How to Identify a Moth
This website depends on accurately identified species records, but we are primarily interested in figuring out distributions, habitat associations, and conservation status based on those records. There are several other sources that are devoted more to identification and we recommend that they be consulted first in order to come up with at least an initial identification (a preliminary species name is, in fact, required to submit a record). Once an initial identification is made, however, you may then want to consult the Species Accounts in our website for additional information on the field marks and other information that we ourselves use as standards for diagnosing a particular species. Unless otherwise stated, the terms in the species accounts that are used to describe the morphology, coloration and patterning of a species are those seen when viewing the specimen either from above or from the sides. For example, a description of the coloration of the forewing is one that applies to the upper surface of the wing and not the lower surface.
FIELD GUIDES
Two Peterson Field Guides have been published for the moths of the eastern United States, both following the same format as the original Field Guide to the Birds by RT Peterson. Identification involves matching species (or photos) to pictures in the book, with supplemental information provided on distinguishing field marks (i.e., the visual or behavioral cues that can be made out in the field), habitat, range, and seasonality.
Charles Covell’s A Field Guide to the Moths of the Eastern United States was published in 1984 (see References for publication information). Although it went out of print for a few years, it has been republished by the Virginia Museum of Natural History. It covers 1,300 species belonging to 59 families in detail (but still just a small fraction of the total number of species in our area). The taxonomy follows the 1983 Checklist of the Lepidoptera of America North of Mexico by Hodges et al., which was (and still is) the most authoritative list available, but which is now out of date for many taxa, with new species having been described, changes having been made to generic names, and some families merged or split (the newer version contains some of these revisions). The plates – some of which are in black-and-white – include photographs of spread specimens, having the advantage of showing the hindwings and abdomen, which for many species possess features that are critical for their identification. No maps are provided and the range information – which was fairly general to begin with -- is now out of date, with many species now recorded in North Carolina not indicated as occurring in our state. An excellent glossary of technical terms is included, along with detailed illustrations of morphological features.
The Peterson Field Guide to Moths of Southeastern North America by Seabrooke Leckie and David Beadle, published in 2018, represents a different approach to portraying moths: instead of spread specimens, it provides photos of living moths, almost all with wings folded in the natural resting posture. This has the advantage of showing the species as they are most likely observed by moth watchers or photographers, and includes postural information that may be highly characteristic of particular species. The drawback, however, is that useful information provided by the hindwing and abdomen is often hidden from view (and not mentioned in the text). All photos are large and located opposite the text for a given species, another advantage over the older field guide. The taxonomy is much more up-to-date than Covell’s, following major changes to the Noctuoidea by Lafontaine and Schmidt. With its aim of serving the interests of moth observers or photographers, the finer morphological details and technical descriptions of greater interest to collectors are not included here to any great extent, although a glossary is provided and illustrations given that cover at least the wing patterns and a few of the more easily visible morphological structures.
Caterpillars of Eastern North America by David Wagner, published in 2005, combines excellent photographs and technical descriptions that cover the larvae of most groups of macro-moths that occur in our area, plus a few of the micros (e.g., the Limacodids). Although there are more comprehensive treatments for individual families (see Technical Literature below), this is the single best source of information for moth caterpillars, covering the widest range of families and species, and is the most easily available to the public.
WEBSITES
Compared to birds, butterflies, mammals, and other groups that have been very successfully treated in field guides, there are simply too many species, too many variations within species, and too many closely similar species among moths to be handled by a single book (especially one small enough to be taken out into the field). While field guides are still good places to start, especially to identify a moth to family, subfamily, or genus, internet websites are able to handle more species, provide more information per species, and can be updated more rapidly. There are now a number of websites that specialize in providing identifications for moths, three of which are particularly useful for identifying a species from scratch.
The Moth Photographer’s Group (MPG) Website (http://mothphotographersgroup.msstate.edu/ ) aims at providing photographs, distribution maps, and flight charts for all North American species of moths, both micros and macros. The taxonomy is the most up-to-date of any current source and multiple photos are usually included, capturing some of the range of variation found in a given species. Caterpillars are also shown in some cases, and there is also library of genitalic slides for some species. For identifying an unknown moth, the website can be used like a field guide, where a moth or a photo is matched against a picture in the website. Since there are thousands of moths to scan through, MPG makes the process easier by providing a series of plates of both spread specimens and live moths. These are sorted taxonomically and are easiest to use if you already have some idea about what family the moth might belong to.
