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November 2018 Natural Mystery Answered

posted Dec 4, 2018, 2:27 PM by Jonathan Poppele   [ updated Dec 4, 2018, 2:28 PM ]
Our November Natural Mystery was a two-part question. We were looking for both for what this is and the tree that it grew on. Though these appear at first glance to be the seed-bearing cones of a conifer, they actually come from one of our local deciduous trees. Several of you recognized both the tree and the cause of this distinct pinecone-like growth. Here is an excellent explanation that came in from one naturalist, who wished to remain anonymous:

"This is a willow pinecone gall caused by a gall midge (Rabdophaga spp.) infecting a willow tree (Salix spp.)

Galls are growths on plant species resulting from, among other things, certain insect larvae.  An adult gall-making insect such as a wasp, midge, or moth, has evolved to lay its eggs on or in plant tissue.  The larvae that hatch from these eggs burrow or chew, which stimulates the plant to create an abnormal growth in that area, inside which the insect larvae take shelter and feed.  Each gall-making insect species is specific to a plant species or genus.

These look a lot like hemlock cones, given their size and the shape of their scales, but eastern hemlock cones are a little longer for the width and don't have the taper at the end.  Also, the more 'open' gall on the right is not how any cone from a conifer looks, with the scales giving way to the more narrow, open structures at the end.

To answer this question, I used some general knowledge of galls in general and willow galls in particular from a college entomology class.  I confirmed my ID and description using Tracks and Sign of Insects and Other Invertebrates by Noah Charney and Charley Eiseman."

Congratulations to Joe Plantenberg, Kirsten Welge, and two anonymous naturalists who correctly identified this sign.