North American Herb Gall Wasps - What We Know So Far, and What is Still Needed!

Hi all! It's been a while since I've sent out a large update on Aulacideini in North America, and with Gall Week this coming week, there’s no better time to provide an update. For anyone that doesn't know me, I'm a fourth-year PhD candidate at Penn State, and part of my dissertation involves taxonomic work of several kinds on North American herb gall wasps. In this post, I'll provide an overview of knowledge on these insects, as well as some key targets that require more observation and collection. The fantastic iNaturalist community has sent me many specimens comprising many species (including many new to science!), and I’m once again reaching out to this platform to help me find even more species.

This is a long and fairly exhaustive post, but each section includes distribution data so you can easily search for species that might occur in your area. For a more detail-oriented treatment of these insects, check out my recent open-access (=free download) field guide, although it's somewhat outdated only 10 months later.

At the end of this post is a list of key targets for collection this year! Please do examine this list and see which species you might be able to find in your area.


Click on the section names below to go to that section!

Section 1: Introduction

Section 2: Microseridinae Gall Wasps

Section 3: Lettuce Gall Wasps

Section 4: Silphium Gall Wasps

Section 5: Hawkweed Gall Wasps

Section 6: Other Assorted Gall Wasps

Collecting and Rearing Herb Gall Wasps

Key Targets for Collection


Many of you are likely familiar with oak galls induced by wasps of the tribe Cynipini. However, gall wasps induce galls on a vast array of host plants, and those other than oak gall wasps have not received much study in recent years (or ever!). My focus is on gall wasps associated with herbaceous plants (i.e., often short lived plants that are not trees or shrubs). In North America, cynipid galls on herbaceous plants are induced by species belonging to three tribes: Aulacideini (my primary focus), Diastrophini (these primarily gall Rubus and Potentilla), and Phanacidini (two known species, both introduced from Europe).

As published in my recent catalogue of North American gall wasps, there are 21 species of the tribe Aulacideini known in North America. However, very early on in my study, it was immediately obvious that our current knowledge only scratched the surface. Thus far, I've encountered as many as 50 total species of Aulacideini in North America, many of which are undescribed species (i.e., new to science) that I intend to describe. In addition to many new species, the two genera of Aulacideini present in North America (Antistrophus and Aulacidea) are polyphyletic, meaning that they contain species representing several different lineages that are not closely related. Because of this, many species of North American herb gall wasps will need to be moved to new genera that will be established as a result of my studies. All in all, there are clearly many classification problems in this group that I am aiming to resolve with my studies.

This post will be split into several sections based on the host plant taxon. Each section will begin with a table outlining the known gall wasps on that host taxon, including the following information:

  1. Species name
  2. An representative observation of a gall (hyperlinked to the species name)
  3. Distribution
  4. Host plant species
  5. Plant organ galled
  6. A brief description of the gall's shape or general appearance
  7. Whether I have successfully acquired adults of that species (which are needed to describe or redescribe a species)
  8. Whether I have successfully sequenced the DNA of that species (mighty helpful in describing a species)

Please peruse this list to learn about progress on my research, and what material you might be able to collect to help understand the biodiversity of this group of insects! If you have any questions about these insects, or galls and wasps in general, do feel free to comment below or message me otherwise! At the end of the post, I have included some information on collecting and rearing herb gall wasps if you'd be so kind as to collect some material on my behalf. Anything listed in this post as not sequenced or without adults known is of high priority for collection!

Microseridinae Gall Wasps

The species in this group all induce galls on a subgroup of the lettuce tribe (Asteraceae: Cichorieae: Microseridinae). These wasps appear to form a monophyletic group (i.e., a “good group” that contains an ancestor and all of its descendants) and appear to comprise three true genera.

