influence of temperature and light 83 



The Influence of Temperature. 



The inrim-nce of temperature on the development of the larva 

 and on the life-history will shortly be discussed. Temperature 

 also directly affects the adult insect ; house-flies are most active at 

 a high summer temperature and their metabolism is correspond- 

 ingly active. Cold produces inactivity and torpor. They are able, 

 however, to withstand a comparatively low temperature. Bach- 

 metjew (1906) was able to submit M. domestica to as low a 

 temperature as — 10° C, and vitality was retained, as they recovered 

 when brought into ordinary room temperature. Donhoff" (1872) 

 performed a number of experiments previous to this ^v^th interesting 

 results. He submitted M. domestica for five hours to a tempera- 

 ture of — r5° C, and they continued to move. Exposed for eight 

 hours to a temperature of first — 3° C. and then — '1° C. they moved 

 their legs. On being submitted for twelve hours to a temperature 

 first of — 3-7° C. and then — 6'3° C. they appeared to be dead, but 

 on being warmed they recovered. When exposed for three hours 

 to a temperature of — 10° C. which was then raised to — 6° C, they 

 died. These experiments show that M. domestica is able to with- 

 stand a comparatively low degi'ee of temperature. 



The Influence of Light and Colour Preference. 



The adult house-fly seeks the light, that is, it is positively 

 heliotropic, and as Felt showed, is unAvilling to enter very dark 

 places to deposit its eggs, although in placing the eggs it endeavours 

 to place them as far away from the light as possible. 



A series of experiments were carried out by Galli-Valerio (1910) 

 with a view to ascertaining whether flies had preferences for certain 

 colours. Flies were placed in a cubical glass-sided box measuring 

 35 cm. each way. On the sides of the box pieces of coloured paper 

 of equal size were pasted. The flies resting on the diff"erent colours 

 were then counted, the cage being turned in different positions to 

 avoid error. The colour preferences which he found were as follows, 

 the preference for clear light colours being strongly indicated : 



Clear green 18 Azure 13 



Rose 17 Clear red 10 



Clear yellow 14 Dark gi-ey ... 9 



6—2 



