A gooey gall

It’s common to see galls on oak trees, but many of the ones on this live oak (Quercus fusiformis) had sticky drops on their surface that I’d never seen before and still don’t know how to account for. Joe Marcus of the Lady Bird Johnson Wildflower Center provided a couple of good hypotheses: “Apparently it’s an open question.  Does the host tree produce the sticky substance on the gall to capture the exiting adult wasp or perhaps to attract gall wasp parasites, or does the larval wasp cause the gall to produce the exudates to attract others of its species for reproduction?  I don’t think the question has been answered.”

Note the hole in the upper left part of the gall through which a wasp would have exited.

Today’s photograph is from an October 18th field trip to the Shield Ranch southwest of Austin.

© 2015 Steven Schwartzman