Species Distribution Host plant Galled organ Gall shape Adults? Sequenced?
Antistrophus pisum Midwestern and Western US + adjacent Canada Lygodesmia juncea Stems Pea-shaped Yes Yes
Antistrophus sp. nov. Midwestern and Western US + adjacent Canada Lygodesmia juncea Stems Spindle Yes Yes
Antistrophus sp. nov. Midwestern and Western US + adjacent Canada Lygodesmia juncea Basal stems (usually below soil!) Amorphous Yes Yes
Antistrophus microseris California; one record from Arizona Microseris douglasii Stems Spindle Yes Yes
Antistrophus sp. nov.? California Microseris paludosa Stems Spindle No No
Antistrophus sp. nov. Southcentral US; Texas and Oklahoma Pyrrhopappus grandiflorus Stems Cluster/spindle Yes Yes
Antistrophus sp. nov.? California Uropappus lindleyi Stems Cluster/spindle No No

Gall wasps on plants belonging to the Microseridinae appear to comprise a fairly diverse group. It is likely that undescribed species exist on other species of Microseris (of which there are many), as well as other genera in this group such as Agoseris. There are also several additional species of Lygodesmia in the Midwestern and Southern US that could be hosts for undescribed gall wasps.

At this time, it is unclear whether galls found on Microseris paludosa and Uropappus lindleyi are new host plant records for Antistrophus microseris or if these galls truly represent new species. Given the restrictive host plant range of most herb gall wasps, it is quite likely that these are new species, but DNA sequences and examination of adult wasps would be necessary to confirm this.

Lettuce Gall Wasps

Species in this group all belong to the genus Aulacidea, the most diverse herb gall wasp genus comprising more than 40 species known in North America and Eurasia. Aulacidea is in desperate need of reclassification, as the vast majority of species classified here do not belong. In fact, only the species of gall wasps classified in Group B are properly classified in this genus!

Species Distribution Host plant Galled organ Gall shape Adults? Sequenced?
Aulacidea podagrae Widespread in Eastern and Midwestern US Lactuca biennis Stems Variable; cluster- or node-like Yes Yes
Aulacidea sp. nov. Widespread in Eastern US Lactuca biennis Stems Cryptic cells hidden in stem tissue Yes Yes
Aulacidea abdita Eastern US and Canada? Lactuca canadensis??? Stems Cryptic cells hidden in stem tissue Yes No
Aulacidea harringtoni Widespread in Eastern and Midwestern US Lactuca canadensis Stems Cryptic cells hidden in stem tissue Yes Yes
Aulacidea tumida Widespread in Eastern and Midwestern US Lactuca canadensis Stems Variable; usually clavate or spindle-like Yes Yes

The lettuce gall wasps comprise several species of host-specific wasps that induce either visible or cryptic (hidden) galls. Thus far, I have confirmed the identity of lettuce gall wasps on only two species of lettuce, Canadian lettuce (Lactuca candensis) and tall blue lettuce (L. biennis), although there are several other lettuce species in North America.

Several species in this group have uncertain host affiliations. Aulacidea abdita was described by Alfred C. Kinsey in 1920 from adults dissected from old stems that he considered to be Canadian lettuce. Unfortunately, his specimens were greatly damaged (the stems were over 40 years old by the time he dissected them!), but several characters of the head and wings make this species distinct enough. I have not yet encountered this species amongst material my collaborators and I have reared, and I am rather doubtful that Canadian lettuce is the correct host plant for this species. Similarly, we have found galls resembling Aulacidea podagrae on Florida lettuce (Lactuca floridana), but the identity of the inducer remains unclear.

Overall, collecting material from more lettuce species is essential in understanding the biodiversity of these insects, and will help us better understand which plants are used by which wasps. At this time, it seems that only native lettuce species are galled by cynipid wasps.

Silphium Gall Wasps

This group is by far the most diverse group of Aulacideini in North America. Species associated with plants of the genus Silphium were originally found on just four Silphium species, but we’ve found many new species and many new host plants since the last major studies of the group. Species in the below table are grouped based on the location and type of gall they induce.

