170 THE ENTOMOLOGIST. 



seem to have almost forsaken the native vegetation in favour of 

 cabbages, broccoli, and many other garden productions. 



Fortunately, there are several insects which accompany the 

 Aphis in its migrations, and destroy it in immense numbers, a 

 small brown ichneumon (probably an Aphidius) being the most 

 serviceable in this respect. These little insects may be found 

 abundantly wherever Aphides occur ; and it is not infrequent to 

 see them on window-panes indoors. The female deposits an egg 

 in the Aphis by means of a long ovipositor with which she is 

 furnished. From this a minute grub proceeds, which devours 

 the internal portions of the Aphis, reducing it at last to an oval 

 shell, fixed firmly to a leaf, by its edges. When in this condition 

 the Aphis is of course quite dead, and the ichneumon is probably 

 in the pupa state, as the emergence of the perfect insect takes 

 place in a few days. Numbers of these exuviae may be found in 

 most of the communities, and I have frequently seen large ones 

 nearly exterminated by this insect alone. 



The larvae of the genus Syrphus, among the Diptera, are well 

 known to be great Aphis consumers ; and as these insects are 

 here very abundant it is not surprising to find the larvae plentiful 

 in the Aphis colonies. The species which I have noticed most 

 commonly is Syrphus ortas, but I expect the others have a very 

 similar economy. The larva of this insect when full grown 

 measures about 5 lines in length ; its surface is so much wrinkled 

 that the divisions of the various segments are not distinguishable; 

 the abdomen and sides are dark green, the back being of a yellowish 

 brown colour, which is caused by the presence of a large quantity 

 of fatty substance situated just beneath the thin skin of the insect. 

 In the middle of this yellowish portion is a broad dark green line, 

 extending from within a short distance of each end of the larva. 

 This is the dorsal vessel, and by careful examination its pulsations 

 may be distinctly detected. Near the anal extremity, on the 

 dorsal surface of the larva, is a short thick tube, which has at its 

 apex what appear to be four lunate spiracular holes. I could not 

 detect the opening and closing of these, although I watched care- 

 fully, so cannot be quite certain as to their function. The anal 

 aperture lays exactly opposite this tube on the ventral surface of 

 the body. These larvae grow very slowly, probably occupying 

 several weeks to attain full growth. They eat large quantities of 

 Aphides, which they have a very peculiar method of procuring, 



