Identification guide to the ant (Hymenoptera: Formicidae) genera of the Midwest of the USA

Introduction and how to use the keys

How to prepare specimens

Why use color images

Image-based identification guide

Glossary of terms used in keys

Introduction and how to use the keys

     This image-based identification guide should enable the user to identify any ant collected in the Midwest to the genus level. All keys used in this identification guide are modified from one or more sources (e.g. Creighton 1950, Wheeler & Wheeler 1963, 1986, Holldobler & Wilson 1990, Bolton 1994, see the literature cited for complete list)

     The keys used in the guide are dichotomous. At every point, the user must decide which of two statements (together forming a couplet) best describes the specimen being examined. If the correct decisions are made, the key will lead through couplets to the correct identification.

     For example, the first couplet for the key to the genera of the subfamily Myrmicinae looks like:
1.Antennae with ten or less segments (Fig. 55). ...2.
    Antennae with more than ten segments (Fig. 56). ...3.

     If the ant being examined has 10 or less antennal segments, you would follow the link to couplet 2. If the ant is blessed with 11 or more antennal segments, then you would follow the link to couplet 3. Whenever possible, images showing the characters used in the key are displayed in the top half of the page. So, in the example above Figure 55 shows a 10 segmented antenna and Figure 56 shows an 11 segmented antenna. A list of the taxa remaining in the key (all 17 of the Myrmicine genera found in the Midwest in the example above) is shown to the left so that the user has some idea what possibilities are left. Also, each name in the list is linked to a page giving general information and side and front view images of the taxa (when possible) which can give at least a general idea what the taxa should look like.

     In some cases, more than one diagnostic separatory character is presented in the couplets. The first character is generally the most useful or easily seen. No specimen should fit both halves (or 'lugs') of the couplet - the characters used in keys are supposed to easily and efficiently separate the taxa for which the keys are made. If you cannot make a clearcut decision (as is often the case, especially when the keys are unfamiliar), proceed through each of the two paths until you reach an endpoint. Hopefully it will be obvious (from the characters used in the key and from the image database) which of the two possible identities is correct.

     As an identification aide, when a taxa is reached in the keys, the Midwestern states in which the taxa has been collected are reported in parentheses directly below each lug. For example, couplet 11 of the key to the genera of the subfamily Myrmicinae looks like:
11.Propodeum armed with spines.
(collected in all Midwestern states)
   Propodeum not armed with spines.
(one species, M. mutica, collected in western North Dakota)

     So, if you got to couplet 11 and for some reason you were unsure whether your specimen had spines, you could be nearly certain that you had a species of Myrmica unless you collected your specimen in western North Dakota (or outside of the Midwest).

     As a further aide, taxa which are very rare (defined as having been collected in 5 or less counties throughout the Midwestern states surveyed) are marked with a pound symbol (#). Similarly, taxa which have been collected in 6-11 counties are marked with a double-pound symbol (##). Taxa marked as such are unlikely to be found with casual collecting and much of the time you can safely skip over these taxa.

     And finally, because the focus of the present study has been on the ants of Minnesota, ant taxa which have not been collected in Minnesota are marked with an asterisk (*).

Why use color images?

     Identifying ants using dichotomous keys can be very troubling. The difficulty lies in the inability of words alone to easily describe the specific morphological characters that allow for the separation of taxa. As a result (and to the exasperation of beginners), precise morphological terminology must be used. Luckily, drawings or images can be used to demonstrate the characters described in keys.

     In fact, genera often have distinct different overall appearances and with practice can be identified without a key at all. In this way, the keys to genera in Holldobler & Wilson (1990) have profile line drawings of all the genera that are extremely useful. Wheeler & Wheeler (1963, 1986) go a step further and use line drawings of the characters used in their keys to the ants of North Dakota. Bolton (1994) uses profile and full face scanning electron microscope (SEM) photographs, as well as SEM photographs showing close-ups of diagnostic characters, in his guide to the ant genera of the world.

     Although color images cannot show the detail of line drawings or SEM photographs, there are benefits to using color images: 1). the color images used in this identification guide have been produced using video equipment attached directly to a compound microscope -- precisely the type of instrument that will most likely be used by those attempting to use this (or any) key. What you see in this key is what you see when examining the actual specimen being identified. 2). Although color is usually not a good diagnostic character because of its variability (Creighton 1950, Wheeler & Wheeler 1963), it is useful to have some sort of idea of the color possibilities. 3). And most importantly, color images are much easier to produce then either line drawings or SEM photographs.

Please send any questions or comments regarding these pages to Tim Linksvayer (