MILLIPEDES 21 



(Cloudsley-Thompson, 1951c). Under the inliiience of desiccation 

 the animals show positive geotaxis and move deeper into the soil. 

 Although the reactions of millipedes to moisture are far more 

 marked than are their responses to the humiditv of the atmosphere, 

 Shelf ord (1913) has shown that Font aria conugata is repelled by 

 dry air and more recently Perttunen (1953) has found that whereas 

 O. gracilis is very sensitive to differences at the higher end of the 

 humidity range, SchizophyUiim sabulosum, which has a much lower 

 rate of water-loss, particularly in summer, tends initiallv to move 

 towards dr^^ air and the reaction is gradually reversed to moist as 

 desiccation proceeds. Orientation is entirely 'kinetic' or non- 

 directional, speed is greater in dv}' air than in moist, and in an ex- 

 perimental chamber in which a choice of humidities is provided, 

 both the time spent and the distance covered are greater on the 

 moist side. In this species females that are just about to start Ci^i:;- 

 laying show a reversal of their humidity reaction and there is then 

 a clear and intense response to moisture (Perttunen, 1955). In a 

 similar way, during the summer, Polvzonium gcrmariicum walks on 

 the under surface of smooth chalk boulders, where it mav remain 

 for hours or days hanging on 'in a chiton-like manner with neither 

 head, antennae or legs exposed', but during the winter it pene- 

 trates into damp and compact vegetable matter and leaf mould, 

 frequently deep in moss, where it remains curled up for weeks 

 without moving. It is then dithcuk to find despite its bright 

 orange colour (Manton 1954). 



The response of millipedes to moisture has some economic im- 

 portance for, under conditions of drought, they may be forced to 

 attack growing crops for the sake of water. After some years' re- 

 search on the physiology and ecology of these animals, the writer 

 concluded that outbreaks of the 'spotted snake milHpcde' tend to 

 be stimulated by a dry spell following a period suitable to the re- 

 production of the species when the soil is damp, undisturbed and 

 rich in humus. It was shown experimentally that hunuis and rot- 

 ting substances have a texture which is preferred bv nulHpedes to 

 that of living plant tissues, and that the animals are attracted to 

 dilute concentrations of sugars. 



No doubt a moist season combined with the use oi farmvard 

 manure or the growing of some crop producing a considerable 



