INSECTS INJURIOUS IN 1902. 23 
injurious, their ability to do injury beng directly proportionate to 
their numbers, but only a few species ever become numerous 
enough to cause serious injury. 
A word about hopper-dozers may not be out of place as I have 
met a number of farmers not familiar with their construction. 
The drawing given, Fig. 16, will explain their structure al- 
most without the use of words. The material is galvanized iron. 
The pan may be 8, 12 or 16 feet long. The larger pans are divid- 
ed into compartments by soldered partitions, thus preventing the 
oil from running to one end on sloping ground and spilling. The 
back of the pan is about 4 inches high and the front is turned up 
about 3 inches. A 4 inch board is fastened.to the under side of 
the pan at each end, the broad surface acting as a runner. These 
Fig. 16.—Large opper-dozer with partitions (after Riley). 
pieces project in front and to them ropes are tied for drawing 
the machine. Early in the season one horse is used, later when 
the hoppers get more active two are used, one at each end, so that 
the insects, startled by the horses, will jump for the main part to- 
wards the center and be caught by the pan. Uprights two feet 
long at the back of the pan, not shown in figure, support a white 
cloth which serves to attract the Locusts and to prevent their fly- 
ing completely over the hopper-dozer. In this connection it may 
be said that it is economical to use but little oil. That is, if water 
to the depth of two inches say, is placed in the pan and enough 
oil poured upon that to make a thin film, it will be quite as ef- 
fective as if it were all oil. For, even if the grasshopper barely 
touches the oil and then hops out, he is sure to die. Some of the 
farmers in the Hill River district used as many as 12 or 15 gallons 
of oil daily, whereas if water had been used as above indicated, five 
