There are other enemies, too, of the oak-house dwellers. Birds like to peck into the soft, growing galls to get at the tidbits inside. And predaceous beetles and other strong-jawed insects with a fondness for helpless, soft-bodied, juicy grubs would like to gnaw into the houses. So the houses have to protect the dwellers inside, and they do this in various ways. Some are extra thick-walled or have an extra-hard outer shell. Some are covered with spines or hairs. Some have a viscous gluey excretion, some have a very bad odor, some are so colored and patterned that they are very hard to distinguish from the foliage or from the fallen leaves around them, and, finally, some secrete a sweetish honey-dew which attracts ants, and these fierce visitors, who are content with the honey-dew, probably drive away many visiting parasites and predaceous insects. But it would be tiresome to go on and tell you all the things we are finding out about the houses of oak and the insects that live in them. Of how we have got them to lay their eggs right before our eyes on little fresh branches that we bring into the house. Of how the houses begin to form under the bark or leaf surface as mere little swellings and then break through and get larger and larger and take on their characteristic form and color. Of how we have to study the gall-dwellers with a microscope, for the largest that we have found yet--the ones that make the big galls shown in Sekko's picture--are only one-fifth of an inch long, while others are not more than one-twenty-fifth of an inch long. Of how some kinds have to lay their eggs always on the same kind of oak-tree, while others prick different kinds of oaks. Nor can we tell of the questions and problems that we are trying to answer. As why it is that two galls made by two different kinds of gall-insects, but in the same parts, as leaves, of the same oak-tree, should be so different, or why the galls in different kinds of trees, though made by the same kind of insect, should be alike, as they usually are. And why with some kinds of the house-dwellers the children grow up to be different from the mother, but their own children grow up like the grandmother, and different from themselves. Or how they know not to lay too many eggs in one place, the ones making little galls often laying several to many eggs in one leaf, but the ones making large galls being careful to lay only one egg in a leaf. And a lot of other things that they do that need explaining.