SCIENCE-GOSSIP. 



THE LABOUR OF LOBWORMS. 



By Charles Davison, M.A., F.G.5. 



"CpEW, if anv, of Mr. Darwin's books have 

 *■ appealed more strongly to the popular taste 

 than the last of all, the well-known work on " The 

 Formation of Vegetable Mould, through the 

 action of Worms, with Observations on their 

 Habits." Interesting as the whole volume is, one 

 of the most remarkable facts established by 

 Mr. Darwin is the great quantity of earth brought 

 up by worms to the surface. Squares, generally of 

 a vard each side, were carefully measured off, and 

 the castings formed on them were removed, dried 

 and weighed. At the end of a year the total amount 

 of earth thus collected was found to be equivalent 

 to a weight of from seven and a half tons to eighteen 

 tons per acre. If it had been spread out over the 

 surface, without any loss from wind-drifting or other- 

 wise, it would have formed a layer from one-tenth 

 to about one-sixth of an inch in thickness. 



All who are accustomed to walking along a 



sandy beach are familiar with the appearance it 



presents when the tide goes down. The whole 



surface in places is then thickly dotted over with 



the castings of the lobworm or lugworm, Arcukola 



I atontm, so called from its frequent use as bait. 



So closely are the castings sometimes collected, 



that from a distance the sand looks as if covered 



with a rash. When we reflect on the enormous 



numbers of castings thus thrown up, and then 



remember that as the tide advances they are all 



obliterated, only to be renewed as the water again 



retires, the vastness of the work accomplished by 



the lobworm •will be easily apparent. A few years 



ago I endeavoured to estimate roughly the number 



of castings thrown up in a given area, and also 



the weight of sand contained in them (Geological 



Magazine, vol. viii., 1891, p. 489). My observations 



were made chiefly on the bread stretch of sand, 



three miles wide, which at low tide separates Holy 



Island from the opposite coast of Northumberland. 



The}- were, however, confined to a short visit of 



only a week in August, 1891, and as it seems 



possible that both the number and weight of 



castings maj* vary much at different times of the 



year, I propose to describe here the methed 



adopted and some of the results arrived at, in the 



hope that others who live near the sea may be 



induced to carry on similar observations at regular 



intervals throughout the year. 



The implements required are few and of the 

 simplest description — a measuring tape (one that 

 will not stretch is essential) ; a small shovel with a 

 sharp edge and flat bottom, which can be easily made 

 to order ; one or more wide-mouthed jars or bottles 

 (say two- or three-pound marmalade jars), and 



some pieces of oiled silk to cover them ; the whole 

 costing about a shilling. Being provided with 

 these, we prcceed to work. We select a stretch of 

 sand where castings are clustered with a fair 

 approach to uniformity, and seem to be neither 

 more nor less abundant than in surrounding parts. 

 If the spot can be identified so as to be used on 

 subsequent occasions, so much the better. With 

 a stick we mark out a triangular area, making the 

 sides as straight as possible, and each about four 

 or five yards long. The reason for choosing a 

 triangular area is that we have only three sides to 

 measure, and one area to calculate. If a four- 

 sided area were employed, we should have to 

 measure five lengths (the four sides and a diagonal), 

 and to calculate two areas, as we cannot be certain 

 that the sides are all at right-angles to one another. 

 We then count the number of castings within our 

 selected spot, marking off small spaces in regular 

 order round the sides, so as to count more easily 

 and accurately; and lastly, we measure the lengths 

 of the three sides. These data are sufficient to 

 determine the average number of castings thrown 

 up over any required area, say one acre. If we 

 wish to ascertain also the weight of sand contained 

 in them, we gather as many castings with the 

 shovel as the jar will hold, taking care to select 

 those which seem to be of the average size, for it 

 will be found that their dimensions vary even 

 within a very small area. 



The following data should be entered in a note- 

 book as soon as they are known : The position of 

 the selected area, the lengths of its three sides, the 

 number of castings contained within it, the num- 

 ber collected for weighing, and an}' other remarks 

 as to size, uniformity of distribution, and others 

 which may appear desirable. If possible, several 

 observations of this kind should be made after the 

 same tide, and on the same or a neighbouring 

 stretch of sand. The greater the number of obser- 

 vations, the more likely are we to eliminate errors 

 due to our selection of areas and castings, and the 

 more accurate, of course, will be the results 

 obtained. As the number of jars we can carry is 

 limited, we cannot expect to collect castings from 

 more than three or four areas on any one day, but 

 there is no limit, except the time at our disposal, 

 to the observations on the number of castings. 



As to the time when the measurements should 

 be made, I do not think much care is required, 

 though it might be desirable to inquire into this 

 point. I was unable to make very careful observa- 

 tions myself, but I am under the impression that 

 few, if any, castings are ejected on the surface after 



