Will thousands of oak leaf galls produce a mass invasion of wasps?

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DEAR JOAN: There has been much discussion on Nextdoor about oak galls lately, mostly about how the galls are harmless to the tree and that they’re quite prevalent this year on oak trees around Pleasant Hill, Lafayette, Martinez and Walnut Creek.

I can attest that I sweep up literally millions every week from my yard; it’s never been anywhere near this intense in years past.

Does this mean that we will be swarmed by wasps in the spring? I’ve always had a few wasps, even found a few nests, but will the wasp invasion next spring rival the locust swarms of the Bible? Will we be able to venture outside at all?

Liz Fisher, Pleasant Hill

DEAR LIZ: No need to buy protective clothing or barricade yourself indoors. The wasps that emerge from the galls are tiny, non-aggressive and live very short lives.

When most people hear the word “wasp,” they immediately conjure images of yellow jackets and hornets. But yellow jackets and gall wasps are very different. For one thing, they belong to different families. Yellow jackets are in the Vespidae family and gall wasps belong to the friendlier Cynipidae family.

The two most common are the oak apple galls, produced by Andricus californicus wasps, and the red cap galls, which look like tiny red Hershey’s kisses, produced by Andricus kingi.

I said the wasp produces the galls, but in reality, it’s the oak that produces them. Here’s what happens: One of these very small wasps bores a tiny hole in the tree bark or, more commonly, in a leaf or leaf bud. The wasp lays an egg inside and injects a chemical that starts the process. The egg then takes over, secreting hormones that hijack the gall’s genetic system and trick the oak into forming a gall. The egg is encapsulated by the gall chamber as the hard, outer surface forms.

When the larva is almost to maturity, it starts eating the inside of its home. It will then drill a tiny escape hole, emerging as an adult. Once on the outside, the cycle begins again, with wasps quickly laying eggs for the next generation before dying.

We are seeing a lot of red caps this year, probably brought on by the milder weather. Galls form both in the spring and autumn.

Staci Hobbet, a natural history docent for Mount Diablo State

Source:: The Mercury News – Lifestyle

      

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