BugGuide
(http://bugguide.net/node/view/15740) is a key resource for identifying all terrestrial arthropods. Its coverage of moth species is similar to that of MPG and makes use of the same taxonomic sources. Although its distribution maps are less detailed than MPG’s, BugGuide otherwise provides a lot more information for each species (not all of which is yet filled in for any given species). Like MPG, it also has a scanning function (Browse) that allows fairly rapid comparison between the specimen to be identified and potentially matching species. In BugGuide’s version, browsing for matches can be done hierarchically, starting at any taxonomic level between Superfamily and Genus, and then successively narrowing the choices. For example, if you know that your moth belongs to the Inchworm family – Geometridae – you can start at that level and narrow it down first to subfamily, then to tribe, then to genus, and finally to a particular species. This approach is not only useful for someone who knows little, if anything, about moth taxonomy, but also provides an efficient way of searching for someone with more experience, who can start the process much lower down in the hierarchy (the authors of this website make frequent use of this service).
Where no apparent match can be made through this process, BugGuide also offers to identify photos of unknown species (see http://bugguide.net/node/view/6/bgimage?from=24). This is a free service and is done via collaboration with BugGuide’s existing members (joining BugGuide is also free). MPG offers a similar service (see http://mothphotographersgroup.msstate.edu/Submit.shtml), but they recommend that BugGuide be consulted first.
Butterflies and Moths of North America (BAMONA) http://www.butterfliesandmoths.org/ aims to provide photos and life-history information on all North American Lepidoptera. Like MPG and BugGuide, it offers a field guide approach to identifying species, again providing a way to scan through a number of higher level categories, narrowing the search ultimately down to just a single species. Photos can also be submitted for identification by regional experts (see http://www.butterfliesandmoths.org/identify).
Other Websites
A growing number of other websites exist that provide identified images of moths. One that is general in its coverage is:
- Barcode of Life Database (BOLD) (http://www.boldsystems.org/) -- provides photos of species that have been submitted for genetic analysis
Several websites are devoted to particular taxonomic groups, including the following that specialize on micro-moths:
- Tortricid.net, by Todd Gilligan (http://www.tortricidae.com/default.asp) -- covers the Tortricidae of the world; includes photographs of pinned specimens
- Pterophoridae of North America, by Deborah Matthews (http://www.plumemoth.com) – contains a checklist for North American species of Plume Moths; has photographs of some species and links to other webpages; provides an extensive bibliography for this group
- Microleps.org, by Terry Harrison (http://microleps.org/index.html) – contains extensive information on microlepidoptera, with annotated photos provided for a large number of species but concentrates on those found in Illinois
Websites that cover the moth fauna of individual states include the following for our neighboring states:
- Georgia Lepidoptera, by James Adams (http://www.daltonstate.edu/galeps/) – includes both moths and butterflies; provides a checklist of species that have been found in Georgia or that could possibly occur there; photographs are given for many of the species
- South Carolina Moths Searchable Checklist, by John Snyder (http://insect.furman.edu/sc-moths/) – contains a complete checklist of moths for South Carolina, with links to photographs and maps showing species’ distributions in the state
- Atlas of Rare Butterflies, Skippers, Moths, Dragonflies & Damselflies of Virginia, Virginia Natural Heritage Program (http://www.vararespecies.org) – covers rare species only but with important information regarding conservation
Among the many personal websites that contain moth photographs, the following concentrate on North Carolina species:
TECHNICAL LITERATURE
The field guide approach used by both the field guides and the websites – i.e., matching specimens (or photos of them) to photos – is all that is needed in many cases, but with so much individual variation and the large number of closely similar species found among moths, identification often requires measurements or the examination of smaller or more hidden morphological structures than are usually visible in photographs. In some cases, these features are described in the text of the field guides or websites but typically they are not mentioned at all. For our purposes, however, we need as precise identifications as possible, sometimes requiring the use of more detailed information available only in the underlying taxonomic literature, i.e., the same information used by taxonomists or collection curators to sort and assign specimens according to the features by which they were originally described.
For the more obscure groups – unfortunately including many of the micros – the original descriptions of a species may need to be sought out (although some, at least, are now available online; BugGuide is a good place to look for links). More useful are references that summarize the technical information at higher levels, e.g., genus or family. Most useful of all are those that provide dichotomous keys, based on diagnostic features that allow precise discriminations to be made between species.
The single most authoritative sources are the Moths of America North of Mexico (MONA) Series. These are monographs written by taxonomic experts on a particular group of moths that contain detailed descriptions and photographs, usually with at least some information also provided on larval host plants, habitats, and range. Although a number of these monographs have now been completed (see http://www.wedgefoundation.org/publications.asp), many groups – including some of the largest and most problematic (e.g., the Acronictas and Catocalas) – are still works in progress.
Another excellent source is Forbes’ Lepidoptera of New York and Neighboring States (in four volumes). Although much older than the MONA series and with much of its taxonomy and range information now out of date, Forbes’ books still provides some of the most useful technical descriptions and dichotomous keys for many of the moth species found in our area.
