492 Observations on Habits and Parasites of Common Flies 
the two traps were equally attractive. In November trap IV became 
the most attractive. 
Traps II (excrement) and V (animal matter) in shady situations. 
These two traps were in similar situations, but whereas trap II was an 
open net trap, trap V was a dark receptacle, and therefore less likely 
to attract flies. Up to July trap II was the most attractive, but in 
August, October and November more flies visited trap V. 
Traps III (excrement) and VI (animal matter) both dark receptacles 
in open situations. Up to September trap III, which was protected 
from winds and the afternoon sun, was the most attractive, great 
numbers occasionally visiting it on very hot and windy days (p. 499), 
but in October and November a change occurred, large numbers of flies 
visiting trap VI, and none going to trap III. This was probably due 
to the fact that trap VI was more influenced by the heat of the sun 
than trap III. Moreover a large proportion of the flies caught during 
these months were old blow-flies attracted to animal matter in order 
to lay their eggs. 
It would appear from these observations that early in the season 
when flies are emerging excrement is more attractive than decomposing 
animal matter 1 , but late in the season, when recently emerged specimens 
are less common, animal remains are the more attractive, especially to 
the numerous females ready to deposit eggs. 
Several experiments were made in order to ascertain how long 
masses of excrement retained their attraction for flies, traps being 
placed over fresh masses, and the flies caught and examined daily. In 
sunny places the attractive power was greatest on the first day, slightly 
less on the second, and was much diminished on the third. Flies in 
small numbers continued to be attracted up to the seventh day in some 
experiments. In the shade flies were seldom attracted after the third 
day. 
That relatively fresh carcases are extremely attractive to flies of 
the genus Lucilia is shown by the following observation. The lacerated 
body of a recently killed bird was found covered with green-bottles 
in a country lane. The carcase was carried several hundred yards and 
then placed on the ground. Within a few minutes it was again covered 
with these flies although none of them were seen to be following. 
1 Between April 21 and May 2, 1916, 1294 flies, 462 (J and 832 $, visited a trap baited 
with excrement, and only 11 flies a trap baited with small carcases. Towards the end of 
May the latter trap became more attractive. 
