INSECTS 45 



may-fly the larva has two or three tails known as " caudal 

 setae." In the adult these seem to be merely ornamental, 

 but in the larva they assist in breathing, and are important 

 organs. 



Under the microscope the setae will be found to be fringed 

 with minute hairs, and if the creature is alive the blood circu- 

 lation will be seen. Strangely enough, the blood is allowed 

 to escape from the vessel into the setae through small holes 

 in the former. 



The larvae of some species of may-fly live in ponds, others 

 prefer fast-running streams, and rest tightly pressed against 

 the stones, thus escaping the full force of the current. Some, 

 again, dig holes into the banks, and thus obtain shelter. 



Beatis fluminum is perhaps one of the commonest of the 

 may-flies that inhabit the fast-running, clear streams so 

 typical of hilly districts. It is a strange little creature, so 

 curiously shaped as to resemble a small but flattened lobster. 

 The gills are not fastened on to its back as in most other 

 species, but are attached to its sides. The limbs are broad, 

 the head large and semicircular. Pressed closely against 

 the stone, Beatis fluminum vibrates its leaf-like gills and 

 shows a great unwillingness to move unless forced to do 

 so. Then, with a suddenness that easily baffles its would-be 

 captor, the larva rises and runs rapidly, and taking advantage 

 of the nearest cover disappears. Beatis is carnivorous, and 

 preys upon smaller aquatic creatures. 



Another species very often found in fast-running streams 

 is Ephemerella. This little animal has the common sense or 

 common instinct to cover its body with mud, thus deluding 

 both its enemies and the small creatures on which it feeds. 

 It will be interesting to followers of Isaac Walton that the 

 larvae of the " drakes " Ephemera vulgata and E. danica live 

 in burrows in the banks of rivers and streams. Their food 

 consists of finely-divided organic debris. They seem to prefer 

 streams in which clay forms a noticeable part of the banks. 

 May-fly larvae, as far as it is known, all live a life similar in 

 general details, although differing to some extent in their 

 habits. 



The day eventually comes when the larvae which have 

 escaped their numerous enemies fishes, water-beetles, and 

 carnivorous members of their own order leave the water. It 

 may have been one, two, or perhaps three years since the 

 larvule first made its appearance, and now the day has come 

 when hundreds of thousands of larvae rises slowly towards the 

 surface. Each skin opens along the back, the head gradually 



