108 



KNOWLEDGE. 



[May 1, 1897. 



galls are so plentiful the perfect insects are very scarce. I 

 have never yet bred a specimen of the male. At birth the 

 larva is quite white, but in the course of a few weeks be- 

 comes a delicate apple-green, the head large and rounded, 

 having a few dark markings at the sides — the body much 



Fig. 7. — Section of Gall, showing Paralyzed Larva and Egg 

 of Parasite. 



wrinkled, the anal segments curved down and rounded 

 {see Fig. 4). When full fed the larva is a quarter of an 

 inch long, and such as have managed to escape the attacks 

 of innumerable parasites and predaceous insects eat their 

 way out through the channel on the under side, crawl 

 down the leaf stem and branch, or not unfrequently tumble 

 down to the ground, in which they spin a small brown- 

 coloured cocoon. Others crawl down the trunk, and, if 

 possible, spin their cocoon at the back of some loose bark, 

 where frequently many of the cocoons can be found clus- 

 tered together. These are easily collected, and in due 

 time saw-flies and various parasites are bred. The latter 

 are more numerous. The first broods of saw-flies emerge 

 in April and May, the second in the latter part of 

 autumn, when the wiUow is throwing out a second growth 

 of terminal leaves. 



A lifetime would hardly be long enough in which to study 

 and write out the life-histories of the various insects which 

 I noticed frequented the willows in my little back garden, 

 but one or two of the parasites of the willow saw-fly may 

 be noted. One whose identity I have not yet decided is, 

 perhaps, one of the most interesting. I first observed this 

 beautiful parasite flying around the willow leaves during 

 the first week in June, but on capturing one I noticed that 

 it had a most i^ecuhar " curly tail " — or, rather, the sheaths 

 of the ovipositor were curved in almost a semicircle — and 

 how this could be brought down on to a semicircular gall 



Fia. 8. — Section of Gall, showing Paralyzed Larva and Egg 

 and Larva of Parasite. 



of 



I could not at first understand, but after a number 

 days' observation everything was made perfectly clear. 



All Hymenojitera love bright sunshine, and that is the 

 only time when saw-flies and parasites are at work. The 

 first are very wary. I found it best to take my stand 

 close to the tree before the sun shone, as any approach was 



detected at once. In this way I was enabled to observe 

 every movement. 



The parasite (Fig. 5) is a small insect a quarter of an 

 inch in length, the male clouded with red and black, 

 whereas the female has no bright colouring. The male 

 always follows the female, most persistently and successfully 

 threading its way between branches and leaves, its sight 

 being simply marvellous. As soon as the honeymoon is 

 over the female quietly hovers around the terminals, and, 

 settling upon a gall-covered leaf, rapidly sounds the first 

 gall. If it contains an occupant, the parasite quickly 

 mounts on to the upper surface of the crimson gall, and in 

 a moment — not longer — her abdomen, with the exquisitely- 

 formed waist, is bent down between the third pair of legs, 

 which absolutely take hold of the sheaths of the ovipositor 

 — the peculiarly-formed hairs on the coxfe holding the 

 long and delicate auger-like organ between them, until the 

 barbed points are pressed into the gall (Fig. G), when 

 immediately the sheaths and abdomen move back into 

 their original position. By muscular effort the long setffi 

 are driven through the walls of the gall, and right into the 

 body of the larva of the saw-fly, and, after the parasite has 

 repeatedly stabbed and injected small drops of formic acid 

 into it, this long auger is withdrawn, and the poor larva 



Eia. a- 



-Section of Gall, showing Skin of Larva and Pupa 

 of Parasite. 



lies paralyzed. After the parasite has replaced its organ 

 between the sheaths, it turns and twists about in a very 

 comical manner for a few moments, then it crawls round 

 to the under side of the gall and inserts its ovipositor. At 

 first my excitement prevented me from discovering its 

 purpose, for, in my endeavour to focus my magnifier, I 

 disturbed the parasite, which flew away, as did several 

 others from the same cause. However, I carefully cut 

 open the galls through which the parasite had driven its 

 setie, and found that the lovely apple-green larva had 

 changed to a sickly yellow colour — all its activity was 

 gone, and only a slight movement visible. 



After repeated failure, I after all managed to watch a 

 parasite insert its ovipositor in the channel on the under 

 side of the gall ; the antennte were closely enibracmg the 

 gall, and from their tremulous motion I concluded an egg 

 was being laid. A few minutes more, and the parasite 

 resumed its activity. The antennte were held aloof, and 

 the creature seemed to be " clucking," though in a note 

 which did not reach my hearing. When this was over, 

 away it flew. I quickly, but very carefully, cut the gall 

 down the centre without removing the leaf, and there, on 

 applying the magnifier, I saw the egg (Fig. 7) lying in 

 the channel, an eighth of an inch away from the paralyzed 



