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Adleria quercusstrobilana - Andricus quercusstrobilanus

Adleria quercusstrobilana - Andricus quercusstrobilanus
Hillside along a village street., Cook County, Illinois, USA
September 9, 2008
Growing about eye level on the twig of a small Swamp White Oak, Quercus bicolor. More galls were noted higher up in another nearby tree of about the same size. The texture of the galls is leathery, but firm.

Images of this individual: tag all
Adleria quercusstrobilana - Andricus quercusstrobilanus Adleria quercusstrobilana - Andricus quercusstrobilanus Adleria quercusstrobilana - Andricus quercusstrobilanus

Some observations:
This oak gall was first observed on September 9, 2008. Subsequent visits has revealed that there are at least 20 clusters of various sizes on at least half of the 10 Swamp White Oaks(8-15 feet tall) in this area. The shape of the cluster is generally orbital but there are veriations depending on the number of eggs that were laid and have developed. This particular gall cluster(pictured above) was formed by two groups of eggs being laid on opposite sides of the stem about a centimeter apart. The galls very in color but while growing are a mix of yellow, pink and red. At the end of their growth the change color loosing the pink and red with some becoming mostly yellow before turning brown.

After turning brown the galls start to fall from the cluster to the ground. At one point there were a large number of galls under the trees, but during later visits their numbers have decreased drastically. Two galls have been found that were chewed open. From the markings on the galls it would appear to have been caused by squirrels.

Some additional photos have been added, showing the different stages of the galls development.

oak gall
Very pretty galls! Also fairly distinctive. Based on a combination of Felt 1940 (1), Weld 1959 (2), and various internet references, this is Adleria quercusstrobilana. Weld lists the species as Adleria strobilana and Felt lists the species as Cynips strobilana. Nearctica lists the species as Adleria quercusstrobilana so I'm going with that name.

Most of the internet references are from very old texts and use Cynips. The galls are greenish or rose-colored when young and turn brown with age. They occur on Quercus bicolor, macrocarpa, and lyrata.

Here is the only photo I found online, of an older gall, part of a slide show so you have to look for it.

Here are some other rather old and incomplete internet references (search for "strobilana" if you don't see the reference immediately): 1, 2, 3. The AMNH Bulletin from 1893 says that the gall is induced by "the sting of the insect on the single leaves of a bud" but actually cynipid galls start growing after the eggs from a female hatch -- she is not "stinging" but laying eggs, and the galls don't start growing until after the eggs hatch.

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