164 WOTTON : LIFE-HISTORY OF ARION ATER, 



In common with other slugs, this species is infested with a 

 small white parasite, which occasionally visits it in considerable 

 numbers, darting about over its body and in and out of the 

 pulmonary cavity without ever seeming to rest. I have noticed 

 a quantity of them swimming about on the water after their 

 benefactor has taken a bath ; probably the Arion resorts to this 

 expedient to rid itself of its strange guests when they become 

 too troublesome. 



Once more reverting to the eggs. On carefully weighing 

 them^ I found there were 624 to an ounce. This was exactly 

 the weight of the light-yellow slug just before it commenced 

 depositing. In excluding 246 eggs, it parted with three-eighths 

 of its own weight in thirty hours; whilst from Oct. 13th to 

 Nov. 30th (forty-eight days) 477 were produced, the total 

 weight of this number being slightly over three-fourths of the 

 weight of the parent slug. What astonishing fecundity ! 



Considering the quantity of eggs produced, it seems sur- 

 prising that there should not be a plague of slugs ; but they are 

 not nearly so numerous as the above facts would seem to 

 warrant. Let us now consider the causes that effect their 

 reduction. 



In the first place, very many of the eggs prove naturally 

 unfertile; then the parent often turns cannibal and devours them, 

 or, for the matter of that, the eggs of any other species — it is not 

 at all fastidious in this matter. Again, centipedes, ants, and 

 other insects prey on them ; but the greatest enemy of all is the 

 larva of a small fly, which punctures a minute hole in the shell, 

 wriggles itself inside, and eats out the interior. These larvae 

 occur at times in such vast numbers that the earth in particular 

 spots has the appearance of a moving mass of life ! Many a 

 nice batch of eggs I have had destroyed by this industrious 

 creature, and many are the expedients I have employed to 

 crush it out, but without success ; it is so perseveringly persis- 

 tent. Lastly, come the birds, who pick off the infant slugs 

 whenever an opportunity occurs. So, between the constant 



J.C, vii., Apr. 1893. 



