22 MILLIPEDES 



amount of humus, will engender a great increase in the number of 

 millipedes in the soil, particularly if the ground is not disturbed by 

 ploughing, etc. They may be beneficial at this stage in aiding the 

 breakdown of the humus, but if the following season is dry, even 

 for a short spell, they may be compelled to attack crops for the 

 sake of moisture. Once an attack has been initiated, a return to 

 their normal diet of humus and decomposing matter is most un- 

 likely, due to the attraction of sugars in the plant sap. It is un- 

 likely that damage by millipedes to crops with tough exteriors 

 such as potatoes and mangolds can ever be primary, for not only do 

 their weak mouthparts prevent them from gaining access, but in 

 addition they are not attracted to unbroken skins of potatoes, only 

 to cut surfaces. Once an entrance has been achieved however, 

 through mechanical damage or the bites of wire-worms and other 

 pests, the millipedes will eat out the entire centre of a potato and 

 the damage they cause is often followed by fungal attack (Cloudsley- 

 Thompson, 1950a). Furthermore, the fact that single potatoes 

 have been found containing over a hundred Blaniuhis guttulatus of 

 all ages while the remainder of the crop was unharmed, shows 

 that they must have been attracted to a damaged tuber and could 

 not have bred there. 



Millipedes tend to avoid the light, but with the exception of a 

 directed response or 'taxis' away from light in those forms that 

 possess eyes and a response to gravity (which of course cannot be 

 other than directed since the stimulus is constant) the behaviour 

 reactions of millipedes are entirely non-directional. Oxidus gracilis 

 and Blaniulus guttulatus are without eyes but they possess a dermal 

 light sense. When illuminated they crawl around until by chance 

 they find themselves in darkness where they come to rest. Their 

 temperature reactions fall into three categories. There is a general 

 metabolic effect upon the speed of locomotion and duration of the 

 spiral reflex and a kinetic 'preference' for temperatures about 15° C, 

 while sudden drops of temperature engender intense locomotory 

 activity. Airborne odours are apparently not detected, but milli- 

 pedes respond to sugars by means of taste sense organs on their 

 antennae and mouthparts (Cloudsley-Thompson, 1951c). As they 

 walk about, millipedes steadily tap the surface over which they are 

 moving with the tips of their antennae and no doubt constantly 