Species Distribution Host plant Galled organ Gall shape Adults? Sequenced?
Flower Gall Wasps (Antistrophus laciniatus species complex) Apparently widespread in Eastern, Midwestern, and Southern US Flowers Kernel-shaped galls, solitary or clustered, often hidden in disc flower
Antistrophus bicolor Silphium integrifolium Yes Yes
Antistrophus laciniatus Silphium albiflorum, S. laciniatum, S. terebinthinaceum Yes Yes
Antistrophus sp. nov. Silphium perfoliatum Yes Yes
Antistrophus sp. nov.? Silphium gracile Only a few old adults from museum collections No
Globular Stem Gall Wasps Apparently widespread in Eastern, Midwestern, and Southern US Stems Large, round to clustered swellings
Antistrophus silphii Silphium asteriscus var. trifoliatum, S. compositum, S. gracile, S. integrifolium, S. perfoliatum, S. radula Apical stems Large round galls, often at tips of short stems Yes Yes
Antistrophus sp. nov. Silphium integrifolium Lower stems Clustered galls, on middle or lower stems Females only! No
Antistrophus sp. nov. Silphium perfoliatum Lower stems Clustered galls, on middle or lower stems Males only! No
Cryptic Gall Wasps Apparently widespread in Eastern, Midwestern, and Southern US Cryptic cells hidden within tissue
Antistrophus jeanae Silphium perfoliatum Stems Yes Yes
Antistrophus meganae Silphium terebinthinaceum; also hybrids of S. terebinthinaceum and S. laciniatum Stems Yes Yes
Antistrophus minor Silphium laciniatum Stems Yes Yes
Antistrophus rufus Silphium laciniatum Stems Yes Yes
Antistrophus sp. nov. Silphium laciniatum, S. terebinthinaceum Leaf veins and petioles Yes Yes
Antistrophus sp. nov. Silphium asteriscus var. trifoliatum Stems Yes Yes
Antistrophus sp. nov. Silphium dentatum Stems Yes Yes
Antistrophus sp. nov. Silphium integrifolium Stems Yes Yes
Leaf Blister Gall Wasps — unsure how many species, but all undescribed! Apparently widespread in Eastern, Midwestern, and Southern US Silphium gracile, integrifolium, radula Leaf membrane along midrib Large blisters in leaf tissue, most apparent on underside of leaf No No

Comprising at least 14 species, Silphium gall wasps represent one of the most diverse gall wasp communities associated with a single plant genus, behind those on oaks and roses. Given the uncertain status of several species (especially those inducing leaf blister galls), further sampling of Silphium is essential within further understanding the diversity of these insects. Brock and Weakley’s 2020 treatment of Silphium recognizes 27 species and varieties, and thus far we’ve only sampled a handful for the presence of cynipid galls. The remaining ~20 Silphium taxa are almost certainly hosting a tremendous diversity of gall wasps, and there are almost certainly undiscovered gall morphotypes. Our sampling has focused on the Midwestern Silphium, but species in the Southeast and Southcentral United States are prime targets for further sampling.
Interestingly, the vast majority of Silphium gall wasps are specialists on a single host plant. Each species of Silphium gall wasp likely occurs throughout the range of its respective host plant(s), although it’s unclear whether all Silphium populations are capable of sustaining gall wasps. It seems that the wasps prefer large, native populations, although prairie restorations are also frequently found to contain galls.

Hawkweed Gall Wasps

Species Distribution Host plant Galled organ Gall shape Adults? Sequenced?
Aulacidea hieracii Great Lakes area Hieracium umbellatum and possibly other Hieracium Stems Fusiform to clavate Yes (but more would be good!) Yes (but more would be good!)
Aulacidea pilosellae Canada? Pilosella spp. Leaves Blister No No
Aulacidea subterminalis US & Canada? Pilosella spp. Stolons Elliptical to clustered No No
Aulacidea sp. nov. California (only one record so far) Hieracium albiflorum Leaves Blister No Yes (from dissected larvae)

Several species of herb gall wasps induce galls on true hawkweeds (Hieracium) and mouse-eared hawkweeds (Pilosella). Two of these species have been introduced as control agents for invasive plants, and it’s unclear whether the other species are native or represent introduced populations.
I recently found the first known galls of a species inducing leaf galls on Hieracium albiflorum in California! Thus far, I have been able to sequence the larvae of this gall wasp, but we have not yet been able to rear adult insects, which would be necessary to describe this species.
It’s quite likely that more species in this group exist, as we have not heavily sampled hawkweeds in North America. Searching prominent native species such as rattlesnakeweed (H. venosum) would be a great way to find potential new species.

