46 



THE NATURALIST. 



The Willows and their Galls. 



Before speaking of the willows 

 and the gall-flies that affect them, I 

 would remark that we have in our 

 neighbourhood three or four tolerably 

 common species. They are Salix 

 capraa, 8. fragilis, 8. fusca, and 8. 

 alba. These are all more or less 

 attacked by Dipterous and Hymenop- 

 terous gall-insects, and foremost 

 in each group are Cecidomyise and 

 Tenthredines. I will begin with 

 our Easter friend, the great round- 

 leaved Willow, or Palm, as it is called 

 in the north. (8. caprcea.) In the 

 winter and spring the uppermost 

 shoots not unfrequently terminate 

 in a tuft of withered leaves in the 

 form of a rose. If this be examined 

 more narrowly, the centre will be 

 found to consist of closely fitting 

 bracts, and in the midst of them is 

 a reddish-coloured grub. This is 

 the pupa of a gall-gnat, fCecidomyia 

 rosaria) and in this once green tuft it 

 has fed, and here it nestles till it 

 puts on wings in the month of May. 

 Examine the leaves of this same 

 willow, as also of other species, in 

 the late autumn, and you will find 

 them occasionally beset with hollow 

 blisters. Each has been the home 

 of the larva of a saw-fly. (Tenthredo.j 

 Here it has fed through the summer, 

 and when it has eaten to the full, it 

 has made its way out of the blister, 

 and bored into the soil below, to 

 await its final transformation. 



The Brittle Willow (S./m^fiZw) is 

 subject to the attacks of another 

 gall-gnat that has obtained the name 

 of Cecidomyia salicis. The economy 

 of this gnat is totally different from 

 that of the species that frequents 

 the palm. The twig is made to 

 assume the appearance of a long, 

 rounded, woody knot. In this knot 

 a whole colony of larvae are housed, 

 and find therein food and shelter, 

 till they emerge, and enter on their 

 winged existence. These contorted 

 twigs I have noticed on Salioo fusca 

 as well as 8. fragilis. The manner 

 of escape of the gnat would appear 

 to be by means of some acid solvent, 

 with which the pupa is provided. 

 I have repeatedly witnessed the exit 

 from the gall, which is effected with 

 wonderful rapidity. 



The last gall to which I would 

 draw attention occurs on Salix 

 vitcllina. It is the work of a saw-fly. 

 {Cryptocampus angustus.) The shoot 

 is grooved by the parent saw-fly, and 

 her eggs deposited therein ; the sap 

 stagnates, and a spongy matter is 

 formed over the wound. In this 

 the grubs feed in security, as many 

 as three or four being tenants of the 

 same gall, whence they emerge in 

 April, to perform the same round of 

 existence as their parents. The 

 imago I have hatched this year ; and 

 Mr. Smith, of the British Museum, 

 informs me that it is probably the 

 first time that this saw-fly has been 



