Why Do Green Lizards Have A Blue Head?

A male western green lizard (Lacerta bilineata) shows off its bright blue face (photo: Malcantone, Ticino, Switzerland) 

Green lizards only have blue heads during mating season from April to June; the colors are particularly intense during this period in males, whose faces and throats get bright blue or turquoise. This applies to the western green lizard (Lacerta bilineata) and the European green lizard (Lacerta viridis) as well as the Iberian emerald lizard aka Schreiber's green lizard (Lacerta schreiberi).

A male western green lizard sticks its bright blue head out from a pile of straw (photo: Malcantone, Ticino, CH)

The striking color signals the females - as well as potential rivals in their territory - their strength, health, and dominance. But the females of these beautiful reptiles also become more colorful in spring and are in some cases almost as brilliantly colored as the males, even if this is the exception rather than the rule. Normally, females are much less conspicuously colored than male lizards.

Male and female western green lizards during mating season: both sexes are intensely colored and show a blue (m) and a turquoise (f) face, respectively (photo: Malcantone, Ticino, CH)

The flashy coloration of green lizards becomes visible with the first molt after they reemerge from their winter shelters (as ectotherms, green lizards "brumate" during the colder period from around October to March - which means they stop eating, slow their heartbeat and rest in hiding places that are insulated from the cold).

Outside of mating season, both sexes are predominantly green in color and thus well camouflaged. Another species of green lizard, the Balkan green lizard (Lacerta trilineata), usually remains green throughout the year and does not develop a bright blue head during mating season.

Male western green lizard outside mating season in August; the head is not blue, and the animal is well camouflaged among the leaves of a shrub (photo: Malcantone, Ticino, CH)

Female western green lizard outside mating season in August (photo: Malcantone, Ticino, CH).

If you would like to see a direct comparison of the colors of the same individuals during and outside mating season, you can find more photos on this topic here.

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