It's fall gall season!

Next time you're out for a walk in your neighborhood or on a hike in the Bay Area, try looking closely at some of the oaks, especially Valley Oak and Blue Oak. Examine their leaves carefully, and look for little structures. Remember - oaks only grow leaves, twigs, and acorns. Everything else might be part of the incredible science mystery called -insect galls!

Galls are little structures induced by an insect (or mites, or fungus). The plant creates a little structure where the insect larva can develop and hide from most of its natural predators.

Diversity of fall oak galls

Some of the gall wasps go through two generations each year - 1) spring/ bisexual generation: a fast growing gall, with both male and female wasps inside, 2) fall/ unisexual generation: more colorful , with only females inside, that will reproduce parthenogenetically after emerging in the next spring.