See that pink fuzzy critter in the middle of this dried oak leaf?
I thought it was some form of caterpillar cocoon. Some, nice cozy home out of which a butterfly or moth would hatch, with the fuzzy form being suitably appropriate to our Minnesota winters.
Ha! I was close, but no cigar.
This is a gall. Galls are formed by the activity of insects or mites on plants, including oak leaves, however, the galls are actually formed by the plants themselves as a reaction to “mechanical damage or salivary secretions” from the insects. According to the University of Minnesota’s Extension Service, “The gall-making organism develops inside the gall and the gall continues to grow as the insect/mite feeds and matures. Once gall formation is initiated, many galls will continue to form even if the insect dies.”
So, there could be insects inside the gall, but maybe not.
I’ve seen galls before on our oak leaves, but was never curious enough to look them up until now. Perhaps it was the preponderance of them this year that nudged me into the research.
Galls can take different forms depending on what plant they grow on and what insect forms them. Have you seen galls other than the fuzzy ones in my pictures?