**Methene** do not exist in nature. This is because the **alkene** family have the general formula **C** _{n }**H** _{2n }where n is a natural number(which starts from 1). If we substitute 1 in place of n, then we get the formula CH_{2}. CH_{2} has no independent existence, as the tetravalent nature of carbon is being violated.To have a double bond you need at least two atoms, so ethene is the smallest possible alkene.