Specimen condition and preparation. Clean specimens (greasy specimens are quite common in collections) with wings slightly open are needed to view the dorsal surface of the abdomen. At least one antenna and one leg of each pair must be present and complete.
It is often important to know the sex of the specimen to be keyed. Males and females are easily separated. The main sexual differences differences for all species are on the hind leg and the abdomen.
Male identification does not require dissection; female identification usually does. The apical section of the ovipositor sheath should be removed to see the apical half of the ovipositor. To expose the apical half of the ovipositor, insert an insect pin near the apex of the sheath between the ovipositor and the apical section of the sheath. It should break at the junction of the basal and apical sections. Alternatively, the complete ovipositor may easily be pulled out of its sheaths either after relaxing a dried specimen for about 36 hours in a very humid atmosphere (in a closed container) or immediately after pinning an alcohol preserved specimen. To see most or all the ovipositor of a relaxed or recently mounted alcohol preserved specimen, insert an insect pin between the ovipositor and the apical section of the sheath and gently slide the pin toward the base of the sheath. This will force the ovipositor out of the sheath and the apical section of the sheath will return to its normal position (the sheath will not break). Ensure that the ovipositor remains out of the sheath. Use a fine paintbrush dipped in 95% alcohol to remove any dirt from the ovipositor. The specimen is now ready to be keyed.
Lighting. The light source is important. The best light is diffused light. Diffused light could come directly from a daylight fluorescent light (13 watts is usually satisfactory) or is produced with a semi-opaque plastic between the light source and the specimen. The best diffusion is achieved when the plastic is less than 20 mm from the specimen. This type of lighting eliminates all or most glare from smooth surfaces or those with metallic reflections. Such lighting makes structural features very clear and has been used throughout our work as illustrated in the numerous figures. We use a small (5 by 7 cm) piece of transparent plastic (Mylar) placed vertically on a base of modeling clay about 20 mm from the specimen to provide a sharp, glare-free image, of ovipositor pits for example. A dissecting microscope with a magnifying range of 40–60 times is recommended to view a structure clearly.
Key construction. Each couplet is arranged in contrasting pairs of statements labeled, respectively, with upper and lower case letters. Each statement almost always describes one feature of a character. So, different expressions of the same character would be found, for example, in couplet 8A and 8a. Information that is not compared in the alternate part of the couplet is given between brackets. Clarification notes are given in parentheses. Almost all statements of each couplet are illustrated. Each figure in addition to a number has the statement code: a capital or a lower case letter. Two figures with the same statement code may be mentioned to show a range of variation for a character. The illustration shown is not necessarily that of the species named, but is a similar expression of the character to be observed. In these cases, other structures in the figure should be ignored as they do not represent the species keyed. Plates of figures are organized so that the contrasting statements of each character are adjacent to one another. Arrows and morphological terms are added for clarity.
Field guide to Siricidae of North America. Schiff et al. (2006) published a key to genera and species of the North American Siricidae. Their excellent illustrations should help anyone without a reference collection trying to identify a specimen. However, the names of many habitus images need to be revised. We refer to such habitus images under each species of our revision. For other modifications associated with images see Appendix 2.