How to Use a Key

Keys are a tool to determine the probable identity of a specimen in hand. Keys are designed and used by scientists to ensure accurate identifications when a specimen is available. Keys work by using the presence or absence of "key" characteristics to eliminate one group or species after another until only one species remains. The Key on this website divides the country into three regions: Eastern United States includes all states east of the Mississippi River; Western United States includes all states west of the Mississippi River; and the Hawaiian Islands.

For example, in the Key to the geckos of the eastern United States, the first pair of alternatives asks whether the gecko has moveable eyelids or whether the eyes are covered by a fixed transparent covering. If you decide it has moveable eyelids, moving across the page tells you "not a gecko," and therefore your specimen is not included in the key. If the second alternative is true, you are directed to couplet #2. Couplet #2 asks whether the pupil is round, and if the gecko is diurnal, or whether the pupil is vertical, and the body color is brown or gray, not green. Try to match both parts of the alternatives, not just the first. After deciding, one choice directs you to couplet #3, the other to #4.

By continuing on, following the numbered couplets, you will eventually be left with only a single species. Keys are only part of the identification process. After getting this identification, go to the appropriate Species Profile. Compare your specimen to the photos and descriptions. Does it match closely? Check the geographic range given in the description. If the appearance and description match, and the gecko is from within the species' geographic range, it is likely that the identification is correct.

If you can't seem to find your gecko, there are several possibilities. You may have misread or misinterpreted one of the key characteristics, and followed the wrong alternative to a misidentification. (Pay close attention to the first question, which will help you determine if it is a gecko at all or another type of similar looking lizard.) Also, juvenile geckos often look different from adults. Occasionally, a particular gecko may be abnormal, different in color, pattern or even body shape from a typical member of its species. Finally, it is also possible, particularly if the gecko is an introduced species, that it may be a waif, transported out of its normal range by accident or deliberate release, or it may even be part of an unknown introduced colony or native population.