522 Observations on Habits and Parasites of Common Flies 
observer was somewhat hindered by want of appliances, but he states 
that the flies died while the pseudo-scorpions remained on the legs and 
“that after the flies’ death the creatures travelled along the legs to the 
body, and finally drew the insects under the leaves to suck out their 
juices.” 
Experiments of this kind should be repeated, under more natural 
conditions, the pseudo-scorpions and flies being supplied with their 
accustomed food. 
(c) Another view is that the chelifers resort to flies in order to feed 
on the parasitic mites (Hickson, 1905; Pocock, 1905). Though chelifers 
may resort to beetles for this purpose, it seems clear that this is not the 
reason for their attaching themselves to flies, since many of the flies 
to which chelifers cling have no visible mites on them. Very small 
hypopial nymphs are said, however, to be frequent on flies, and would 
pass unnoticed unless carefully looked for. 
( d ) The dispersal hypothesis, which has the support of many 
observers, claims that the chelifers cling intentionally to flies in order 
to be transported from one feeding ground to another. Others, however, 
think that the seizure of the fly’s leg is either accidental, the chelifer 
mistaking it for some small insect suitable for food, or through irritation 
at being disturbed. 
“ The attachment, whether intended or accidental, obviously serves 
for dispersal; but it is probable that it is not a means of dispersal 
only, the phenomena having, almost certainly, a further significance.” 
The writer carefully observed some of the infested flies he caught, 
and in view of the various hypotheses, which have been discussed, these 
observations may be of some interest. The chelifer always grasped the 
fly’s leg by one claw and was never seen to make any attempt to seize 
it with both, or to climb up the limb towards the body. The house-fly 
with three chelifers attached to it caught on Sept. 7 was placed in a 
glass box. By the next day two of the arachnids had relaxed their 
hold, and were crawling about the box. They never made any attempt 
to seize the fly again although the fly frequently walked over them. 
The other remained clinging to the fly till the insect was killed on the 
9th (48 hours). The house-fly caught on Oct. 3 with a chelifer attached 
to the base of its tarsus was kept in a glass box for 4 days. During 
the whole of this time (90 hours) the chelifer remained attached in the 
same position. On the evening of the 4th day, however, it dropped off , 
but soon reattached itself to the back of the fly near the junction of 
the thorax and abdomen. After a time the fly managed to remove it 
