Rough Bulletgalls

Galls with a house fly, Musca domestica

I have been dissecting these rough bulletgalls which were clustered all over the branches of a small bur oak at Wonders of Wildlife.  Courtney Reece who teaches at the WOLF School had noticed wasps and flies swarming the tree and sent me the whole story.  She also researched it and came up with a diagnosis of rough bulletgalls.  These galls are produced by a rough bulletgall wasp, Disholcaspis quercusmamma.

She warned me that there was a large number of yellow jacket wasps on the tree.  The numbers were down by the time I arrived but the wasps were on their sugar high and paid no attention to me.  While they are notorious for attacking people threatening them by walking over the hole of their nests in the ground or running a mower over them, these didn't seem to be bothered by my camera a few inches away. 

So why all the insect traffic?  These galls exude a sugary juice that is an invitation to party to a number of sweet-loving insects.  According to Bugwood, "Rough bulletgall wasps produce a woody, generally rounded gall on bur oak, with a slight point. Very heavy infestations can occur that largely cover twigs, reducing growth rate of the tree. The galls also exude a honeydew-like sweet material that is attractive to bees and wasps and fosters growth of sooty molds."

Bulletgall wasp - Whitney Cranshaw - CSU

D. quercusmamma has an interesting life history. 

"Females emerge in late October and early November, after a hard frost. (A small circular hole in the gall indicates emergence.) Eggs apparently are laid in the terminal growth during the fall. winged and wingless forms are produced; males apparently are unknown.

Gall opened

In late spring, the developing insect stimulates a pocket of stem tissue to produce a large rounded gall, in which the young wasp develops. Galls are pale brown and soft in early stages, later darkening and hardening. Only a single wasp develops in each gall, although sometimes other insects (inquilines) also share the gall. The larva pupates within a small cell in the center of the gall, emerging in early fall. There is one generation per season." Bugwood Wiki

Three layers surround pupa case

Pupa, case and umbilical connection

The gall is firm and leathery, hard to cut open.  The outer layer is woody and tough, covering a thick middle layer the consistency of a dry apple that breaks off in chunks.  A thin third layer surrounds the pupa case leaving an open space around it.  The case its self connects to the inner layer of the gall with a knobby stem, somewhat like an umbilical cord which provided nutrition to the larva.

Syncophila sp. parasitoid wasp - Tom Murray

In attempting to raise the gall wasp, you can't just assume that what emerges is the cause of the gall.  Like Forest Gump's box of chocolates, the life and food web doesn't end there.  There are at least five Sycophila sp.  of parasitoid wasps that  live in D. quercusmamma larvae. Sometimes other insects (inquilines) also share the gall.
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More on bulletgalls in general is at this Ohio State University site.
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Addendum:

A sharp eyed WOLF Student examining the galls noticed a tiny 1/2" patch of eggs on a leaf.  We kept the leaf in the box to see what would emerge.  There were tiny 1mm black dots in the box 3 days later.  The best macroscopic photograph I could manage showed enough in profile to call it a "ladybug" (beetle actually) larva.

H. axyridis

It is most likely a European lady beetle, Harmonia axyridis.  It is now commonly found in gardens and fields, especially where humans influence the landscape.  This isn't a bad or invasive species although it does tend to out compete with some of our native species.

H. axyridis larva

H. axyridis pupa