Sunday, 21 April 2013

In praise of craneflies

Here are some curious creatures from Hauxley last week. Scott spotted the left hand one as it lay, elegantly submerged, just beneath the surface of a pool. At the hind end a corona of short tails clad in a dense fur of water repellent hairs breaks the surface tension and allows the creature to replenish its air supply. The other two maggots turned up later in the week, at first glance apparently the same species but the middle one has tails festooned with wispy tufts, whilst, on the right, the larva ends with delicate lobes and what look like two eye spots but are the opening plates leading into the trachae breathing tubes that ramify the length of the body. That left hand one is substantial: 3cm of ominous twitching, a small head reaching back and forth, the jaws gnashing. The other two are not so big but, again, you can see the retractable dark head and mandibles. All three are larvae of craneflies (the family of flies called Tipulidae). Cranefly maggots thrive in damp soils, swamps and ponds, shredding leaves and other detritus with those tough jaws. They are not glamourous insects. There is not a Cranefly equivalent of the British Dragonfly Society or Balfour Browne Club (a sort of train-spotting club for water beetle enthusiasts. I should know, I've been a beetle train-spotter for 30 years). I do not know precisely which species these craneflies are (I don't know imprecisely either, to be precise), nor much about what they do, the habitats they prefer or why they should turn up this year but not last. The larger one was widespread in the Hauxley ponds this week and grown fat on what they offer. When the behaviours of pond invertebrates have been observed in detail they commonly show complex and nuanced natural histories, with precise behaviours and tolerances: for example, where water boatment will or will not lay eggs or damselflies changing behaviours in response to different predators and water beetles sensitive to changing structural densities of weed beds. These cranefly maggots are probably just as particular in their ecologies but remain mysterious.

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