I found these beautiful galls in my yard this weekend, while doing yard work:
It’s likely woolly catkin gall, made by a wasp: Callirhytis quercusoperator (Osten Sacken, 1862) (Cynipidae). We’ve started another large project here at the Frost, but I’ll have to wait until it’s official before providing more details here. It involves galls, though, and we are now scaling up our collecting efforts dramatically. These little galls are are the first of many!
Callirhytis quercusoperator is an interesting species, and I am excited and intrigued to find this species in my yard. Like many gall wasps, this one has two generations per year, one sexual and one asexual. The sexual generation induces the galls you see above, on catkins of many Quercus species. The larvae grow quickly in these galls, which soon fall to the forest floor. The asexual generation emerges there, flies to the canopy, and seeks out young acorns, just getting started on the trees above. The asexual females lay their eggs just inside the growing acorn cap and induce another gall – the acorn pip gall. Hopefully I will find those all over my yard later in the summer and fall. They look almost like mini acorns, developing beside a normal acorn. We don’t have any acorn pip galls in our collection, and the clearest photo I could find online is this one from a slideshow Patrick Brose presented at the 2013 Schatz Colloquium:
These acorn pip galls apparently secrete a nectar-like substance that attracts ants and other insects. Even bumble bees have been observed foraging at these galls! Find out more about these galls in Felt (1940), Kinsey (1922), Bassett (1973), and by cruising around iNaturalist.