BEHAVIOUR 179 



these substances. Glucose and saccharose did not invoke consistent 

 responses, sometimes being taken, at other times not. It seems 

 from these resuhs, how^ever, that the food preferences of earth- 

 v^orms can be explained by the chemical sensitivity of the organs 

 of the body. 



The ability of earthworms to detect acids is of considerable 

 interest in another direction. It has been noted (Bodenheimer, 

 1934; Satchell, 1956) that many species of earthv^orms are absent 

 from acid soils. Each species shows a particular tolerance to 

 acidity, but has a lower ecological pH limit below which, apart 

 from a few individuals, it does not spread. It is also possible that 

 other factors may be involved in this avoidance of acid sites, for 

 example the low calcium levels allied to low pH may cause starva- 

 tion effects (Jefferson, 1956) or give rise to osmotic abnormalities 

 (Kopenhaver, 1937). The response of earthworms to acidity has 

 been demonstrated a number of times experimentally. 



Hurwitz (1910) was among the first to record what happens when 

 earthworms come into contact with acid. He suspended E. foetida 

 and allowed them to dip the prostomium into acid solutions, 

 noting the time taken to withdraw the anterior end from the acid. 

 The stronger the acid the shorter the time the prostomium spent 

 immersed in it. HCl was the most effective at causing retraction, 

 followed by nitric acid, sulphuric acid and acetic acid. The 

 concentrations required bore little resemblance to field con- 

 ditions. Neither did soils prepared by Arrhenius (1921) to have 

 known pH values, by treating them with acids. He isolated L. 

 terrestris and Perichaeta indica on these soils and found that 

 survival was longest on soils near the neutral point. Bodenheimer 

 (1934) using soils with a natural pH between pH 3 and 10 found 

 that the length of survival of Allolobophora samarigera was at its 

 greatest at around the neutral point of soil reaction. There was an 

 optimal range over which the earthworms survived equally well, 

 but it was pointed out that this optimal area may vary from species 

 to species. Indeed although A. samarigera and many other earth- 

 worms are not found in the field at pH lower than 4-5, 

 and indeed do not survive in such conditions, nevertheless Lum- 

 briculiis variegatus has been taken from acid sphagnum at pH 3-9, 

 and Bimastiis eisenii from peat moors at pH 3-7 (Satchell, 1956). 



Another reaction to acid may be the explanation of the results of 



