Human lice show photopositive behaviour to white light

Abstract

We studied the behavioural response of body lice and head lice to white light. We also evaluated the influence of starvation and the presence of other individuals on this response. Experiments were performed in a rectangular arena, half of which was illuminated and the other half kept in the dark. Two experiments were performed: in the first, a single louse was released into the arena for 60. min and the percentage of time spent in the illuminated half was recorded; in the second experiment, a group of lice was released and the number of insects in the illuminated half was recorded. The results showed that the average number of lice and time spent in the illuminated side of the arena was statistically higher than for the controls. Starvation did not influence the reaction of lice, but the number of insects in the illuminated area did increase with the size of the group. This study shows that human lice are photopositive towards white light and that this behaviour is not affected by the nutritional state of the insects. Moreover, it is enhanced by the presence of other lice.