Sexing frogs can be a difficult task due to the fact that most differences in gender vary according to the frog species. You can use a frog's colours, size and special body features to determine if a frog is male or female, according to the differences determined for the frog species.
Identify the species of frog. Knowing the species of the frogs you seek to sex allows you to look at the distinct differences between male and female frogs of that particular species.
Examine the frog’s front legs and fingers. In species such as the wood frog, the male has a permanent, rough and darkened patch on the thumb, which he uses to grasp the female during mating. Other species of male frogs only develop these rough pads during breeding season.
Listen for frog calls. In many species of frogs, only the males make any sound. These calls attract females during mating season. However, exceptions to this rule exist because in a few species of frogs, only the females make calls.
Look at the underside of the frog's throat. In many species, the boy and girl frogs differ in the throat colouration. These colours vary greatly, and knowing the species of frog you have allows you to easily identify males and females according to throat colours.
Look at the size of the frog. If you have two frogs of the same species and of a similar age, the smaller of the two frogs is generally the male of the species. Commonly the male frog is several times smaller than the female of the same species, though in some species the smallest of the two is the female.
Observe the frogs during mating. During mating, one or several small, male frogs collect on the larger female's back to fertilise eggs. Due to the male's small size in comparison to the female, you often see more than one male attempting to mate with one female.
Take the frog to a local pet store that deals with frogs. Ask the staff at the pet store to show you the differences between the boy and girl frogs of a species. If the staff member does not know the differences, you can attempt to locate another staff member than can assist you.
Call a local veterinarian who deals with amphibians. Tell him the species of frog you have, and he can offer distinctive characteristics between the males and females of that species.