18 Mr. W. Spence on the Pulvilli of Flies. 
Ill. On the Pulvilli of Flies. By Wii11am Spence, Esq. 
E:RS., &c: 
[Read 6th March, 1843.] 
In a note at p. 261, vol. ii. of the new edition of our ‘“ Introduc- 
duction to Entomology,” on the pulvilli of the common house-fly, 
I have detailed the observations which led me to the conclusion, 
that if the hypothesis of Mr. Blackwall, which refers the power 
possessed by this insect of walking up polished vertical surfaces 
or horizontal ones with its back downwards, to the exudation of a 
glutinous secretion from the ends of the hairs of its pulvilli, be 
proved to be correct, it will probably be found that the process 
of rubbing its tarsi together, which it constantly exhibits, is not, 
as has been formerly supposed, one of mere general cleanliness, 
but a very important operation of its economy, destined to keep 
the ends of the hairs of its pulvilli free from every particle of 
dust or moisture which might impede their adhesive action. My 
attention, since leaving England for Italy, has been frequently 
directed to this subject; and all my observations confirm the 
probability of this supposition being well founded, not merely in 
the case of the house-fly, but of Dipterous and Hymenopterous 
insects generally, and of many Coleopterous species, a large pro- 
portion of which I have seen employ similar manceuvres, appa- 
rently for a similar purpose. It would be tedious, as the results 
are so uniform, to give any detailed account of these observations, 
but I may mention one of them, which struck me more forcibly 
than the rest. I have repeatedly seen flies, after rubbing together 
their two fore tarsi and pulvilli, put down on the surface on which 
they were standing, first one of the pulvilli, and then the other, 
and pull at each, as if trying if they would adhere properly: ap- 
parently finding from the trial that they would not, again briskly 
have recourse to the former curry-combing process, repeating 
these alternate brushings and trials five or six times, and for the 
space of full two minutes, until having seemingly ascertained that 
the pulvilli were completely cleaned, and in a fit state to act, they 
walked or flew away. I do not give this fact as in itself of much 
weight ; but taken in combination with those I had before ob- 
served and recorded in the note above referred to, it tends to 
confirm the supposition there started, as the mere cleansing of 
the tarsi themselves from dust could scarcely have required so 
long a process, and interrupted by so many apparent trials of its 
effect on the pulvilli. My main reason, however, for bringing it 