Other books and articles exist for individual families and genera, which are cited in our Species Accounts. Some of these references are available for purchase (some, like the MONA series, being fairly expensive) and most are available in university libraries or other large reference libraries (which can usually obtain them through inter-library loan if they do not have copies themselves). For the most part, the diagnostic information provided by these sources is what we rely on for identifying species and is summarized in the ID Comments section of the Species Accounts (still to be filled in for many species).
All of these references make use of specialized terms for describing markings and structures. Glossaries that describe these terms can be found in several of the works cited above, but two that are fairly accessible are Covell's Field Guide to the Moths (Covell, 1984) and the excellent online glossary included in the Pacific Northwest Moths website, available at: http://pnwmoths.biol.wwu.edu/about-moths/glossary/.
SPECIMEN-BASED IDENTIFICATION
A large number of moth species cannot be reliably identified using photographs alone: many of the key diagnostic features, as described in the technical literature mentioned above, can only be seen in collected specimens and usually require magnification and often dissection to get a clear view. If you are fortunate enough to live near a large reference collection, such as the Insect Museum at NC State University, direct comparison of a specimen to those identified in the collection offers one of the most traditional means of determining an unknown species. Specimens can also be taken to county extension service for identification or shipped to the NC State University Plant Disease and Insect Clinic (especially good for identifying caterpillars and their hostplants; see http://www.cals.ncsu.edu/plantpath/extension/clinic/).
Individual members of the North Carolina Biodiversity Project may also be willing to identify collected specimens, but usually only where a specimen would be particularly interesting taxonomically or where its occurrence would be new for either the state as a whole or for a particular region or habitat type (see Contacts for more information).
GENETIC ANALYSIS
DNA analysis has resulted in a revolution in taxonomic studies, revealing new relationships between species and in many cases leading to the discovery of new species that had not been previously identified based on morphology alone. Although these techniques are not yet generally available to anyone wishing to identify a particular unknown specimen, they are becoming more routinely used by taxonomists and have been employed in North Carolina in identifying and describing a number of species (see below).
In the Species Status comments included in the Species Account, we summarize the results of one particular method referred to as Genetic Barcoding (reference). This is a DNA sequencing technique that has become exceedingly popular over the past 10 years and has now been used to examine the taxonomic status of many groups of species, including a large number of moths. This method reads the sequence of nucleotides in a single mitochondrial gene (CO1) analogously to the way a barcode reader identifies a product label in a grocery store: each species has a unique sequence (with some minor variation among individuals and populations) that serves as a unique identifier, allowing comparisons to be made between an unknown specimen and previously sequenced species.
The CO1 gene (which codes for a portion of Cytochrome Oxidase, an enzyme used in energy production in the mitochondria) is present in all eucaryotes (animals, plants, fungi, and protista). Differences in the sequences between species reflects the accumulation of mutations that do not affect the function of the gene (i.e., are neutral in their effects). Such mutations are believed to occur randomly but to accumulate at a fairly fixed rate (similar to the radioactive decay of atoms). This provides a “molecular clock” for gauging how long two particular populations – once originally part of the same gene pool -- have been genetically isolated from one another: the longer the period of isolation, the greater the degree of their differences in their sequences for the CO1 gene.
Research has shown that a 2% difference in CO1 sequences is usually sufficient to identify two populations as distinct species, where individuals are no longer capable of interbreeding. This is true even where there may be little or no obvious differences in outward appearance (at least to a human observer). While that does not mean that species cannot become reproductively isolated over shorter intervals. For example, the black-winged Catocalas appear to be “good” species, showing at least some degree of reproductive isolation, even though they do not show a 2% difference in their CO1 sequences. Where a 2% difference is found, however, that usually indicates that a more careful search be made for differences in morphological, behavioral or ecological characters, revealing characters that allow for a conclusive recognition of new species
For the past 8 years we have been using DNA barcoding to investigate a number of questions concerning the variation of moth populations across North Carolina. We have looked at species where various polymorphic forms occur, where broods look very different, where broods occur at peculiar times, and where our populations are disjunct from the rest of the species’ range, all with the goal to determine whether they represent single species – as originally described – or are actually multiple sibling (and often cryptic) species. Followed by additional morphological, ecological and behavioral differences, these discoveries have led to the formal description of a number of new species, including the following: Morrisonia triangula (Sullivan and Adams, 2009), Rivula stepheni (Sullivan, 2009), Gondysia telma (Sullivan, 2010; Sullivan and Legrain, 2011), Palpita maritima (Sullivan and Solis, 2013), and Cherokeea attakullakulla (Quinter and Sullivan, 2014). Many more descriptions are currently in progress.
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