28 de enero de 2024

Old Ants, New Discoveries

I've been working with the WWU Insect collection for several months now, sorting and reviewing specimens that have been recently donated as well as those that have been neglected for a long time. For the last few weeks, I've been working on the collection's ants, and I've come across multiple very interesting specimens that had until now gone unnoticed.

The first of these is a group of about 20 specimens, collected in 1963, representing to my knowledge the very first record of Formica subelongata collected in Washington state. Until this point, the specimens had been labeled as "Camponotus herculeanus pennsylvanicus" (now simply Camponotus pennsylvanicus) -- how they went so long unchecked, I have no idea. No hate to the wonderful staff and volunteers who have helped to maintain the largest remaining public entomology collection in western Washington -- there is a lot to curate and not a lot of time for it. We will be imaging these specimens next week and sending the data to AntWeb. Perhaps more interesting, however, is the discovery of a very unusual Formica sanguinea group gyne, funnily also collected in 1963, that is unlike any prior records I could find. This gyne has an apical bump or peak emerging from the crest of its petiole, which to my knowledge has not been observed among any known sanguinea-group gynes. The specimen, as well as a full unit from the same geographical area consisting of an alate gyne with the same unusual feature and several workers collected from the same nest, most closely resemble Formica aserva, however, F. aserva gynes to my knowledge are still not known for this feature.

It should be noted that Formica aserva especially has highly variable petiolar morphology. Almost all specimens, both queens and workers, exhibit a petiole that is broad and fan-shaped, however, the crest of the petiole when looking from the head towards the gaster can vary significantly even among workers from the same colony. The two most common patterns among workers are a symmetrical topography with a central notch and short peaks to either side of the notch followed by a normal smooth convexity moving further to the side, and an irregular, asymmetrical topography which may or may not have a central notch, has a single peak to only one side of the center, and often a bumpy or wavy convexity along the rest of crest. Irregular patterns of petiole topography in F. aserva is far more common and more extreme among workers, with gynes most often exhibiting a smooth symmetrical topography with or without a central notch. As of now I have not yet seen petiolar morphology in F. aserva gynes matching what I have observed in these two specimens, and I have not seen it in any workers, including the specimens in the collection here.

Based on the very limited data available, I hypothesize that these specimens represent either a mutation among F. aserva gynes that results in infertility, or a morphologically distinct subspecies of F. aserva. More specimens and colonies will need to be collected and analyzed to explore these possibilities. In the meanwhile, reaching out to naturalists through platforms such as this one to mount and photograph Formica aserva gynes they collect may help answer some questions. I'll update on this in another journal entry later on down the road with photographs and any new information I encounter. Cheers!

Publicado el enero 28, 2024 12:18 MAÑANA por critters_pnw critters_pnw | 0 comentarios | Deja un comentario

05 de junio de 2022

A tentative key to workers in the Formica sanguinea species group

The following is based on specimens hosted on AntWeb and information described by AntWiki. It is likely not a complete or comprehensive guide to identification and will need review but is to the best of my knowledge accurate to current published data.

NOTE: The species Formica obtusopilosa and Formica perpilosa resemble sanguinea-group species in that they may have a clypeal notch. However, they are currently considered to belong to the neogagates species group and can typically be distinguished by their small size, higher-set eyes, and more rounded heads.

Palearctic, typically European but reportedly occasionally occurring in Central Asia -- Formica cf. sanguinea

Nearctic: throughout mainland North America between Alaska and northern Mexico. Rare or not occuring in southeastern states -- (2)

Entire body including gaster mostly or entirely concolorous and shining -- (3)

Body clearly bicolored with brown or black gaster; if appearing somewhat concolorous, gaster pubescent -- (4)

Intensely red or orange in coloration, occuring locally in northwestern states from Washington to Oregon and Montana, possibly north into British Columbia -- Formica curiosa

Darker and less uniform in coloration. Crest of propodeum angulate and length of clypeus from frontal area to clypeal margin notably exceeding length of frontal lobes. Uncommonly collected, occuring in midwestern states or occasionally in New England -- Formica creightoni

Mesonotum small or "saddle-backed" in profile, forming a small but distinct step up from pronotum; crest of petiole lacking erect setae -- (5)

Mesonotum mostly flush with pronotum, forming an uninterrupted curve or if appearing "saddle-backed" setae are present on crest of petiole -- (6)

Bicolored or mostly concolorous and brownish. Commonly collected throughout eastern United States and presumably occurring in eastern Canada; distribution as far southeast as Georgia and as far west as Utah but most often recorded between Illinois and North Carolina to Maine -- Formica subintegra

Bicolored or very weakly if ever concolorous and head dark. Mesonotum significantly smaller than pronotum. Rarely recorded, presumably only occurring in Arizona, Utah, and Colorado -- Formica emeryi

