II. 



1 



Some Account of the Gall-Making Insects of 



Australia. 



THE very interesting paper on the formation of vegetal galls 

 and their inhabitants in the November number of Natural 

 Science has induced me to offer some notes of my observations on 

 the galls produced in this country, and the conclusions I have arrived 

 at as to their origin after close study extending over some years. 



The researches of many of our entomologists have shown that 

 the insect fauna of most countries is regulated by, and adapts itself 

 to, its surroundings in a most remarkable manner. Though, in so 

 large a mass of land as Australia, we have a great range of climate 

 and a diversified vegetation, the bulk of this great island is covered 

 with stunted, scrubby forest trees, broken here and there along the 

 coastal mountains and alluvial flats by thick forest lands, and in the 

 north-eastern parts by dense jungles and tropical bushes. 



One can safely say that the trees prevaiUng over nine-tenths of 

 Australia are " gum trees," Myrtaceous trees chiefly belonging to the 

 genus Eucalyptus, and smaller shrubby trees belonging to the order 

 Leguminosse, genus Acacia, commonly known under the names of 

 wattles, myal, mulga, etc. 



In the genus Eucalyptus some 140 species are described, of 

 which the extreme forms are the small, bamboo-like, slender-stemmed 

 mallee-scrub gums, growing up in clumps from a common base, with 

 thin, long, slender roots just below the surface of the dry, sandy country 

 they cover in many of the inland districts, and the giant gums of 

 Tasmania and South Gippsland, whose roots strike deep down into 

 rich alluvial soil, and whose great rounded trunks shoot up 400 feet 

 in height. 



The Australian gum trees may be considered as taking the position 

 in our forests that the oak trees occupy in those of England and 

 Europe. As, therefore, on the oaks of the Old World the larger pro- 

 portion of the most interesting galls are found, so in this country 

 the bulk of ours are produced upon Eucalypti. On the western 

 plains and uplands, but also in a less degree in the denser scrubs 

 clothing the coastal ranges, bush fires that devastate miles and miles 



