76 : The Economy of Nature. [ ZOE 
This enemy of the enemy is the friend of the cultivated species, 
and as such our own, because in agriculture as in politics and war- 
fare, the enemy of the enemy is an ally. 
Some forty years ago financial considerations had gradually in- 
fluenced forest culture in northern Germany in such a way that a 
predominance of coniferous plantations had developed. The con- 
sequence was an increase of such insects as feed on the pine and 
spruce. These insect pests developed to such a degree that great 
damage was done by the destruction of entire forests, and for a con- 
siderable time all remedies proved futile in the afflicted districts. 
The first enemy of the enemy was the bird. ’ Insectivorous birds 
soon took care of those insect larve not covered with hair, nor 
having a disagreeable smell indicating some poisonous substance. 
So the naked caterpillars of Sphinx Pinastri and Trachea Piniperda 
were speedily reduced to a proportion no more interfering with the 
harmony in nature, but the hairy ones of Gastropacha Pini and the 
Tenthredo \arve full of irritating substance, remained almost unmo- 
lested, as the only European bird feeding on hairy caterpillars is 
- the cuckoo. 
But then a gradual increase of two classes of insects took place, 
the carnivorous and the parasite. The carnivorous was chiefly rep- 
resented by the beautiful rainbow-colored Calosoma Sycophanta, 
the parasite first by the ubiquitous 7achina, afterwards by whole 
hosts of minute parasitic wasps, of the Ichneumon and Ophion 
tribes, that laid their eggs on the injurious larvee, and the maggot 
developing devoured the insect pest from inside. The sick and 
dying larvee offering a wide field for the dissemination of vegetable 
parasites, different fungi, especially those of the Saprolegnia and 
_Torrubia types, spread from the sick to the healthy and destroyed 
whole annual generations by epidemics. 
Here is seen clearly the means applied by nature to restore the 
disturbed balance of power. Nevertheless it must be cohfessed that 
nature did not do the work quite alone. It is true that the com- 
bined efforts of whole communities, collecting the caterpillars, 
throwing them into ditches and destroying them by fire, did but 
little good and considerable evil, because it disturbed the insect- 
feeding birds. The system was also soon abandoned. But laws 
passed for the protection of insect-feeding birds took good effect, 
and finally the gradual change in the system of forest culture, by 
