Another Interesting Oak Gall: the Roly-Poly

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One of the most unusual galls found on oaks is the light green, sometimes speckled, ball-like Roly-Poly Galls produced under the direction of the gall wasp, Dryocosmus quercuspalustris (family Cynipidae).  The specific epithet reveals one of the most common hosts of this gall-making wasp:  Quercus palustris is the scientific name for Swamp Spanish Oak (a.k.a. Pin Oak) with palustris being Latin for “swampy” or “marshy.”

 

Roly-Poly Gall

 

However, the gall-wasp has a much wider gall-making palette including many members of the red oak group.  The galls may also be found rising from both leaves and catkins.  This is a bit unusual for gall-making arthropods with most targeting specific plant structures.

 

Roly-Poly Gall

 

The hollow galls are around 1/2" in diameter.  The “roly-poly” name comes from the unattached, white, seed-like structure that rolls around inside the galls.  The structure houses a single wasp larva.  I like to imagine newly emerging wasps staggering around after spending time rolling around inside the galls.  Probably not true, but it's an entertaining thought.

 

Roly-Poly Gall

 

Roly-Poly Gall

 

An alternate common name sometimes used for the galls is the much less descriptive Succulent Oak Gall.  Although I’ve never found a reference explaining this name, I believe it refers to the fleshy walls surrounding the roly-poly structure like the flesh of a cantaloupe.

 

Roly-Poly Gall

 

Plant galls provide both a home and food for the developing gall-maker.  But they don’t always protect the developing wasp as illustrated by the images below.  When I saw the hole in the succulent gall-wall, I thought it was an adult emergence hole.  However, cutting the gall open revealed a concavity around the hole.  A reasonable interpretation is the wasp larva became a bird meat snack; a fate not shared by its neighbor.

 

Roly-Poly Gall

 

Roly-Poly Gall

 

Roly-Poly Gall