European centipedes are usually brown or yellowish in colour but tropical scolopendromorphs show a remarkable range of bright colours, Ethmostigmus trigonopodus (Leach) being almost black with orange legs, Rhysida nuda togoenis deep violet and Asanda sokotrana Pocock red.

The purple pigment of Lithobius

Plateau (1878) noted, that the mandibular glands of Lithobius forficatus were often violet and Duboscq (1898) noted that the connective tissue contained a violet pigment and the blood of this species had a violet tint. The pigment is water soluble and present in granular form in asteroid cells underlying the epidermis and following the tracheal system (Needham, 1960). When Lithobius forficatus is dissected the intensity of the violet colour increases implying that in vivo the pigment is in a colourless, reduced form (Needham, 1945). The reduced pigment is pale yellow. It is rapidly and reversibly reduced by chemical reducing agents, including ascorbic acid, but remains oxidised down to very low oxygen tensions (Needham, 1958).

The purified pigment has a molecular weight of about 4000 and contains no detectable copper so that the chromophore is not a copper-protein or biuret type compound as Needham (1960) had suggested. The absorption spectrum, the nature of the redox and pH colour changes and some other factors suggest that the pigment may be a hydroxyquinone (Bannister & Needham, 1971). For a quinone to be so soluble in water and so insoluble in all lipid solvents tested, as is this pigment, it would have to be very firmly bound to some very hydrophilic conjugant.