480 
The Biting of Mosquitoes 
encourage the idea that the smell of the sweat was attractive either to 
G.fatigans or to S. scutellaris. 
The following are some of the attributes of a living warm-blooded 
animal which may be supposed to advertise its presence to an insect 
such as a mosquito. 
(1) Motion. Probably unimportant. Mosquitoes bite a motionless 
sleejDer. 
(2) Form and colour. They are very obviously attracted by black 
and dark colours (it is remarkable that tsetse-flies are similarly attracted 
by black), but pay no regard to form as far as can be seen. The fact that 
black objects are good absorbers and good radiators of heat may be not 
without significance (see below). 
(3) Smell. Blood and sweat without apparent influence. 
(4) Temperature and air-currents due to the motion of air warmed 
by the body. 
With regard to this last (No. 4), it is obvious that the lighter an 
insect is, or rather the greater its surface area in proportion to its weight, 
the more susceptible to air-currents is it likely to be. Since the volume 
(and therefore the weight) of solids varies as the cube, and the surface- 
area as the square of the linear dimensions, the ratio for two 
insects of the same shape will be, roughly speaking, inversely propor¬ 
tional to their respective lengths: that is to say, an insect 2 mm. long 
will expose five times as much surface in proportion to its weight as a 
Fig. 1. Besting attitude of (a) Mucidus scatophagoides, (b) Phlebotomus hahu, both from 
photographs (not drawn to scale). 
