06 July 2010

Identifying Odonata from photographs

We are getting lots more emails these days asking us to identify photographs of damselflies and dragonflies. First let me say that we are thrilled that more people are getting interested in Odonata, and we are happy to help nurture that curiosity. These are still the salad days of odonatology -- we have an enormous amount to learn about the distribution and ecology of these insects. Because their life cycles include both aquatic and upland portions, and since many species are habitat specialists, Odonata are very important indicator species of the health of ecosystems.

Accurate, quantifiable data on Odonata abundance and distribution are invaluable, and it's easy for citizen scientists to make substantial contributions!

In one big long-winded post, we're going to tackle the issues surrounding how to do this regarding photo ID and official records, with a Midwestern-centric focus.

Identifying Odonata from photographs
We disappoint (or piss off) some people when we do not positively identify to species many of the photos that are sent us. There are many pitfalls to identifying odes from photos. We're not being fussy -- these pitfalls should not be taken lightly. Here are a few.
  • Many species can only be identified by close examination in the hand. Honest. We are not making this up. Some examples of genera that fall into this category are many damselflies, especially spreadwings (Lestes) and bluets (Enallagma); the blue darners (Aeshna); many clubtails, especially the dull Gomphus; some emeralds (Somatochlora) and many baskettails (Epitheca); and most meadowhawks (Sympetrum).

    Typically, in-hand ID involves the shape and configuration of the male's claspers and/or hamules; the female's ovipositor, subgenital plates, and/or mesothoracic plates; wing veination; or subtle markings. Or combination of some or all of the above.

    Even when these characteristics are clearly defined, many non-experts still find it difficult, or impossible, to get a positive ID. After nine years of experience, we have a good understanding of ode anatomy and have examined many hundreds of individuals. Yet we can still spend a hour with an ode under a microscope with technical manuals spread out on the table and be stumped.

    There are a slew of cases that illustrate these hazards. Some are garden-variety similar species. Then there is the really weird stuff. Some we hope to cover in detail in separate posts, but a here is an overview.

    • Hybrids and uncertain taxonomy. While not restricted to these genera, the best examples of hybrid, intergrade, or uncertain taxonomy in common species of this are are among the Epithecas and Sympetrums.

      Four species of Epitheca -- cynosura (Common Baskettail), costalis (Slender [Stripe-winged] Baskettail), semiaquea (Mantled Baskettail), and petechialis (Spot-winged Baskettail) pose serious ID challenges in the eastern U.S. Nick Donnelly works on a number of confounding taxonomic challenges, and said this about these species [1]: "Each of these species has proven to be somewhat variable at a single locality and much more so over a wide range. The variability is such that occasional specimens are not easily determined to species." Slender Baskettail was added to the Michigan checklist based on specimens deposited as Common Baskettail in the UMMZ [2]. We added Slender to the Wayne Co. list after collecting a series of baskettails in 2006. Since then we have submitted more specimens to Nick -- it turns out that most baskettails in this area are intermediate between Slender and Common. There is no way humanly possible to discern this with a photograph. And not enough have been collected to determine the geographic range of intergrades, or where different proportions of each species or intergrades occur. Therefore, in this region, this species complex cannot be identified from photographs. Period.

      The problem is similar, perhaps worse, with several common species of meadowhawks. Intergrades and taxonomic murkiness occur in various species nation- and worldwide. In this area they are Sympetrum rubicundulum (Ruby), S. internum (Cherry-faced), and S. obtrusum (White-faced). All sorts of morphological variations occur, especially in the male genitalia. In theory, Ruby and Cherry-faced have red faces, and White-faced are white. Even if this held true, immature individuals present a long continuum of color as they mature. Our collections indicate that in southern Michigan, individuals that closely match the morphology of Cherry-faced are very rare. What appear to be, in the field, Ruby and White-faced are both common, with White-faced tending to stick to wetlands more closely than Ruby. However, a large number of putative Ruby Meadowhawks (or, meadowhawks with reddish faces) have puzzling genitalia that indicate intergrades with Cherry-faced or (probably more likely in southern Michigan, at least) White-faced. We are just starting to look at the morphology of Sympetrums with white faces. We'll get back with you on that. However, Donnelly has been working on this since at least 1991 [3], so don't expect answers soon. By the way, DNA analysis has not even helped clear up this mess -- indicating species differentiation is still taking place. Ergo, we don't feel confident that this species complex can be identified from photographs. Period.

      There is also taxonomic uncertainly in a bunch of the river cruisers (Macromia), and hybrid Enallagma, Gomphus, and Leucorrhinia have also been found.

