CHAPTER VI 

 SIALIDAE 



THE ALDER FLY (SIALIS) 



ONE of the very commonest of aquatic Insects is 

 the larva of Sialis lutarius. It is found in ponds and 

 slow streams. A muddy bottom is one requisite ; 

 hence Linnaeus' specific name, lutarius, which means 

 muddy. The larva creeps about actively on or in the 

 mud, seeking its food, which consists of other aquatic 

 animals. I find that in captivity it will eat Caddis- 

 worms and Ephemera-larvae, and authors mention 

 having found fragments of Insects in the alimentary 

 canal. The length of a full-grown larva is about an 

 inch, and the greatest width one sixth of an inch. 

 The body tapers a little towards the head, and very 

 gradually to the slender and long-drawn-out tail. 

 The six legs are strong and well suited to walking. 

 Each ends in a tarsus of two joints, bearing a pair 

 of pointed claws. The head is provided with a pair 

 of antennae, a pair of long, curved and pointed man- 

 dibles, which sufficiently indicate the carnivorous 

 habits of the larva, and the other mouth-parts usual 

 in biting Insects. From the sides of the first seven 



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