Other Assorted Gall Wasps

Species Distribution Host plant Galled organ Gall shape Adults? Sequenced?
Aulacidea acroptilonica Pacific Northwest Rhaponticum repens (this species has been classified in many genera over time) Stems Fusiform to clustered Yes Yes
Aulacidea sp. nov. California Unknown! Unknown! Unknown! Yes (only old museum material) No
Aulacidea nabali Widespread in Eastern and Midwestern US and Canada Nabalus spp. Lower stems, often below soil line Elliptical to clustered Yes (only old museum material) No
Antistrophus chrysothamni Arizona Chrysothamnus??? Stems Elliptical to clavate Yes (only old museum material) No
Liposthenes glechomae Widespread Glechoma hederacea Stems and leaves Blister-like to elliptical Yes Yes

These taxa are those that don’t fit neatly into another category and represent several different lineages. Several of these species are poorly characterized, known only from a small series of museum specimens, and one new species is known entirely from four female specimens collected in California.

In the case of Antistrophus chrysothamni, the species was first described in 1908, and it has been nearly a century since a valid record has been taken. The species was originally described as galling Chrysothamnus, but no galls matching those of this wasp have since been found on these plants. As a result, it is unclear what the true host plant is for this species, and acquiring new material would be essential in understanding the biology and classification of Antistrophus chrysothamni.

Collecting and Rearing Herb Gall Wasps

Collecting herb gall wasp galls is the most rewarding way to study these insects. Collecting and rearing a single gall will likely yield a great diversity of insects, including the offspring of the gall inducer as well as parasitoids and other gall inhabitants.

Many herb gall wasps induce what are called “cryptic” galls , meaning they induce galls that are not discernable based on external changes to the plant tissue. The widespread presence of cryptic galls has likely greatly contributed to our lack of knowledge about these insects due to the inherent challenges in locating and sampling them. Cryptic galls are best located by finding a large population of a potential host plant and dissecting a series of stems. Stems containing cryptic galls will likely display numerous oval-shaped chambers within the stem tissue as well as numerous larvae inhabiting the chambers. Once you’ve confirmed the presence of cryptic galls, you should collect entire stems of that plant. You can cut them into pieces to store and rear them (see remarks in the following paragraphs). In most cases, the base of the stem is the most densely populated part of the stem, so you should be sure to collect the entire above-ground part of the stem when sampling for cryptic galls.

The following excerpt from our Field Guide to Herb and Bramble Gall Wasps of North America provides an overview for collecting cynipid galls. If you have any questions about collecting or rearing these galls, please do not hesitate to contact me!

“Collecting and rearing a gall is perhaps the best way to verify its identity. Adult gall-inducing insects can provide a wide breadth of data related to galls. Luckily, herb and bramble galls are relatively easy to collect and rear, especially in comparison to oak galls.
Herb and bramble galls should be collected starting in the late Fall, ideally after the first frost of the season has occurred, and can be collected up until the emergence period of the residing insects (late Spring through Summer). For galls on herbaceous plants, it is usually best to collect them after the host plant has senesced; doing so ensures that the larvae developing inside the gall have had plenty of time to mature and feed on the gall tissue.
Rearing these galls (that is, successfully obtaining adult insects from a field-collected gall) is rather straightforward. Galls should be placed in a rearing container like a disposable plastic cup or zip bag. Air holes that are small enough so as to prevent the escape of emerging insects should be poked to prevent the growth of mold. Additionally, they need to be stored somewhere that allows exposure to natural climate fluctuations similar to those of their natural habitats. The authors of this guide recommend that, if possible, galls be left in an open-air shed without climate control. Galls may also be stored in a tight-fitting bin or container provided that they are allowed to expe- rience temperature fluctuations and mold growth is prevented.
You might notice that gall wasps are not the only insects to emerge from galls. Many other insects, especially parasitoid wasps, exploit the shelter and resources of existing galls to feed their own young; these insects are often reared from galls instead of, or alongside, the true gall inducers.
Insects reared from galls can be preserved by storing them in alcohol (ideally 90- 95% ethanol) or by mounting them; there are many useful resources for insect preservation that may be consulted for information on this process.”

Key Collection Targets

Key collection targets are organized into three groups: known species that require further sampling, a list of host plants that are likely to host gall wasps, and a list of plant genera that are more speculative in their possible role as gall wasp hosts. Use the following hyperlinks to navigate these lists:

List of Known Gall Wasps to Look For

List of Likely New Host Plants

List of Speculative Host Plant Genera

List of Known Gall Wasps to Look For

The species in this list are known species that require more study before description or re-description.

