THE POPULATION OF AN OLD APPLE TREE 303 
in the orchard at almost any time; and by carefully watch- 
ing, may see them chiseling holes with their stout beaks, 
and extracting borers from the wood, or caterpillars hidden 
under the heavy flakes of bark. Their perforations may be 
found on any old tree, especially in bark and dead bough. 
Often there are sap-pits to be seen, also, in the fresh green 
bark of the larger boughs. These are placed in regular trans- 
verse rows, Close together. They are made by sapsuckers, 
at the time of sap-flow in the early spring (see Chapter 22, 
page 169). These are made to “bleed” the tree and not to 
rid it of pests. They are not very harmful, however, for they 
are made in such a way that they quickly heal in the grow- 
ing season. ‘The pits are small, and living bark from which 
new growth may spread is left between the pits. Nature 
has taught the sapsuckers how to take the sap and soft fiber 
of the inner bark from the trees without seriously injuring 
them. The sapsuckers pay for this by eating injurious 
insects that hide beneath the old and flaky bark of the trunks. 
A few birds are residents in the trees, but many others 
come and go. Some, like crows and jays, slip in unawares, 
merely to peck holes in the reddest of the apples on the 
upper boughs. Others, like cuckoos, come to feed on cater- 
pillars. There are many mammals that like apples as well 
as we do; and some small wild ones make nocturnal visits to 
the orchard. There are many insects that visit it, in blos- 
soming time, for nectar or for pollen, as we have seen in 
Study 30. But the most important part of the population 
of the apple tree is the resident population, composed of 
insects that are wholly dependent on the apple tree for their 
livelihood. 
These are both beneficial and injuriousinsects; and the latter 
will usually appear to be in excess. There is no part of the 
tree exempt from the attacks of some of them. On the 
roots, there are wooly aphids clustering and causing rounded 
