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There are many types of gall and each one is distinct and caused by a different vector. Some are caused by insects including Aphids and, Wasps. Others are caused by Mites. Still others are caused by Fungi or Rust. This particular gall is the Oak Apple Gall which is caused by an insect. The adult, probably a Gall Wasp, lays an egg in a leaf and the chemicals start to change the leaf to form the gall. As the gall grows, the insect larva eats the threads inside of the gall until it is hollow and then the insect pupates. When the adult emerges, probably in the spring, it finds another adult and mates and then the female of the pair looks for the type of leaf it wants and lays an egg on each selected leaf, starting the cycle over. This gall is recently formed and probably blew off before the egg hatched. Galls are mostly cosmetic and don't usually harm the host plant. Those formed by insects are probably a good source of food to insect eating birds.
Posted by joem50 on 2010-05-14, 11:12:22 Report this as offensive.
Oak Apple Gall Wasp (Amphibolips confluenta)
Posted by hortensial on 2010-07-14, 14:30:53 Report this as offensive.
Marble gall perhaps? Found on the ground in Cleveland, Ohio. (Golf ball for size comparison)
Uploaded by fuzychiapet
on 2010-05-09, 15:01:03 into Garden Junk, Name That Plant