Chris Barnhart sent me these pictures with a question. "When I saw all these twigs down under my neighbors' red oak tree, I thought twig girdlers were at work. But it looks more like squirrels cut them, and that they are chewing up some kind of woody galls."
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| Gouty oak galls along Bull Creek - REK |
The multiple channels in Chris's opened gall are typical of gouty oak galls. They are discussed at length in this Missouri University link. They have a complex life cycle beginning when tiny stinger-less Cynipid wasps which lay their eggs on the oak leaf buds in the early spring and form tiny galls. The adults that emerge from these galls in a few months mate and lay more eggs, this time on newly forming tree shoots. This time the galls develop over several years, eventually girdling the stem. These are the galls that Chris is holding.
I came across several sources that describe squirrels attacking these galls. In addition to the Missouri Botanical Garden, there was a story on St. Louis Public Radio about an outbreak of chewed galls raining down on lawns. Like the sawflies and other pests, these are primarily a problem in suburban areas where they congregate in a few isolated trees. I have seen these yearly for 20 years but never in numbers to be anything more than an interesting part of nature.