The corn snake is a species of the rat snake family from the southeastern United States that can grow up to 5 feet long, but averages 3 to 4 feet when full-grown.
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Measuring Your Snake
Gently pick up your snake. Corn snakes are nonvenomous and generally don't bite, but a scared snake will be more difficult to measure. Once your snake is calm, place her on a flat surface alongside a ruler. Gently stretch the snake to be completely flat and record the distance from the snout to the tip of the tail. Call a friend or family member to help you -- having another set of hands on the task can make this measurement a lot easier.
Deducing Age from Length
A 1979 study of 220 corn snake specimens by Barnard, Hollinger and Romaine recorded lengths three times in the corn snakes' lives. At hatching, the corn snakes had an average length of 12.8 inches. Six months later, the snakes had grown to an average of 22.7 inches. The last measurement was taken when the snakes were one year old, and they averaged 35.1 inches. Measurements recorded after one year of age become progressively more variable and trying to figure out a snake longer and older than one year using this method is significantly less reliable. Use these measurements as a guideline to estimate the age of your snake.
Length vs. Food Intake
The core element of the study was to measure not only weight, length and age, but also food intake. Comparing variability across measurements and finding more reliable answers in the food intake portion of the experiment, the study states:
Thus, we conclude, that in general, the size of corn snakes depends more on food consumption than on the age of the specimen... It was also evident... that the amount of variation among individuals increased as the total amount of food consumed became greater.
The researchers also mention that in the wild, corn snakes will not feed as regularly as those in captivity, and thus their length is not as reliable a way to tell their age as it is for captive snakes on a controlled diet.