122 ANIMAL LIFE 
cushion scales and kept them in check. Some of these 
lady-birds (Vedalia cardinalis) were brought to California 
and released in a scale-infested orchard. The lady-birds, 
having plenty of food, thrived and produced many young. 
Soon the lady-birds were in such numbers that numbers of 
them could be distributed to other orchards. In two or 
three years the Vedalias had become so numerous and 
widely distributed that the cottony cushion scales began to 
diminish perceptibly, and soon the pest was nearly wiped 
out. But with the disappearance of the scales came also a 
disappearance of the lady-birds, and it was then discovered 
that the Vedalias fed only on cottony cushion scales and 
could not live where the scales were not. So now, in order 
to have a stock of Vedalias on hand in California it is neces- 
sary to keep protected some colonies of the cottony cushion 
scale to serve as food. Of course, with the disappearance 
of the predaceous lady-birds the scale began to increase 
again in various parts of the State, but with the sending of 
Vedalias to these localities the scale was again crushed. 
How close is the interdependence of these two species ! 
Similar relations can be traced in every group of ani- 
mals. When the salmon cease to run in the Sacramento 
River in California the otter which feeds on them takes, it 
is said, to robbing the poultry-yards; and the bear, which 
also feeds on fish, strikes out for other game, taking fruit 
or chickens or bee-hives, whatever he may find. 
