Fig. 2. Four successive frames from high-speed video relate closing wing positions to the pulse train of Arachnoscelis n. sp. Insect faces to the right. The anal margin of the overlying (file-bearing) left wing is marked by a red arrow; coloured broken lines match picture and wing velocities to the oscillogram. The wings develop a velocity before each production of a pulse (calculated CWV below frame) and then become almost still over the interval of pulse generation; scale bar, 5 ms. (A) CWV is at 7.1 mm s^-1; scale bar, 0.5 mm. (B) During the production of the first pulse (compare A and B) there is no detectable movement of the wings and the CWV drops to zero. (C) The wings close further, giving a CWV of 14.5 mm s^-1. (D) Next pulse is produced, again without measurable displacement of the wings. Association of motionless wing intervals with sound pulses implies scraper movement.