HYMENOPTEHA — SAW-FLIES, ETC. 



185 



Crcesus septentkionalis, Leach (Cameioii). 

 Nematus septentrionalU, L. 



This species is said to be very common in some parts of tlie country ; 

 and Cameron says the larvae feed on poplar, aspen, birch, willows, 

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

 of these plants, but 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 be 

 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 

 as large as the body. Wings 

 hyaline. Spread of wings 16 

 mm. in male and 21 mm. in 

 female. 



The larvfe (fig. I7r) 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 Fig. 174.— larnro/cnpsusseiiteu- 



1 - /. tiionalis on alder. 



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, as I 

 have just found that larvae collected at Catcleugh, Northumberland, 

 on September 23, 1910, hatched out on May 31, 1911. It is not 

 very common in Northumberland. 



