"But where is she then? I can't—Yes I can too," cries Mary in great triumph. "Here she is at one end of the egg cushion. She is a part of it."
"Well, no, not exactly," I have to say. "It is part of her, or rather she spins the cushion, which is really a sac or soft box of white wax, in which to lay her eggs. Something the way the spiders do, you know. Only their egg box is made of silk and usually fastened to a fence rail or on the bark of a tree and left there. But some of the spiders, the large, swiftly running, black kinds that live under stones, carry the silken ball with the eggs inside about with them, fastened to the end of the body. Well, this cottony cushion scale insect—that's its right name—keeps its waxen sac of eggs fastened to it, but as the egg sac is much larger than the insect itself, it can't run about any more, but has to stay for all the rest of the time until it dies in the spot where it makes the sac. However, as it gets all the food it wants by sticking its slender little beak into the broom or other plant it is on and sucking up the fresh sap, it gets on very well."
"But what makes some of the egg cushions—how pretty they are, too!—so torn and pulled open," asks Mary, who has listened to my long speech very nicely. She often gets impatient when I lecture for too many minutes together.
"That is for you to find out," I say. "There is a dreadful thing going on here if you can only see it. But a rather good thing too. Good for the broom bushes anyway, and as they are my broom bushes and I like their flowers, good for me."
Just then a very stubby, round-backed, quick little red beetle with black spots walked off a broom stem on to Mary's hand. She didn't scream, of course, nor even jerk her hand away. She may learn when she is older to be frightened when pretty, harmless, little lady-bird beetles walk on her. But now she likes all sorts of small animals, and is not afraid at all.
Mary is not at all slow to understand things, and when this hard-bodied little beetle, with a body like half a red-and-black pill, walked off the broom on to her hand, she guessed that he might have something to do with the torn-up egg cushions. So it didn't take her long to find another little beast like him actually nosing about in an egg sac and voraciously snapping up all the unfortunate tiny, red, black-legged baby scale insects. He ate the eggs, too, and seemed to take some bites at the mother insect herself, and then Mary found more of the lady-bird beetles, and still more. They were on all the broom bushes where the white cushions were. And so one of the dreadful tragedies going on in my garden was soon quite plain to Mary, and she was very sorry for the helpless white insects.
"Where did the red beetles come from?" she asked pretty soon.
"From Australia," I answered. "Or rather their great-great-grandparents did. These particular beetles were probably born right here in the garden, because a colony of them live here. But they couldn't if there were not some cottony cushion scale insects here too. For this particular kind of lady-bird beetle can't live on any other food—at least they don't—except this particular kind of scale insect and its eggs, which is surely a curious thing, isn't it?"
But Mary is so used to finding that the insects have extremely unusual and curious habits—that is, habits different from ours—that she doesn't get excited any more when I tell her about them. She does though when she finds them out for herself, which makes me wonder if I haven't wasted a good deal of time in my life giving lectures to students about things instead of always making them find out for themselves. And maybe I am wasting some more time now while I am writing!
"How did they come from Australia?" asks Mary. For she knows that Australia is several thousand miles away across the ocean from California, and lady-bird beetles do not swim. At least not from Australia to America. So I have to give Mary another informing lecture, and this is it: