A doctoral thesis by Maria Febrer of the University of the Balearic Islands has examined the impact of invasive snakes in Mallorca and the Balearics. She has studied five species, two of which - the viperine water snake and the false smooth snake - have been in the Balearics for many centuries and are not considered to be invasive, albeit that they are not common to all the islands; only Mallorca and Menorca.
The other three should be classified as invasive. The ladder snake has existed in Menorca for many years but has recently been found on the other islands. The horseshoe whip snake is invasive in Mallorca and Ibiza/Formentera but hasn't been found in Menorca. A similar situation applies to the green snake.
Febrer explains that the green snake is a recent introduction in Mallorca and that it can have a serious impact in sensitive areas such as Albufera. It eats small mammals, birds and reptiles, but it hasn't yet been officially declared invasive. And nor are the ladder and horseshoe snakes classified as invasive.
She argues that it is essential that they are given this classification in order to take far greater control of their potential import and to take measures to eradicate them. Febrer stresses that these snakes can cause "ecological disasters".
A key measure she recommends is all-year controls of trees that are imported. Snakes, during their hibernation, hide in the trees, but this hibernation, she argues, is not "mathematical". It can change depending on weather conditions.