St. Nicholas/Volume 32/Number 3/Nature and Science/Baby Beetle

by S. Frank Aaron

When the Branch Breaks, the Baby Beetle will Fall.

If, at almost any time of the year, we walk through the woods where the red, scarlet, black, or pin oaks are growing,—that is, where we find those that ripen their acorns in two seasons, and therefore belong in the pin-oak group,—we shall probably find on the ground fallen branches that vary in size from that of a lead-pencil to that of one’s thumb, or even larger. These, at the broken end, appear as if cut away within the wood, so that only a thin portion is left under the bark. Within the rather uneven cut, generally near the center of the growth, isa small hole tightly plugged by the “powder post” of a beetle larva. Split open the branch or twig, when a burrow will be seen, and the little white, soft, hard-jawed larva that made it will be found, or perhaps the inactive pupa, shown in Fig. 1, the illustration below. The beetle, emerging in the spring or early summer, lays its eggs on the soft twigs of the oak, cutting a slit for the purpose, and depositing a single egg on each selected twig. The tiny larva cuts its way into the soft pith until it reaches the larger branch, where it increases its burrow as it increases its size. After the branch is cat, during the autumn the larva withdraws into its burrow, and plugs up the hole at p1 (Fig. 2, see next page), so that no enemy can enter when the limb falls. It then continues to eat its way along the branch, and makes another plug (2), and is now nearly full grown. The plugs are a mixtnre of saliva and of the dust which the larva makes in its burrowing, They are nearly as hard as the wood itself. The larva is thus well protected from the treeloving woodpeckers, which seldom hunt on the ground, and never scratch among the fallen leaves for food. It becomes a pupa in the cell in front of the

Fig. 1. A branch: split open to show the enlarged papa of the oak-pruner beetle (Elaphidion villosum). The beetle is about five eighths of an inch long.

Fig. 2. Red-oak branch and twig, cut open to show the burrow of the oak-pruner larva. a, where the egg was deposited; c, where the branch was cut nearly off; p1, first powder-post plug; p2 second plug

second powder-post plug, and when the beetle is ready to come out it cuts its way through both plugs and enters the great world, where it visits other oaks of the right kind, lays its eggs on the selected twigs, and the round of development again begins.

S. Frank Aaron.