[Thaumetopoea pityocampa caterpillar and man. Morphology of its venom apparatus. Epidemiological investigation (author's transl)].

The combination of a mechanical phenomenon (penetration of the hair) and a chemical phenomenon (discharge of a toxic substance) accounts for the pathological symptomatalogy induced by the processional pine caterpillar. Epidemiological study has pin-pointed the regions infested by the pine caterpillar and has described in detail the dermatitis inflicted by this caterpillar with special emphasis on the frequency of ocular lesions. Also, a close correlation was noted between the geographical density of the populations of Thaumetopoea pityocampa Schiff and the geographical density of the clinical cases recorded. Skin tests have confirmed that the urticant substance is histamino-liberating. A morphological study of the urticant apparatus of this caterpillar ("mirror" and urticant hairs) was undertaken with the scanning electron microscope. The progressive coming into place of the bristles on the cuticular pads of the "mirror" was followed during the last three larval stages (L3, L4 et L5). The urticant hair, hollow on the inside, carries pointed spikes directed towards its distal end. There is no hole or pores on the hair and the necessity to grind the bristles in order to extract the urticant substance leads us to believe that the hair is really a bulb which must be broken, for example in the skin, in order to release its urticant substance (histamino-liberating).