Sunday, 10 February 2008

Life in a hostile habitat: the wing of a bat


For several years I have been taking a close interest in bat parasites. Indeed, as I write this, to the side of my laptop are a stack of specimen storage vials containing over 400 parasite specimens, taken from over 80 individual bats.



Many of my bat-worker colleagues find this interest hard to understand. Admittedly, they do not fall into the charismatic megafauna "cute and cuddly" bracket, but many are impressive animals in their own right.


Spinturnicidae are the largest and most obvious of the mite families, which use bats as their hosts. Superficially like miniature claw-less crabs, they live out their entire lives on the wing and tail membranes of their host, never leaving the bat, except to pass to a new host. Unlike many ectoparasites, they do not take refuge in the bat’s fur.



The wing membrane is a mind-bogglingly hostile habitat: in flight the wings flap 10-15 times per second, requiring immense grip and an aerodynamic profile to stay attached. Like all mammals, bats regularly groom themselves, and unable to hide in the bat's fur, these mites need to make it difficult for the bat to dislodge them from the wing. Vulnerable eggs or larvae would not survive long.


To survive in this difficult habitat Spinturnix mites have several adaptations:
  • Their short, stout legs are extremely strong.

  • Feet are equipped with large claws and sticky-hooked pads, to cling on.

  • The body is flattened and armoured with chitinous plates.

  • Egg & larval stages are completed within the female's body.

  • The female gives birth to a single protonymph,

Removing Spinturnix specimens from the bats is an uphill struggle. As soon as the mite realises it is threatened it either runs across the wing membrane (and they're fast), or it hunkers down and grips the membrane tightly. Either way, the best way to remove them without risk of harming the bat is to dab it with a drop of ethyl acetate or 70% alchohol, which usually dampens it's ardour.


Having gone through the difficult processes of catching a bat, then removing the mite, the fun is only beginning! Attempting to identify of bat mites has led me to seek documents published by the Zoological Society of London in 1923, by the University of California in 1960, and most recently a Russian-language parasitology journal! But it's all good, clean fun....
Pictures:
Top - Daubenton's Bat Myotis daubentonii, showing the wing membrane.
Middle - Close up of the wing membrane, with a Spinturnix myoti mite.
Bottom - Adult female Spinturnix myoti.

Anyone wanting to study bat parasites in the UK is lucky to be able to draw on the work of Anne Baker of the Natural History Museum. With Jenny Craven of Leeds University she produced a checklist of species in 2003, which is available on the web: http://www.nhm.ac.uk/hosted_sites/acarology/saas/saasp/2003/saasp14.pdf

Please note, trapping, handling or otherwise disturbing bats in the UK is illegal without a licence from one of the statutory nature conservation organisations (SNH, CCW, Natural England).

My website: plecotus.co.uk

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