119 



ON THREE NEW SPECIES OF GAMASID MITES FOUND 



ON RATS. 



By Stanley Hirst. 

 (Published by permission of the Trustees of the British Museum.) 



The great majority of the GaMxVSIDAE are not parasitic in habit, but a number 

 of true parasites belonging to this family are known to occur on vertebrates and 

 on arthropods. They are most often found on birds and small mammals, 

 especially on bats and rodents. 



Gamasid mites belonging to several different genera are known to occur on the 

 species of rats which frequent human habitations ; the following is a list of these 

 genera: — Myonyssus, Leiognathus ( = Liponyssus), Dermanyssus (Lipouyssoules), 

 Laelaps and Haemogamasus. In vie^v of the possibility that some of the mites 

 of this family found on rats may convey plague or leprosy to human beings, 

 special attention ought to be directed in future to their habits and distribution. 

 Numerous cases of Dermanyssus avium attacking human beings have been 

 recorded by various authors and more than one species of Laelaps and of Leiog- 

 nathus have been found on man,* although, of course, not their proper host. 



In the genus Laelaps the fingers of the chelicerae (mandibles) of the female are 

 rather short, fairly stout, and armed with distinct teeth (instead of being slender 

 and pointed, as is usually the case in Leiognathus, or united to form a very long 

 style, as in Dermanyssus) ; one would imagine, indeed, from the general appear- 

 ance of the chelicerae, that the mites of this genus were not parasites, but preyed 

 upon other arthropods. Dr. C. Tiraboschit and the late Mr. W. W. Miller! 

 state in their papers, however, that species of Laelaps occurring on rats are true 

 parasites, and suck the blood of their hosts. In other details of structure, 

 especially in the presence of a series of minute denticles on the ventral surface 

 of the capitulum, most of these parasitic species of Laelaps present so much 

 resemblance to Leiognathus, etc., that I think they should be placed in the 

 same subfamily (Dermanyssinae), instead of in the separate subfamily 

 (Laelaptinae), in which they are usually put. 



The figures of Dermanyssus muris have been drawn by Mr. Horace Knight, 

 those of L,aelaps echidninus by Mr. Engel Terzi. 



* P. Megnin's "Parasites et Maladies Parasitaires " (1880) and Prof. L. G. Neumann's 

 " Treatise on the Parasites and Parasitic Diseases of Domesticated Animals " (English Edition, 

 1892). Neumann has also published an account of a case in which Laelaps stabularls, Koch, was 

 found in great numbers in a house and seriously affected the health of one of the inmates 

 (C. R. Soc. Biol. (9) v, 1893, p. 161). See also my little paper " On two new Parasitic Acari of 

 the genus Leiognathus, Cn." (Bull. Ent. Res. iii, 1912, p. 369). A number of instances of the 

 Gamasid parasites of rats and birds making attacks on human beings in Australia are given by 

 Dr. J. Burton Cleland in an interesting paper entitled " Injuries and Diseases of Man in 

 Australia attributable to animals (except insects) " (J. Trop. Med. xvi, no. 3, 1913, p. 43). 



-j- Arch. Parasit., Paris, viii, 1904, p. 342. 



% Washington, D. C, Treas' Dept.. Pub. Hlth. Mar. Hosp. Serv., Hyg. Lab., Bull. no. 46, 

 1908, p. 25. 



