National Geographic : 1989 Jun
NE OF THE FIRST to invade an acorn, the filbert worm moth pre sents a fierce vis age when seen 40 times life-size. No one knows the purpose of the tiny eye just above the large compound eye. After a filbert worm gnaws its way inside an acorn, it begins to feed. If it consumes a small acorn, it may move to others in the cluster. After metamorpho sis, the moth begins the cycle again, laying an egg on an acorn, a filbert, or another nut. Like others that take up residence in the acorn, filbert worms are vulnerable to special ized parasites. A braconid wasp will lay her own egg inside that of a filbert worm moth. As the host caterpillar hatches and de velops, the wasp larva grows within it, eventually destroying the filbert worm by bursting from its body like a nightmare monster. The tachinid fly operates in similar fashion. Round holes created by acorn weevil larvae and filbert worms often serve as entryways for other animals unable to breach the shell themselves. Called second ary colonists because they usual ly follow a first strike, such creatures also penetrate un touched acorns that are broken or sprouted. The short-snouted weevil, for example, hunts for openings, where it then feeds or lays eggs. When startled, it rolls over and plays dead. Some sap beetles can detect damaged acorns from a dis tance, often swarming in and quickly destroying them. Al though partial to tender acorn sprouts, sap beetles unleash their large appetites on a variety of plants. The one pictured even briefly gnawed at a spider's egg case inside an acorn. As acorns die, more animals move in among remains of for mer inhabitants. Breaking open a large acorn, I find a milli pede eating detritus near pale galls (foldout, left). Holes in the galls indicate that gall wasp lar vae have matured and adult wasps have left the acorn. A new species of eulophid wasp surprised me by emerging from a similar gall. Apparently it is a parasite of the gall wasp larva. At the other end of the shell, green fungus grows into the de caying meat. Hidden in crev ices, minute springtails and maggots feed on both. I also find refuse of a weevil grub, a moth pupal skin, and broken snail shells-clues to the lives of a series of inhabitants that made up the history of this acorn.