HYMENOPTERA SAW-FLIES, ETC. 



185 



Croesus septentrionalis, Leach (Cameron). 

 Nematus septentrionalis, L. 



This species is said to he very common in some parts of the country ; 

 and Cameron says the larva? feed on poplar, aspen, hirch, willows, 

 hazel, and mountain ash. I have not, however, found it on any 

 of these plants, hut in Cheshire it was very common on, and 

 sometimes quite injurious to, alder. 

 Fig. 174 is from a photograph on 

 alder. 



The perfect insect may easily he 

 recognised by the peculiar flattened 

 formation of the tibiae and tarsi 

 (fig. 175 a), and black colour of the 

 hind legs. Head and thorax black, 

 abdomen black and brown, antennae 

 large as the body. Wings 



as 



Spread of 

 male and 24 



wings 



16 



mm. 



in 



hyaline, 

 mm. in 

 female. 



The larvae (fig. 175 b) are bluish- 

 green, with black head ; head, ex- 

 treme end of abdomen, and prolegs 

 quite yellow ; one or two rows of 

 black dots along the body. Length 

 about 30 mm. 



The perfect saw - fly is a black 

 and light-red insect. In both sexes 

 head, thorax, and anal portion of 

 abdomen black ; remainder of abdomen light-brown. Wings hyaline ; 

 stigma in female black, in male light - brown. Length of male 

 7 mm.; span of wings 16 mm. ; female 11 mm.; span of wings 

 24 mm. 



I have not worked out the life-history of this species, but Judeich 

 and Nitsche say there is a double generation, the flies appearing in 

 May and August. It is very probable that this may be so in the 

 south of England, while in the north of Scotland there may 

 be only one generation a -year. It is not very common in 

 Northumberland. 



Fig. 174. Larvae of Croesus septen- 

 trionalis on alder. 



