es The Economy of Nature. [ ZOE 
phenomena on desert lands and cultivated grounds consists chiefly 
in the intensity and rapidity of their development on the former, 
and their proportions are quite in keeping with the expanse of 
horizon and unrelieved monotony of the surface. 
As long as the inordinate multiplication of the species affects only 
the desert region it is of the highest biological, but of little prac- 
tical interest. Unfortunately in many instances even the immense 
extent of the desert cannot hold the swarms of suddenly accumu- 
lated beings. Like a cup filled to the brim it foams over and sends 
its myriads into distant regions to destroy and to be destroyed, be- 
cause enemies in the shape of birds follow the wandering host, and 
even in their own bodies the wanderers carry the parasitic germs 
of animal as well as fungoid destroyers. 
I have had no opportunity to study the wandering grasshoppers 
which occasionally, from southern and western deserts, are poured 
into California, and so I do not know if they are followed by a 
host of birds as are those in the Hungarian puszta, the Russian 
steppes or the Sahara. In Europe it is especially a little hawk or 
falcon, 7inmnunculus, whose swarms appear almost with the wander- 
ing pest when an hour before no bird was visible. 
The only enemy of the grasshspper whose acquaintance I have 
had an opportunity to make is a beetle of the Cantharid order, a 
Tigrodera. \ have always received a certain number of specimens 
of this useful insect during a grasshopper year, never at any 
other time, and as I am frequently consulted about insects, espec- 
ially when they are as showy as the 7zgrodera, I conclude that 
under ordinary circumstances the species is rather rare and only 
multiplies in proportion to its larva food, the grasshopper. Judging 
from analogy the larva of the 7igrodera needs several years before 
it turns to a beetle, the only stage in which I have seen it. All the 
related insects are carnivorous and parasitic on other insects, de- 
vour first eggs, then young larve, and generally in the last stage of 
their larval existence are parasitic. 
I am inclined to consider this insect also parasitic in its last lar- 
val stage, but have not yet had opportunities to collect evidence. 
I suspect that the frequent deaths occurring amongst the herds 
of turkeys that are led out against the grasshopper are not owing 
to indigestion caused by greediness of the bird, but to having 
swallowed a grasshopper infested by this parasite which contains, 
