Wednesday, 15 August 2012

In praise of rat tails

The other week, a fellow wildlife gardener tweeted her delight at attracting rat-tailed maggots to her nettle feed. It might seem an odd thing to be delighted about but not if you are a gardener and happen to know what these unpleasant-sounding creatures turn into. Rat-tailed maggots are the larval stage of certain hoverflies and hoverflies, as any wildlife gardener will tell you, are considered to be great allies in the garden.

Looking rather, well, ‘maggot-like’ these larvae get their name from the long breathing tube at their rear. A number of different hoverfly species produce larvae of this form, including the familiar drone-fly Eristalis tenax, which (as an adult fly) mimics a bee. In some species the ‘tail’ can be several centimetres in length, allowing the larva to remain hidden in the detritus that gathers at the bottom of a pool while still enabling the larva to take air from the surface. rad-tailed maggots are typically found in stagnant water, such as that which forms in farmland ditches or garden water troughs. Others make use of slurry, rot holes in trees and sap runs; it is easy to see how nettle feed emulates some of these peculiar habitats.

Not all hoverfly larvae live such a damp existence though. Some live under bark or within dead wood, while others live on the surface of plants where they hunt aphids – something which may seem surprising for a maggot-like creature lacking legs. It is these aphid-eating larvae that are really the gardener’s friend, rather than the other species that have no impact on potential pest populations. There are even some species that, dare I say it, feed on plants! Each of these larvae tends to show adaptations to its particular way of life. Aquatic species, for example, may have modified mouthparts that enable them to filter feed and to take organic matter from the ‘soup’ in which they live.

Quite a few species have larvae that are similar in appearance so that, even with a guide (believe it or not there is a field guide to these creatures) you have to rear them through to adulthood in order to find out what you have been looking at. I am not quite sure that I am ready to have a go at those species that live in manure or slurry but I think I could manage some of the stagnant water or dead wood forms. It is amazing to discover this part of the hoverfly lifecycle and to find creatures making the most of the opportunities that these rather unusual microhabitats provide. It is also amazing to see the adult hoverfly and to know just how very different things were when it was a larva.

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