Genus and species Host plant Host organ galled Distribution
Antistrophus spp. Silphium spp. Leaves (blister galls) Widespread
Antistrophus chrysothamni Chrysothamnus? Stems Arizona
Antistrophus laciniatus Silphium albiflorum (I have sequence data for other known hosts already) Flowers Texas
Antistrophus sp. nov.? Microseris paludosa Stems California
Antistrophus sp. nov.? Uropappus lindleyi Stems California
Aulacidea nabali Nabalus spp. Lower stems (often below soil) Widespread in Eastern US and adjacent Canada
Aulacidea sp. nov. Hieracium albiflorum (possibly other species too) Leaves (blister galls) California; probably more widespread

List of Likely New Host Plants

The plant species listed in this table belong to genera that host gall wasps, but gall wasps have yet to be found on these specific species. Given the host use trends of known species, it is quite likely that these plants host gall wasps (and probably species new to science) given that other species in their genera are hosts.

Family Genus and species Distribution Possible galled plant parts
Asteraceae Hieracium Widespread in US and Canada Stems, stolons, and leaves
Hieracium abscissum Southwestern US and Mexico
Hieracium argutum California
Hieracium bolanderi Southwestern US and Baja California (Mex.)
Hieracium brevipilum Southwestern US
Hieracium carneum Southwestern US and Chihuahua (Mex.)
Hieracium crepidispermum Southwestern US and Mexico
Hieracium fendleri Southern US and Mexico
Hieracium greenei Pacific Northwest
Hieracium gronovii Eastern North America
Hieracium horridum Pacific Northwest & Nevada
Hieracium longiberbe Pacific Northwest
Hieracium longipilum Central US and Canada
Hieracium megacephalon Southeastern US
Hieracium nudicaule Pacific Northwest
Hieracium paniculatum Eastern North America
Hieracium parryi Pacific Northwest
Hieracium pringlei Southwestern US
Hieracium robinsonii Far North (Maine, New Hampshire, and adjacent Canada)
Hieracium scabrum Eastern North America
Hieracium schultzii Texas and Mexico
Hieracium scouleri Northwestern North America
Hieracium traillii Appalachian and Mid-Atlantic US
Hieracium triste Western US
Hieracium venosum Eastern North America
Hieracium vulgatum Northern North America
Asteraceae Lactuca Widespread in US and southern Canada Only stem galls known (both cryptic and visible galls) but other organs may have undiscovered galls
Lactuca floridana Widespread
Lactuca graminifolia Southern US
Lactuca hirsuta Widespread
Lactuca ludoviciana Southern and Midwestern US
Asteraceae Lygodesmia Widespread in Western US; also Florida and Georgia Stems (both upper stems and basal stems below soil)
Lygodesmia aphylla Florida and Georgia
Lygodesmia grandiflora Western North America
Lygodesmia ramosissima Texas and Mexico
Lygodesmia texana Southcentral US and Mexico
Asteraceae Microseris Western North America, mostly West Cost Stems
Microseris acuminata West Coast
Microseris bigelovii West Coast
Microseris borealis West Coast up to Alaska
Microseris campestris California
Microseris elegans California
Microseris howelii Oregon
Microseris laciniata West Coast
Microseris nutans Widespread in Western US and Canada
Microseris sylvatica California
Asteraceae Pyrrhopappus Widespread in Eastern and Central US Stems
Pyrrhopappus carolinianus Eastern and Central US
Pyrrhopappus pauciflorus Texas and Mexico
Pyrrhopappus rothrockii Arizona, New Mexico, and Texas
Asteraceae Silphium US and parts of southern Canada Stems, flowers, leaves (both cryptic and visible galls)
Silphium albiflorum Texas
Silphium asperrimum Southcentral and Southeastern US
Silphium asteriscus (and varieties) Southeastern US
Silphium brachiatum Southeastern US
Silphium compositum (and varieties) Southeastern US
Silphium confertifolium Alabama
Silphium connatum Mid-Atlantic US (VA, WV, NC)
Silphium dentatum Southeastern US
Silphium glutinosum Bibb County, Alabama
Silphium gracile Southcentral US
Silphium mohrii Appalachian US
Silphium perplexum Alabama
Silphium pinnatifidum Appalachian and Southcentral US
Silphium radula Southcentral US
Silphium reniforme Southeastern US
Silphium simpsonii Southeastern US
Silphium speciosum Lower Midwestern US
Silphium wasiotense Appalachian US

List of Speculative Host Plant Genera

The plant genera listed in this table might host gall wasps based on relatedness to taxa already known to host gall wasps. These taxa are much more speculative than those in the above table, but may prove to be hosts of notable gall wasp diversity.

