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A FEW NOTES ON MYRMECOPHILOUS SPIDERS. 
By Horace St. Joun K. DonistHorpe, F.Z.S. 
My friend Mr. O. Pickard-Cambridge, in some notes on new 
and rare British Arachnida in 1907, writes of Thyreosthenius 
biovatus, Cambr., as follows:—‘‘ Adult females were found by 
myself several years ago among débris and grass-stems in woods 
at Bloxworth, but have been overlooked until recently. Its most 
usual habitat appears to be in nests of Formica rufa; but besides 
the above I have specimens from other localities quite away 
from these nests. It does not seem to have been observed yet 
what the terms are on which it inhabits the ants’ nests, or 
whether these are used as breeding-places for the spiders or not, 
or whether they serve as shelter principally during the winter. 
The ant is large and protected by its coriaceous epidermis, while 
the spider is very minute and delicate, so that it seems difficult 
to imagine the latter making a prey of its hosts in any way, 
either in the egg or larva state; but of course there may be 
very minute insects in the ants’ nests which in the larva or 
perfect state would furnish food for the spiders. The subject of 
insects and, besides the spiders mentioned, various other species 
of Arachnids dwelling in ants’ nests is a very interesting one. 
It has been closely worked out by Mr. H. Donisthorpe, to whom 
I am indebted for many species of spiders he has found in nests 
of several species of ants. The greater majority of the spiders, 
however, found in ants’ nests are certainly, I think, simply there 
for purposes of warmth and shelter during the winter, and are 
mostly immature.” 
These remarks led me to collect together and write the 
following notes on such spiders as we know to occur, or to have 
occurred, with ants in Britain. I also take the opportunity to 
express some views I have formed on the origin of myrme- 
cophilous species. 
Now, between the true guests of ants, the indifferently tole- 
rated lodgers, the hostile persecuted lodgers, the true parasites, 
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