THE DISPERSAL OF SPIDERS 

179

Linn., 

Theridiosoma gemmosum 

L.K.,

 Theridion pulchellum 

Walck., 

Dipoena melanogaster 

C.L.K.,

  D

.

 prona 

Menge., 

D

.

 tristis 

Hahn., 

Enoplognatha schaufussi 

L.K.,

 Anacotyle stativa 

Sim., 

Lophocarenum 

stramineum 

Menge, 

Hybocoptus decollatus 

Sim., 

Colobocyba mitis 

Camb., 

Trichoncus saxicolus 

Camb., 

T

.

 affinis 

Kulcz., 

Acartauchenius 

scurrilis 

Camb., 

Porrhomma oblitum 

Camb., 

Centromerus subacutus 

Camb. 

We need have little doubt that temperature is the main factor 

restricting these species to this small area of England. 

Now the sea is not the only element which creates isolation. We 

have species which are restricted to particular habitats, such as 

mountain tops, caves, sandhills, marshes and ants

'

 nests. It has been 

suggested that the mountain species retreated to high altitudes from 

the plains they inhabited when the Ice Age was waning, but there has 

never been an age of caves, of sandhills, of marsh or of ants! The 

inhabitants of these  islands  have had to colonize them across 

inhospitable areas in which they could not survive, and it cannot be 

suggested that man assisted them in this feat. Faced with this difficulty 

Berland is now prepared to concede that spiders can disperse 

themselves short distances by air, so our views are drawing nearer. I 

go further, and explain, for instance, the distribution of such species as 

Coryphaeolanus holmgreni

,

 Erigone tirolensis

,

 Hilaira frigida 

and 

Meioneta nigripes 

on many suitable mountain tops and on isolated 

Arctic islands, such as Jan Mayen, Bear Island and Spitzbergen, as 

being due to their powers of dispersal by air. These islands can have 

had no spider fauna during the last Ice Age, and when the ice retreated 

there was no land bridge connecting them to a mainland. As for their 

colonization of mountain tops, let us not forget the frequent discovery 

of numerous invertebrates on their snowy slopes, invertebrates which 

have been carried downward (as if there were some magnetic force 

directing them thither) in the downward air currents which airmen so 

frequently experience over mountains.