Very few or no erect setae on gaster. Petiolar node broad, typically as wide as propodeum, and resembling a fan, lacking setae on the crest. Widespread, occurring throughout United States and Canada but not present in central and southeastern states (Nebraska south to Texas and east to North Carolina, present sporadically in Appalachia). Especially common at higher elevations in the west including the Rocky, Cascade, and Sierra Nevada Mountains; in the east most often collected in the New England and Great Lakes regions -- Formica aserva

Several erect setae present on dorsum and gaster. Petiolar node smaller with at least a shallow notch and/or setae present on the crest -- (7)

Erect setae on gaster and mesosoma short and/or stiff, bristle-like with inconsistent tapering; petiole with sharp crest. Eastern United States with populations in Colorado and New Mexico -- Formica rubicunda

Erect setae on gaster and mesosoma longer and/or evenly tapered -- (8)

Erect setae on gaster thick and gaster pubescent. Antennal scapes shorter than total length of head. Believed to occur from Quebec south to North Carolina and no further west than the Rocky Mountains except for possibly dubious southwestern populations reported in Utah, Colorado, Arizona, & New Mexico -- Formica pergandei

Erect setae on gaster thinner, longer, and usually less dense -- (9)

Gaster pubescent; propodeum smoothly sloping and lower than crest of petiolar node. Hairs on pronotum appear the same as those on the gaster. Commonly collected in western United States and Canada, especially along the Rocky, Cascade, and Sierra Nevada Mountains -- Formica puberula

Gaster sometimes less pubescent and propodeum more angulate from side profile. Occurring only in central southwestern United States, at most Idaho to Texas -- (10)

Petiolar node unremarkable and blunt, few or no erect setae on mesonotum. Setae on pronotum typically short and blunt -- Formica wheeleri

Petiolar node resembling a spade from side profile, several erect setae present on mesonotum -- Formica gynocrates

Special acknowledgement to @arman_ , @mettcollsuss, and @mazmurlo for input and support

All images are linked to their respective files on AntWiki which contain appropriate reference and licensing information. Listing all the images here would be tedious and take up too much space.

Key to New England Formica. AntWiki. (2018). Retrieved June 5, 2022, from https://antwiki.org/wiki/Key_to_New_England_Formica

Ellison, A. M., Gotelli, N. J., Farnsworth, E. J., & Alpert, G. D. (2012). Field guide to the ants of New England. Yale University Press.

Publicado el junio 5, 2022 10:28 TARDE por critters_pnw critters_pnw | 0 comentarios | Deja un comentario

29 de mayo de 2022

Getting to know thatching ants: a general guide for the Pacific Northwest

If you've ever seen a particularly large anthill covered in dozens, hundreds, or even thousands of black and orange ants, there's a good chance you've come across a thatch mound. In North America, especially the western United States and Canada, these belong to members of the Formica integra species group (in Europe they are built by very similar ants belonging to the Formica rufa species group, and in both Europe and the eastern United States you can also expect to see mounds from ants in the Formica exsecta species group). Often, especially in the Pacific Northwest, observations of these mounds or ants are immediately filed under Formica obscuripes, but this is not always correct. This is because the computer vision software and most users are unaware of and unable to discern minute but important details. At a glance, nearly all ants in the Formica integra species group and the similar Formica sanguinea and Formica exsecta species groups are practically identical. They are all fairly large ants with red-orange heads and black or brownish bodies.

An example of such an ant, in this case Formica obscuripes (Formica integra group):

Original image, all rights reserved

Usually, without decent magnification (usually macro photography or micoscopic analysis) it is impossible to identify these ants to species due to their similarities and range overlaps. The following is a basic, but incomplete guide to breaking these ants down for iNaturalist so that we can mitigate incorrect records. Note that in reality there is much more nuance and that this guide is tailored for the Pacific Northwest, with which I am most familiar. This information is based on personal knowledge and experience as well as Stockan et al. (2016).

integra-group or sanguinea-group?
Members of the Formica integra species group, usually known as thatching ants, are similar in appearance to members of the Formica sanguinea species group. There are a couple ways to discern them, however:

  • The nest: sanguinea-group ants rarely, if ever, construct mounds (piles of dirt and plant materials). They are much more likely to be found living under rocks and especially inside or under logs. On the other hand, integra-group ants may or may not construct a mound depending on the species and location. As a rule of thumb, if a mound is present in the observation, it is Formica integra group. If a mound is not present, identify it as genus Formica (Wood, Mound, and Field Ants).
  • The clypeus: The plate above the mandibles of ants is called the clypeus. The morphology of the clypeus is especially useful in identifying these ants. Formica sanguinea-group ants have a clypeal notch, which is a concave portion at the front of the clypeus. This feature is not present on Formica integra- and Formica exsecta-group ants. This can be difficult to discern sometimes, so if you're unsure then identify it as genus Formica (Wood, Mound, and Field Ants).

