Obsenmtion? on Insects affect incj the Tarnip Crojys. G5 



or the Aphis -lions^ and, being- very expert, they cause greater 

 havoc amongst the plant-Uce than probably any of those ah'eady 

 recorded. The parent flies are so numerous, as to be in a great 

 measure the cause, I beheve, of the incessant vibration of the air 

 or buzzing which we hear in the country in fine, still, sunny days 

 in the summer and autumn months: they belong to an Order 

 called DiPTERA and to the Family Syrphtd^., which is divided 

 into several Genera, and amongst them are Sc.eva''' and Chei- 

 LOSiA, containing upwards of fifty species if the larvae of these 

 are found during the spring, summ.er, and autumn in company 

 with those of the lady-birds : they are fat, fleshy maggots, some- 

 times green, at others yellow, variegated with orange ; and their 

 skins are so delicate, that the circulation of the fluids and the 

 colour of the intestines are distincdy visible even to the naked 

 eye. When the maggots first emerge from the e^^, they are 

 little inoffensive-looking creatures, scarcely visible, surrounded as 

 they are by the indolent, helpless Aphides, with their bleached, 

 cast-off skins scattered over the leaves ; but as soon as their appe- 

 tites call them into action, they thrust out their heads and necks 

 like leeches, fasten upon the nearest Aphis, and holding it up in 

 the air (fig. 23), they suck out the contents of their victim wdth 

 evident satisfaction. In this way one hungry maggot will devour 

 a hundred Aphides in an hour : when satiated, he draws himself 

 up, and lying close to the leaf, he enjoys his repose. Having 

 grown to his full size, he attaches his tail to a leaf, tree, wall, or 

 other object, and becomes a horny pupa in his own indurated 

 skin, which assumes the shape of a pear, of a dull colour (fig. 24). 

 Amongst the parent flies the most conspicuous are ScfEva Pyrastri, 

 S. Rihesii, S. hcdteata, and Ctie'dosia scripta, which I will cha- 

 racterise. 



19. S. Pyrastri, Linn. (fig. 25) is a large fly with two little 

 black horns in front of its ochreous face, and two large copper- 

 coloured eyes, nearly covering the whole head in the males, but 

 not meeting on the crown in the females ; the trunk and a lobe 

 behind called the scutal are bottle-green, densely clothed with 

 short, pale, velvety hairs ; the body is similarly clothed, flat, of a 

 good size and oval, deep black, with three long, yellowish spots 

 on each side, curved, and nearly meeting on the back ; the two 

 last segments are edged with the same colour : it has only two 

 wino-s, which are as clear as Mass, but iridescent, with several fine 

 brown nervures, forming long cells; just below their base, on 

 each side, is a little clubbed process, of an ochraceous colour, 

 called a poiser ; the six legs are pale rust-colour, the thighs black 



* Curtis's Brit. Ent. fob and pi. 509. 

 t Curtis's Guide Genera, 1240 and 1241. 

 VOL. ITT. F 



