Observations on the Development of Lucilia Sericata (Mg.) Eggs in Sheep Fleeces

Abstract

1. Comparative determinations of fleece atmosphere R.H. using cobalt-chloride papers and paper hygrometers showed that the former were reliable, although their use was infject to a limited humidity range (40-70 % R.H.). Determinations made by means of wool samples were found to be infject to large positive errors, since the wool near the skin did not appear to be in equilibrium with the fleece atmosphere. 2. Measurements of fleece R.H . by cobalt-chloride papers on twenty-eight sheep of various breeds showed that the R.H. varied considerably from day to day in individual sheep, and in different sheep at the same time. The common condition was one of low R.H., unsuitable for the development of blowfly eggs. 3. R.H. measurements and a study of the fate of L. sericata egg batches placed in fleeces showed, however, that conditions suitable for development were occasionally experienced in these sheep. Humidities high enough for hatching were more rarely found. 4. Rapid secretion of watery material by the skin (sweating), leading to suitable humidity conditions for strike, was detected. The various sheep used showed great differences in sweating rates, the most rapid sweating being found in two Down Cross lambs where, at one period, the limiting factor for strike must have been that the blowflies were not attracted to them.