Plant Genus Distribution
Subtribe Crepidinae (2 genera listed here; this tribe includes Nabalus which has a known gall wasp) Widespread in North America
Crepis (Several native spp. worth checking) Widespread in North America
Taraxacum (Several native spp. worth checking) Widespread in North America
Subtribe Microseridinae (18 genera listed) Primarily western North America
Agoseris (11 spp.) Western North America
Agoseris (11 spp.) Western North America
Anisocoma (1 sp. – A. acaulis) Southwestern US
Atrichoseris (1 sp. – A. platyphylla) Southwestern US and Northwestern Mexico
Calycoseris (2 spp.) Southwestern US and Northwestern Mexico
Chaetadelpha (1 sp. – C. wheeleri) Southwestern US
Glyptopleura (2 spp.) Southwestern US
Krigia (7 spp.) Eastern North America
Malacothrix (18 spp.) Western US and Northwestern Mexico
Marshalljohnstonia (1 sp. – M. gypsophila) Coahuila, Mexico
Munzothamnus (1 sp. – M. blairii) California
Nothocalais (4 spp.) Western and Central North America
Pinaropappus (2 US spp.) Southern US and most of Mexico
Pleiacanthus (1 sp. – P. spinosus) Western US
Prenanthella (1 sp. – P. exigua) Southwestern US
Rafinesquia (2 spp.) Southwestern US
Shinnersoseris (1 sp. – S. rostrata) Central North America
Stephanomeria (14 spp.) Western North America
Posted on August 29, 2023 07:47 PM by louisnastasi louisnastasi


Tagging some of the folks I think might appreciate this more-detailed post:
@calconey @megachile @nancyasquith @arbonius @graysquirrel @friesen5000 @ceiseman @adeans

Posted by louisnastasi 11 months ago

I love this, well done Louis!

Posted by mileszhang 11 months ago

This is great!

Posted by beartracker 11 months ago

Wow, great work! I didn't know this function of iNat. Very useful.

Posted by antoine_guiguet_ 11 months ago

Incredible work here!

Collecting/surveying some L floridana is on my agenda for my fall gall trip this year... supposedly we have L hirsuta here as well although there is really only one good modern herbarium record for the whole state.

I have never seen (noticed) the Silphium leaf blister galls here in Ohio, but I will run through a few sites this fall and see if I run into any.... looking like I wont be getting back into the south for some new Silphium species until next spring.

I have not really look at hawkweed with any seriousness, and they are somewhat common so will start to keep an eye out for them when I run into them. Looks like we have a handful of species here in OH

I have looked at quite a bit of Nabalus with no success so far, even at pretty dense sites... wondering about timing on this one, and going to keep track of how these die down so I can find them during the winter this year.

Crepis and Krigia is decently common here so that goes on the list as well...

Posted by calconey 11 months ago

@calconey The second-ever iNat observation of Aulacidea nabali was just posted from northeastern Canada so the galls should be developed at our latitude at this time. I'm planning a trip to find it this weekend at a nearby preserve with records of Nabalus - hopefully I find some! Cryptic galls are definitely worth searching for on these plants as well.
Thanks for keeping an eye out! I'm sure we'll come up with some interesting taxa this coming season.

Posted by louisnastasi 11 months ago

I found this post while searching for a possible gall-inducer on Prenanthella exigua, which is among the "speculative host plant genera" listed above. Observation here:
In some areas, ~50% of the plants had this same gall. I can probably collect and try to rear some!

Posted by lithostrotionella 3 months ago

@lithostrotionella those could certainly be an undescribed gall wasp - the best way to tell what kind of insect induced them is to take a simple cross section. If you’d be willing to collect some of these, I could also sequence the DNA of the insects inside. Based on what I’ve seen, these could be a new genus and not just a new species. I’d be greatly interested in anything you’re able to find!

Posted by louisnastasi 2 months ago

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