G. S. Graiiam-Smitii 355 
In September 1916 a large number of M. corvina confined in another cage 
outside all died of the disease. 
In June 1918 Keilin observed great numbers of S. slercoraria dead of the 
disease clinging to nettles in a meadow near Cambridge. 
MITES. 
The Gamasid mites previously described (1916, p. 511) were very common 
on animal remains and faecal matter containing fly larvae during 1916 and 
1917, and their habits were more closely observed. They were often seen 
to attack and kill freshly hatched larvae. They also feed on the eggs of flies, 
sucking out their contents and rejecting the shrivelled integument. These 
mites occur in very great numbers, and must cause the destruction of great 
numbers of eggs and young larvae. 
Red mites were seen attached to the legs and bodies of Lucilia and //. 
dentines in July and August in both 1916 and 1917. 
BEETLES. 
Beetles of various species seriously interfered with several experiments, 
and are probably beneficial by destroying both larvae and pupae under 
natural conditions. In one experiment a jar containing fly puparia was left 
exposed in the open. On examining this jar a few days later 22 specimens of 
Creophilus maxillosus were discovered in it, and almost all the puparia were 
found to be torn open and destroyed. This beetle is a strong flier, and is readily 
attracted to all decomposing materials. 
Two other species ( Necrophorus humator, Hister cadaverrinus ), very common 
in decomposing animal matter, seem to be destructive to larvae and pupae. 
Even buried puparia may be attacked, for in another experiment a large 
number of puparia buried at a depth of 2 inches were found torn in pieces. 
One of the beetles (Pterostichus madidus) attacking these puparia was closely 
observed for some time. It carried off a puparium holding it in its mandibles 
by one end. The puparium was taken from it, and placed on the ground a 
short distance away. The beetle immediately searched for it, found it, and 
took it up and finally disappeared with it into a crevice in the ground. 
Dr G. W. Nicholson very kindly identified several species of beetles sub¬ 
mitted to him. 
PARASITES ATTACKING FLY LARVAE OR PUPARIA. 
Since the autumn of 1915 fly larvae and puparia collected at various times 
have been kept under observation in separate receptacles, with notes recording 
their origin and date of collection. From these naturally infected puparia 
members of the five most important families of the Hymenoptera parasitica 
or Terebrantia, the Cynipidae, Proctotrypidae , Ckalcididae , Ichneumonidae and 
Braconidae, have been obtained. 
