FLEAS 109 



State of affairs and it remains to be seen what are the limiting factors 

 within the nest for each species. 



The total records of these house-martin fleas, collected from all 

 known sources, in Great Britain and Ireland are as follows : — 



C. hirundinis Cfarreni C, rusticus . rothschildi 



61 records 43 records 33 records i record 



It seems likely that C. rusticus is on the increase in this country. Up to 

 1923 it had only been recorded six times and was absent from both 

 Tring and Ashton. In 1935, Rothschild examined sixteen nests from 

 these two localities and it was present in them all. The three species 

 were represented as follows : — 



C. hirundinis Cfarreni C. rusticus 



722 74 353 



(present in 15 out (present in 11 out (present in 16 out 



of 16 nests) of 16 nests) of 16 nests) 



It is a well known fact that in recent years a few British butterflies, such 

 as the comma and white admiral, have increased their range and 

 changed their status from "rare" to "common." Similar fluctuations 

 may easily occur among the Aphaniptera. 



The vast numbers of these fleas in single nests raise the question 

 as to what factors limit the size of a population. At present it is a 

 complete mystery why a house-martin's nest should regularly harbour 

 hundreds, if not thousands, of fleas and other birds' nests, apparently 

 equally suitable, a mere dozen or so. 



The distribution of these fleas outside Britain and their origins are 

 dealt with on pages 85 and 94. 



The sternites of the males and receptaculum seminis of the females 

 are figured on Plates XIII-XVI. The vermiform shape of the body 

 of the receptaculum of C. hirundinis, C. farreni and C. rusticus should be 

 compared with the barrel-shaped organ of 0. rothschildi. The contrast 

 is striking (see pp. 92-95). 



It is worth noting that the first specimen of C. rusticus described in 

 this country was a straggler off a wood-pigeon. It is one of our smallest 

 bird fleas, generally measuring less than 2 mm. in length. 



