Oak Gall Wasps

Here are two examples of galls made by wasp-parasites of the oak tree.  The adult females oviposit (lay eggs) in the soft stem-tissues of the oak tree.  An allergic reaction occurs and a pulpy growth with a hard outer shell becomes an incubator for the egg and then a source of food for the hatched larva.  After the larva pupates, and then hatches as an adult, it will burrow its way out to find a mate.  The two galls pictured below were harvested from the same tree, which was covered maybe with hundreds of other similar galls.  I suspect that two different kinds of wasps account for the different galls, although I have only seen living larvae in the middle of the smaller version.