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A POSSIBLE FUNCTION OF THE HAIRS IN CERTAIN 
LEPIDOPTEROUS LARVAE. 
GEO. B. WALSH, B.SC. 
Many species of larvae in certain families of the Lepidoptera, 
e.g. Arctiadcz, OcneriadcB , Lasiocampidce , are noteworthy for 
their more or less dense covering of hairs. In all probability 
these hairs serve a variety of functions : in some cases, e.g. 
Porthesia chrysorrhoea Linn., Euproctis phceorrhoea Don., 
they are protective in function owing to their urticating 
properties ; in some others, e.g. Lymantria dispar Linn., 
Orgyia antiqua Linn., the present writer has suggested (‘ The 
Origin and Distribution of the Coast Coleoptera of the British 
Isles,' Ent. Mon. Mag., Vol. LXII, 1926, p. 228) that they 
function in assisting dispersal by wind immediately after 
eclosion from the egg. 
It would seem probable, however, on a priori grounds that 
the presence of numerous hairs on a larvae would materially 
reduce the rate of loss of water from the body just as hairs on 
certain plants, e.g. Tussilago, Verbascum, reduce the rate of 
transpiration from a leaf -surface ; if this be true, it will 
presumably be most effective in the case of hairs lying along 
the spiracles. 
To test this hypothesis, experiments were carried out 
last year (1932) with larvae of Arctia caja Linn, and Diacrisia 
lubricipeda Linn. To remove the hairs as completely as 
possible, particularly along the spiracular lines, the larvae to 
be tested were clipped with fine scissors, care being taken not 
to cut so closely as to cause obvious bleeding. The larvae 
were then placed in an empty tin for at least 24 hours till the 
intestine was emptied of food. A number were then weighed 
on a chemical balance. These were then placed in a desiccator 
containing calcium chloride as drying agent, the larvae being 
removed from contact with it by a piece of wire gauze. The 
idea of this was to ensure exactly parallel conditions for the 
shorn larvae and their unshorn controls, to increase, if possible, 
the rate of transpiration, or on the other hand to prevent its 
possible check by a damp atmosphere. After a period varying 
from 10 J to 24 hours, the larvae were removed and weighed 
again. As a control the experiment was carried out at the 
same time and in the same way with a number of unshorn 
larvae. In the case of Arctia caja, the experiment was repeated 
with other larvae in order to check the results obtained. 
During later consideration of these results, it seemed 
possible, however, that the excess of loss from the shorn 
larvae might be due to a slight degree of bleeding from the 
cut hairs. It was too late then to repeat the experiment in 
1933 July 1 
