biology zoology blog fly cleaning

Better than TV and Computer Games

Better than TV and Computer Games – At least sometimes

I can understand that some people don’t like cockroaches (although, it should be mentioned that in 2000 E.M. Costa-Neto and M.V.M. Oliveira published an article in the journal Human Ecology Review, titled cockroach is good for asthma: zootherapeutic practices in NE-Brazil).

But cockroaches apart from being wonderful laboratory animals are also interesting to watch cleaning their long antennae. They seem to spend a lot of time on this grooming activity and it makes sense, for it is their antennae that are most important for them to explore their environment with. On them you would find sensors for smell, touch, humidity and temperature. They’ve got to be in perfect working order and therefore to keep them clean is of paramount importance to these insects. In ants their antennae are so important that in these social insects special rows of hairs and bristles on their legs are developed with which they can literally “comb” their antennae. Cleaning in ants is interesting to watch, as is the way how two ants when they meet will communicate by touching each other’s antennae.

However, if you put a live fly into a glass jar you will have something that may be even more fascinating to watch, especially for a child. The fly not only runs effortlessly up and down the smooth, vertical glass walls and even upside down across the lid (some spider do that, too), it also pauses now and then to wash itself – especially its feet, its face and its wings. This “washing” consists of a highly stereotyped sequence of activities, of which the scientists distinguishes 27 components. The two basic movements that are at the root of the fly’s cleaning behaviour are rubbing (for example, the rubbing of one leg against the other) and sweeping (a wiping movement of both legs across the under surface of a wing). Spiders have no wings but at times they do clean their legs and feet by pulling them through their mouths. The male whip scorpion actually holds the female’s long front legs in its mouth in courtship.

Back to the flies. They are proverbially “dirty insects”, frequenting unpleasant places and visiting faeces and corpses, they can be carriers of disease-causing bacteria, fungal spores and other spoilers of food. It would therefore not seem too surprising that they are in dire regular need of cleaning themselves. The cleaning, however, is not primarily directed towards the removal of microorganisms and parasites, but more a kind of preening to keep the body dust free, the wings operational, the eyes clear and the feet and their taste receptors on them sensitive (flies taste food with their tarsal receptors on their feet).

An introduction of a bit of chalk dust (or baby powder)into our jar demonstrates this convincingly. Immediately after that, the fly will spend a much greater proportion of its time on preening than before. And how precisely does it do that? First it rubs the front legs together; then it wipes the front legs over its head and its eyes (which, of course, must be kept dust free at all times (for vision is to a fly of the utmost survival value) and finally it may be the wings that need to be swept clean (and they too, of course, help the fly survive when facing danger). This sequence of action may well be repeated a few times, always starting with the front legs as if the fly was “washing its hands”. Once a child has seen all this, it will forever remember that even the “dirty fly” cleans its hands prior to washing its face and mouth and that afterwards it washes its hands again. What a nice teacher of our children: the humble fly.

© Dr V.B. Meyer-Rochow and, 2018.
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