216 



NOTE ON THE CHEMOTROPISM OF THE 

 HOUSE FLY 



By W. K. G. ATKINS, Sc.D. 



{Sometime Experimental Officer, Royal Flying Corps.) 



The following notes have been called forth by the perusal of two recent 

 papers in this Journal, viz. those by Imms and Husain (1920) and by 

 Speyer (1920). The observations were made mainly at Aboukir, on the 

 north coast of Egypt between 1916 and 1919. As may be imagined, the 

 aim in view was the destruction of the flies, and the haphazard experi- 

 ments were carried out in addition to much other work and with no 

 thought of pubUcation. They, however, appear to confirm the observa- 

 tions of the above-mentioned investigators by trials on a large scale. 



It was found that formaHn, when dilute, was at times very effective 

 if exposed in a shallow dish near a window. The presence of a little bread 

 or something to give the flies an ahghting ground increased its usefulness. 

 Flies apparently drink in the morning^ , as early as possible, and for this 

 reason the formalin should be available at that time. When allowed to 

 stand in the hght, formaldehyde changes into one of its solid polymers, 

 as may be noticed when tha solution evaporates. The latter, however, 

 appears to be poisonous to flies, though no direct observations were made 

 on this point, a little formalin always being present. As pointed out by 

 Morrill (1914) the behaviour of formalin in attracting flies is very variable. 

 If too strong they appear to be driven away and in the presence of 

 miscellaneous foodstuffs they will usually leave a formaUn solution un- 

 touched. 



As noted by other observers, beer is a very attractive substance to 



flies. It was found that dome-shaped glass vessels with a rim turned 



up inwards made excellent traps when the annular trough was filled 



with beer. The domes were supported on three legs and placed for 



preference in the sun or a well-Ughted position. The number of flies 



caught in such traps within two hours of their first being tried at Aboukir 



was quite amazing. These traps were not, however, available in any 



quantity, nor were the Japanese clockwork traps, so attempts were made 



to render weak formalin more attractive by adding cane sugar, also 



^ The water supply of the numerous beetles inhabiting the patches of baked claj' in 

 the coastal deserts was a puzzle to the writer till it was noticed that they drank drops of 

 dew from the angles of diied-up thorny plants. 



