenses (up to 30,000 per eye) of any in­sect, and prob­a­bly the fastest level flight too (some species reach over 48kph). Yet most of their life is spent in the wa­tery realm.

Now is the ideal time to go on a baby dragon hunt – all you need is a pond net and a tray or tank. But while their par­ents are mas­ters of the air, these aquatic me­chan­i­cal mon­sters are the lords be­low the sur­face. They lurk at the bot­tom, un­no­ticed by all but cu­ri­ous pond-dip­pers.

Both drag­on­fly and dam­sel­fly lar­vae, known as nymphs, are as preda­tory as their par­ents. Large eyes, elon­gated bod­ies and, in the case of dam­sel­fly nymphs, three leaf-like ‘tails’ (ex­ter­nal gills) make them easy to iden­tify. If you keep one in a tank with a few other pond crea­tures and keep a close eye on it, you’ll see a spe­cial form of skul­dug­gery. To see this you need to pay close at­ten­tion as it’s over fast.

Within 10–30 mil­lisec­onds, the front of the nymph’s head ap­pears to fly off to grab its prey, be­fore re­tract­ing to dis­mem­ber the vic­tim. This ‘mask’ struc­ture is dif­fi­cult to see in liv­ing an­i­mals, but look at reeds for empty nymphal cases and you will see it more clearly.

If the ex­u­viae is soft, wet and not too crispy (you may want to soak it in warm wa­ter), you can pull out with a pin the weird el­bow un­der­neath the head to re­veal a swing arm tipped with a cou­ple of hinged, stiletto-like spikes. This de­vice is unique in the in­sect world.

An­other pe­cu­liar­ity of drag­on­fly nymphs is that you’ll no­tice they don’t have three tails like dam­sel­flies. That’s be­cause theirs are lo­cated within their bot­tom. Not only do they breathe through their anus, but it is also used to good ef­fect in other ways. Thanks to mus­cu­lar con­trol of a di­aphragm and an anal valve, the lar­vae can draw wa­ter in through their rec­tal cav­ity – use­ful if you want to ‘breathe’ ac­tively and not de epend on pas­sive ab­sorp­tion of ox xy­gen over a gill mem­brane.

I’ve al­ways been fas­ci­nated by y the power of drag­on­fly n nymphs’ jet bot­toms. I used to lo ove watch­ing a nymph squirt its way w around in a tank, and even di irect a jet of wa­ter into my eye w when plucked from the sur­face. B Best of both ends It t may seem that these two sk kills are un­re­lated, given they in nvolve dif­fer­ent ends of the bo ody, but it turns out that one of th he rea­sons a drag­on­fly nymph ca an ping its mask for­wards at su uch an im­pres­sive speed is by si imul­ta­ne­ously clench­ing its anal va alve, thereby stop­ping wa­ter be eing ex­haled, and con­tract­ing it ts ab­dom­i­nal di­aphragm. This ca auses an in­crease in fluid pr ressure in the nymph’s body ca avity, to around 0.87 psi.

This pres­surised blood, or r haemolymph, has to find so ome­where else to travel. The in ncrease in hy­dro­static pres­sure fo or­ces blood into the labial mask, th hrust­ing it for­wards. There is al lso a trig­ger-like mech­a­nism – a ‘bio-spring’, that stores mus­cle en nergy and holds the mask in pl lace, and this is also re­leased. T The re­sul­tant force is enough to o al­most guar­an­tee din­ner.

There be dragons: drag­on­fly nymphs are fe­ro­cious preda­tors with a light­ning strike.

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