    • Aberrant individuals. Beyond the range of normal variation discussed below is the issue of truly abberant individuals. In northern Michigan, I (Nannothemis) once caught what I thought was a Variable Darner (A. interrupta) or Mottled Darner (Aeshna clepsydra) based on the thoracic pattern. When I got it home, I saw that the opposite side of the thorax was that of a Canada Darner (A. canadensis). An examination of the claspers and other features verified that it was the latter species [4]. Had I photographed the weird side, the ID would have been incorrect. We don't know how common these types of abnormalities are but they are not without precedent.

  • Inexperience with individual variation. A lot of beginners are not aware that male and female odes are often have different colors or patterns. Many female damselflies have multiple color morphs, sometimes including one "androgenic" morph that looks like a male. Many Aeshna females come in two or three colors, such as green and yellow-striped female Lance-tipped Darners (Aeshna constricta) and blue-striped Shadow Darners (A. umbrosa -- although this may be a separate subspecies). And both males and females go through color changes (in both body and wings, for species with colored wings) between emergence and sexual maturity, a process that takes place over days up to a week or more. Old individuals of some species, especially males, develop a waxy bloom (called pruinescence) on the body and occasionally wings that obscures other patterns. Some odes are a different color when they are cold, or when they are mating.

    There can also be regional differences, often in wing patterns. This is true in those pesky Sympetrum, where some species have a lot of color in their wings in the west, but none in the east. The wing bands of Widow Skimmers (Libellula luctuosa) are paler in the west, but there is range-wide individual variation. The wings of Prince Baskettails (Epitheca princeps) can be heavily or lightly marked.

    While many more experienced ode watchers can correctly identify many variable species, a big problem with photos that are incorrectly identified is that in this digital age they get posted online, perpetuating wrong IDs (see below).

  • Lack of comprehensive visual identification guides. There are an increasing number of good regional "field guides" to Odonata being published (links to some we recommend are in the sidebar). However, not many of them provide enough photos or plates of reliable identification characteristics.

    The majority of people we know don't own an array of ode field guides. Instead, they turn to the Internet to find photos that "match" their own. This is really hazardous! Without proper, verified identification a species name gets attached to a misidentified photo, another person comes along and finds a "match" and misidentifies their photo and sticks it on their web site, and viola! Misidentifications go viral. Too often even when the bad ID is discovered, people don't correct their mistakes online. We have contacted owners of popular web sites and pointed out some off-base IDs. We're thanked, and the correction never gets made to the site. When we identify a cryptic species in one of our own photos, it generally means we've netted it and confirmed the ID in the hand after taking the picture.
The bottom line is that there are species that can be confidently ID'd from an appropriate photo, and a slew of them that cannot. We are just as interested in positive ID's as anybody else -- a favorite quote is by Linneaus: "If you do not know the names of things, the knowledge of them is lost too." But we also accept that we see and photograph Odonata that cannot be named if we did not have an opportunity to examine them in-hand.

Identifying Odonata in the hand
A lot of the newer Odonata guides provide a few pages summarizing the in-hand features of confusing groups -- such as a page of "bluet butts" that illustrate the last several abdominal sections and claspers of the males of each species of Enallagma. A photocopy or scan of these cheat sheets tucked in your field gear enable you to make a giant leap forward in ode identification. You will, of course, need an insect net, and probably a 10x hand lens (although many binoculars can be used backwards for this task). While there will still be some species that require a very close look with technical manuals as reference, using a variety of cheat sheets in the field will allow the positive ID of a ton of commonly-encountered odes. And you'll become familiar with Odonata anatomy, which will increase your field ID skills as well.

A few words about how sensitive odes are to handling: they are not. Butterfly wings can be easily damaged in a net or by being handled. Odes (except for newly emerged individuals) are tough as nails. You can hold them by the wings and look them over without damaging them. If you need to hold onto a few until you get back to the car to consult more books, you can tuck them into glassine envelopes with their wings folded over their backs and tote them around for quite awhile. So long as the envelopes are carried in a hard-sided container to prevent crushing, the odes will be fine and can be examined and released without harm.

No, they don't sting. The big ones can bite, but it's just a mild pinch.

Don't want to carry a net? Then don't expect to correctly identify all the odes you see.

Official records require vouchers
We started out saying that we have a lot to learn about Odonata distribution. We live in Wayne County, Michigan, outside Detroit. It is (and always has been) the most populous county in the state, and is also the most developed. Prior to 1995, there were fewer than 50 species recorded for the county, only 32 verified by specimens. Since 2001 -- in this heavily urban county -- we have nearly doubled the number of species for the county (including several species new to the state) and re-verified nearly all the historical species. If we can do that here, what can you do around your home?

