Spring Oak Gall (wasp) hunting

In the last couple years, as @jeffdc and I have built gallformers.org, the interest the iNat community has shown in galls has grown tremendously. It’s been very satisfying to see and I want to thank all of you who’ve participated.

Between the work of some taxonomists and iNat observers, I think we are at the cusp of a very productive period in which a lot of undescribed species will be collected, life cycles closed, and phenologies defined. At any given location, the majority of that work will take place within a period of about three months around budbreak. As I did a couple years ago, I’d like to ask those of you who are interested to make a focused effort to look for wasps and sexgen galls within that window. The reward is that you’re very likely to find an undescribed species or generation and maybe get your name on it.

For background, in case you aren’t aware:

Oak gall wasps (cynipini) have a bivoltine or two generation life cycle, each inducing a totally different gall. One generation includes males and females (the bisexual generation or sexgen), the other only females (unisexual or agamic). With the caveat that as always in nature there are exceptions, the generic cynipini life cycle goes like this:

  • From late fall to early spring, agamic females emerge and lay eggs in winter oak buds
  • Around the time of leafout, sexual generation galls develop within bud scales or on bud-breaking leaves and flowers
  • Shortly after budbreak, male and females of the sexual generation emerge to mate. Females oviposit on still-green leaves and first-year stems, where agamic galls develop and wasps stay dormant until emergence (sometimes only a few months, sometimes up to a few years).

A relatively small proportion of species are known from both generations, because sexgen galls are often cryptic and short-lived. Additionally, we have very limited information about the emergence timing of agamic wasps for most species. If you’re interested in helping fill in those gaps, I’d like to offer a tool, make a few requests, and point you to some priority targets.

My tool calculates a range of dates as a function of latitude. Eg Dryocosmus quercuspalustris at 44 degrees N, is predicted to emerge May 18-July 23, and at 30 degrees N, February 16-April 19. I’m hoping that by spring, we’ll have a page on gallformers.org where you can input your current latitude and get the emergence period for gall inducers for which this info is available. For now, I’ve included a few examples. If you’re interested in anything specific, please ask and I can tell you directly for now. The general point is just that it’s worth looking closely at oaks earlier and harder than you might expect.

Right now, a lot of those models are probably not very good. For most species, I don’t have a single data point. I am planning to publish the current estimates to empower you to go out and test them, so I can make better ones. To improve the models, the two most valuable observations are emergence and free-living adults. If you go looking for galls this spring:

  1. If you see an adult wasp ovipositing on an oak bud (eg), take photos, but also collect it. That way we can confirm the ID and potentially use it for genetic sequencing.
  2. If you see sexual generation galls on buds or leaves, collect them and put them in a container to rear the adults. They should emerge shortly if they don’t die.
  3. If you don’t want to rear, or if there are a lot of galls, dissect to check the inducer’s presence and life stage. Many galls are phenologically ambiguous based on external appearance; dissecting provides more concrete information.

If you get an adult, put it in ethanol (95% ideal, 70% in a pinch) in the freezer and let me know you have it. Otherwise just make sure it’s labelled clearly and in a way that won’t become unreadable in case of a spill (eg pencil and pen both run in ethanol). Printer ink works well if printing labels is convenient. Otherwise just label the outside of a double sealed container.

At this point, data is scarce enough that nearly anything is valuable. But personally these would be my highest priorities:

North of 35 N on white oaks, before budbreak:

  • Disholcaspis agamic females ovipositing in spring. There are no records of this in the literature north of FL, TX, and NM, but I am convinced it is common based on iNat records. I just need an adult specimen to send to a taxonomist to confirm. You don’t need to know what a Disholcaspis adult looks like–for one thing, I’m not sure that’s what they are, and no matter what you find they’ll be valuable. These theoretically could emerge any warm day in the winter with stragglers into the late spring but I’d look for these in the month before leafout–at 45 N it would be April 12-May 1, at 35 N more like February 20-April 1.

On Quercus alba, in early summer:

  • Callirhytis clavula adults. This wasp has not been reared in nearly a century and we’re not entirely sure whether it is an agamic or sexgen gall. It would be great to have new specimens. This is a very common species in some areas and cross sections during the growing season would be very informative. The estimated emergence period is May 3-July 16 at 35 N and July 2-Sept 1 at 45 N.

In eastern NA (and Mexico), on all red oaks, after budbreak:

  • Any Amphibolips wasp or gall. We have a collaborator actively working on the genetic phylogeny of this genus and he is desperately undersupplied with specimens. There are a lot of cases in this genus where sketchy synonymies have been made across large ranges and on different hosts so it would be valuable to get samples from people all over. Lots of undescribed species in this genus too. North of Mexico, Amphibolips sexgen adults are predicted to emerge from approximately March 21-May 2 at 30 N and May 25-July 10 at 40 N.

In California, on white oaks:

  • The phenology of Burnettweldia plumbella is confusing. The lit reports galls developing in May, mature by September-October, and emerging in Nov-Dec. But iNat observations seem to show emergence much earlier than that, and maybe developing galls in the winter in southern CA? I would love to have more cross-sections of this species throughout the year, since these observations are tough to evaluate from the outside (hard to tell how old the gall is or when the hole was made).

In California on Q lobata, after budbreak:

  • The sexgen galls of Andricus kingi were described in 1971 but there isn’t a single color photo available. Look on Quercus lobata trees with lots of A kingi galls in previous years. They’ll be integral leaf galls with conical tips. See Figure e on page 3 here.. Emergence estimated around March 31-April 26 in LA and May 6-June 2 by Redding; look for the galls in the weeks before those dates. It would be ideal to have adults reared from the galls both for the phenology and to confirm the ID; these sexgen galls are hard to distinguish from gall morphology, especially with the minimal info we have now.

In California, on intermediate oaks (Q chrysolepis and vacciniifolia), after budbreak:

  • Any integral leaf gall is likely an undescribed species; this host group is extremely understudied relative to the number of galls observed.

Thanks all, and happy gall hunting!


Great post, Adam. I am cautiously optimistic about photographing an adult Cynipid this year. I’ll try to remember to throw some vials in my pockets when I’m looking.


I’ll put some (more) vials in my field pack as well. Happy to help, if I can!


I’m definitely looking forward to the upcoming gall season, hoping to find many new galls in the Southern Ohio area.


I’ll be happy to look & document, but to collect in Alabama even inverts now need ALDCNR permit to my understanding. If you confirm/get one and can list me on it, I’d be happy to collect - it can be a bit slow but it’s a simple one page form. (We need one for our cave work that does list inverts we work with, and so I don’t want to risk future permitting issues even if ‘no one cares’ on private land.) Feel free to DM me.

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Solved this one already–turns out these are a totally different group of wasps, the white-group oak root gallers. Holocynips and likely related species like Callirhytis ellipsoida. These adults do seem relatively apparent so keep an eye out for them but this is no longer an urgent mystery in my mind.


Fascinating post! Will have to keep an eye out in the Spring and early Summer when I go hiking in the Long Island area.


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