Oak Apple Gall Wasp (Amphibolips confluenta)

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Oak apple galls form when a female Amphibolips confluenta wasp injects her egg into a budding oak leaf. The tree responds by forming a gall around the insect. The gall protects the growing insect and provides it with sustenance.

I’ve seen hundreds of oak apple galls, but they’ve been old galls that were brown, dry, and papery, with a small hole where the adult wasp bored its way out. On Sunday we hiked to White Oak Sinks in the Great Smoky Mountains National Park. The fresh galls we found on the trail were green and pliable, and the wasp pupae were still growing inside.

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Above: the inside is mostly air, with a seed-like structure in the center suspended by wispy fibers.

Below: With the seed-like middle structure opened, the white wasp pupae can be seen.

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Here’s a very good natural history of Amphibolips confluenta, with pictures of the dried galls and the adult wasp.

October 25, 2006 update – Two of these pictures will be included in Oak Gallwasps of the Western Palaearctic, to be published by the Ray Society (Natural History Museum, London).

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16 Responses to Oak Apple Gall Wasp (Amphibolips confluenta)

  1. Chris Wage says:

    Galls are so bizarre. We had an infestation of these galls (i can’t remember the specific name) in the shrubs outside of our apartment.

    There are some pictures here

  2. lobbygow says:

    Beautiful!

    Keep this up and cat blogging will become so passe.

  3. Les Jones says:

    Thanks, guys.

    Chris: That’s wild. I’ve never seen those before. In picture 17, is that the critter erupting from the top of the gall?

  4. Chris Wage says:

    Yep. There was a 1-2″ larva inside each one — they almost look like Monarch butterfly larva.. I talked to an entomologist or someone at some point that told me what they were..

    They hatch from an egg inside a branch and immediately start secreting a hormone that promotes cell-growth in the surrounding plant tissue. Eventually it forms a coccoon of the live tissue that it keeps on its back, sorta like a hermit crab has a shell.

    Very weird. Then eventually, they attach to something and the cocoon seals up. I can’t remember what they turn into, though.

  5. hellbent says:

    That’s my kind of post! It might be worthwhile to point out that the gall wasp is a tiny thing that most people would mistake for a gnat, if they noticed it at all.

    Chris, your insect is a bagworm moth larva, and those are not galls, just protective cases the caterpillar builds from dead plant parts and silk it secretes from its mouthparts. The adults are nondescript medium-sized moths.

  6. Do they taste good?

    Yours,
    Wince

  7. Chris Wage says:

    Interesting.. so the plant material is just dead? How disappointing.

    Is that the definition of gall — it has to contain live tissue?

  8. hellbent says:

    Galls are formed by a live plant, typically as a reaction to chemicals injected by an insect along with an egg. Bagworm cases are constructed by the insect from plant materials. I’m not sure if they use live or dead tissues during construction, but it’s definitely dead once it’s silked to the case.

    I’m not sure where you got that stuff about hormones promoting cell growth. That sounds like how galls form, but those cases the bagworms drag around are not galls. Perhaps a bagworm uses a gall to start its case, then adds on additional plant material as it grows and needs a bigger case. I’ve never heard that, but it’s possible.

    If you know caddisflies (a/k/a “stickbait”), they build their cases the same way. Some species use twigs and bits of leaves, and some use rocks, but they all cement their case together with silk. Moths evolved from caddisflies, and some species retain the habit of dragging a case around for protection. Moths that eat wool, the ones mothballs are intended to ward off, are case-builders. If you ever get an infestation of them, you may find little tubes of lint creeping slowly across a wall with a tiny caterpillar inside. The cocoons of moths and butterflies (and wasps) are essentially these same cases constructed entirely of silk, without the interwoven bits of debris.

  9. dave says:

    I for one welcome our Oak Gall Wasp Overlords…
    cool post

  10. Chris Range says:

    One of the freakier things you’ll find on any blog that’s still Rated-G

  11. Way Cool (not Best Buy)

    Sorry for the lack of posts, but I was on travel yesterday in Charlotte, NC (a very strange place) and am trying to catch up on other things here.

    In the meantime, check out this way cool post at Les’s place or read about the Geek giving Best Buy…

  12. tony says:

    my galls started out clear …. I thought they resembled pearl onions very closely …and the more mature ones I mistook for opportunistic plants because of the windseed like matrix inside the dried paper gall. I’d been doing shishkabob and really did wonder if the opaque/clear seemingly gelatinous filled “balls” were edible. Wow …wasps …who’d a thunk it

  13. Brad Miller says:

    I just discovered these this year around and in some of my trees in central Pennsylvania. I have found several attached and growing on the ground so it appears it does not need the Oak tree itself to form these Galls. I am 50 years old and have never seen these before and had trouble finding out what they are. They look very much like plant growth and never suspected they are insect related.

  14. dayna says:

    They are in fact galls formed by a wasp larva. They are definitely not bagworms. The material of the gall, from it’s external shell to the fruity pulp are all produced by the tree in response to the wasp. The worm eats the puplp until all that is left is the fluffy fibre.