Most states that keep track of their Odonata do so out of their department of wildlife or natural resources, a state university, or museum. For a species to be "official," a voucher specimen needs to be submitted to the appropriate organization. In Michigan, this is the Michigan Odonata Survey (MOS), a project of the University of Michigan Museum of Zoology (UMMZ) Insect Division. Requiring voucher specimens is pretty standard with insects, owing to the difficulty in identifications and taxonomic status of so many species, outlined above. Further, most states don't have well-developed Odonata study programs -- so there isn't a cadre of professionals and amateurs with the expertise to form committees to "judge" sight and photo records. The MOS, for example, is run by Mark O'Brien, UMMZ's collections manager. He's responsible for most aspects of managing a collection of 4.5 million insects. I'm amazed he's had the time to launch and maintain MOS to the extent he has.

The golden rule of the scientific method is that studies should be objective, verifiable, and repeatable. Vouchers help to satisfy that rule in a way sight records and most photos cannot.

Here are some links to collecting policies:
When to collect a voucher specimen
  • State and county records. These are required in Michigan. They are the most solid evidence of distribution, so if you collect anything, collect these new records (see below for which species are needed).
  • New locations. In a county with limited habitat, areas under restoration (or development), or more than one watershed, voucher specimens can help delineate habitat requirements, dispersal over time, extirpations, etc.
  • Unusual or aberrant specimens.
  • Early or late flight dates. Very useful to establish ecological parameters. For species where there is sufficient historical data, it can help shed light on the effects of global climate change (or dispute it, for deniers out there). For those without enough historical data, we may as well start now.
How do I know if it's a new record, or figure out flight dates?
In Michigan, turn to the MOS web site. The best place to look for the most current information is the online specimen database. It is usually current through the previous collecting season, and is easy to use. The maps associated with the state checklist have not been updated since 2004. The site also has details on how to prepare and submit vouchers. It's easy, low tech, and important. A voucher is valuable only if it is properly prepared and has the correct information associated with it.

The value of vouchers
Aside from documenting current distribution, vouchers can help clarify or define species limits and taxonomy; be used in toxicology, genetic, and biochemical studies; and track species composition over time. An excellent overview, The role of voucher specimens in validating faunistic and ecological research, was published by the Biological Survey of Canada. Please read it.

We hope this provides the backstory to our reluctance to always positively ID photos, and our frequent encouragement of catching odes to identify them and, if needed, voucher them.

[1] Donnelly, N. 2006. Rediscovery of Intergrade Epitheca in Southern Indiana. Argia 18(2):12-13.

[2] O'Brien, M. 2004. Epitheca costalis (Stripe-winged Baskettail) in Michigan: Update.
Williamsonia 8(3):1-2. (PDF)

[3] Donnelly, T.W. 1991. Current problems in Sympetrum and Libellula (a.k.a. Plathemis).
Argia 3(4): 8-12.

[4] Craves, J. 2005. Canada Darner with an unusual thorax pattern.
Williamsonia 9(1):1.

4 comments:

KaHolly said...

Very well stated. Thanks for so much information and encouragement. ~karen

Mark said...

That is about the best summary I have read about why vouchers are important! And not because you mention my name.

Anonymous said...

Many species can only be identified by close examination in the hand, fair enough. But where are the resources to do so?

I have been meaning to contribute to the Minnesota Odonata Survey Project (MOSP) for a few years now but all I have is a box of unidentified specimens and a notebook full of well, maybe I saw this.

A taxonomic key would be useful. As would access to collections. We amateurs are not scared of reference materials. The University of Minnesota was less than helpful and field guides just don't cut it.

Nannothemis said...

Good point. As we mentioned, most of the newer field guides to have diagrams to the male claspers of many groups of odes -- bluets, darners, spreadwings, and gomphids. A copy of these diagrams in your pocket will SUBSTANTIALLY increase the number of odes you'll be able to identify in hand. We recommend some guides with good diagrams in our Amazon store (http://bit.ly/bXgLyP).

Our favorite book remains The Dragonflies and Damselflies of Ohio by Glotzhober & McShaffrey (http://bit.ly/bbIzot). It should work well for you for many MN species. The keys are based on those that are used by most experts, The Dragonflies of North America (http://bit.ly/dun2K0) and the Damselflies of North America (http://bit.ly/9BPzZb). They are pricey and harder to find, but worth the investment if you're going to get really serious.

It's my understanding that the MN ode survey (like ours in MI) will accept unidentified specimens so long as specific date and location data is attached. It takes longer for feedback, but you still get to make a significant contribution.

If you have problems in this regard, write to us directly and we'll see if we can grease some wheels.