An example of the clypeal notch on the Formica sanguinea-group species Formica aserva:

Original image, public domain

The clypeus of Formica obscuripes which lacks the notch:

Original image, public domain

obscuripes or otherwise?
Formica obscuripes is a bit of a celebrity in the ant world. It is one of the best studied species of Formica and one most widely recognized ant species in the United States and Canada. As a result, most integra-group ants are identified on iNaturalist as F. obscuripes without sufficient evidence. In order to accurately identify F. obscuripes or any other Formica integra-group species, a clear view of several parts of the ant is necessary. To make it quicker and easier to understand, I'll just go over differentiating F. obscuripes from a few of its lookalikes. For a more precise and thorough list of integra-group species and their identification, I recommend AntWiki's Key to Nearctic Species in the *Formica rufa Group* (now recognized as the taxonomically distinct Formica integra group). Please note that if you are inexperienced or unsure it is always best to simply identify an observation as genus Formica (Wood, Mound, and Field Ants) or Formica integra group. That way, those with more experience can take a closer look, and if it cannot be IDed to species we don't have to worry about a misidentification floating around.

Three of the most likely species to be confused with F. obscuripes are F. oreas, F. obscuriventris, and F, ravida. F. obscuripes can be distinguished from F. oreas by the setae (hairs) on the antennal scapes, which are the first and longest segments of the antennae. In F. oreas, there are numerous erect and suberect (standing up) setae distributed evenly on the antennal scapes. These setae are usually only slightly shorter than the setae on the rest of the ant's body. In F. obscuripes, there are few if any erect/suberect setae on the scapes and when present they are significantly shorter than the setae elsewhere. The next one, F. obscuriventris, has enlarged clypeal fossae. These are divots where the clypeus meets the rest of the head between the antennae and the mandibles. It can be quite difficult to discern this without experience. The clypeal fossae of F. obscuripes are unremarkable like most other integra-group ants.

An example showing antennal scape setae (red) and clypeal fossae (blue):

From left to right: Alpert, 2011; Prado, 2010; Nobile, n.d. See reference list for licensing information. Images were cropped and combined and names and colored boxes added by author.

Finally, F. obscuripes has extensive, evenly distributed, and usually fairly long erect setae on the head vertex (top of the head from a side profile) and mesosoma (middle section of the ant; thorax). F. ravida and many other integra-group species lack this abundance and even distribution of setae.

An example showing the distribution of setae on the head and mesosoma:

From left to right: Alpert, 2011; Alpert, 2012. See reference list for licensing information. Images were cropped and combined and names added by author

Again, there is a lot more nuance than I would be able to reasonably include in this forum post. My goal here is to bring to light some distinctions between common similar species in the area to improve the quality of community observations and identifications, particularly in the Pacific Northwest. Hopefully this will be helpful to some of my fellow naturalists! Please note that I am also not an expert and this information may not be complete or accurate to literature standards. I am open to feedback and questions.

Alpert, G. D. (2011). Formica obscuripes MCZ001H [Photograph]. AntWiki. (https://www.antwiki.org/wiki/File:Formica-obscuripes-MCZ001H.jpg). Licensed under CC BY-SA 3.0

Alpert, G. D. (2011). Formica obscuripes MCZ001L [Photograph]. AntWiki. (https://www.antwiki.org/wiki/File:Formica-obscuripes-MCZ001L.jpg). Licensed under CC BY-SA 3.0

Alpert, G. D. (2012) MCZ ENT Formica ravida 01hal [Photograph]. AntWiki. (https://www.antwiki.org/wiki/File:MCZ_ENT_Formica_ravida_01hal.jpg). Licensed under CC BY-SA 3.0

Nobile, A., n.d. CASENT0005390 Formica oreas Head View [Photograph]. AntWeb v.8.75.4. (https://www.antweb.org/bigPicture.do?name=casent0005390&shot=h&number=1). Licensed under CC BY 3.0

Prado, E. (2010). CASENT0179609 Formica obscuriventris Head View [Photograph]. AntWeb v.8.75.4. (https://www.antweb.org/bigPicture.do?name=casent0179609&shot=h&number=1). Licensed under CC BY 3.0

Stockan, J. A., Robinson, E. J. H., Trager, J. C., Yao, I., & Seifert, B. (2016). Introducing wood ants: Evolution, phylogeny, identification and distribution. Wood Ant Ecology and Conservation , 1–36. https://doi.org/10.1017/cbo9781107261402.002

Publicado el mayo 29, 2022 11:44 TARDE por critters_pnw critters_pnw | 1 comentario | Deja un comentario