OF WASHINGTON. 429 



hibit are indirectly traceable, in the heft of the body, the short 

 ness of the wings, and the general helplessness, especially of the 

 female, to the parasitic habit of the larva ; for the female here leads 

 a partially subterranean life, as it must be of advantage to the 

 larvae to be born in or near the burrows of the bee-victim. 



ECONOMIC BEARING OF PARASITISM. 



The effects of insect parasites upon the warm-blooded animals 

 they attack are very variable, depending in large measure upon 

 the character of the attack and the number of the parasites occur- 

 ing on any particular animal ; also on the previous condition of 

 the animal and its ability or inability to resist attack. Thus par 

 asites which are entirely external have the least effect, while those 

 which invade the internal parts cause most disturbance. Even 

 here, however^ the cases where they prove fatal are sufficiently 

 rare, while some authors deny that they ever do prove fatal. My 

 own experience would justify the conclusion that, while they 

 rarely are fatal in themselves directly, thev often produce death 

 indirectly by the emaciated condition of the host which follows a 

 bad attack, and which makes the creature subject to a whole 

 train of other troubles. The injury is often great in sensitive ani 

 mals, like the horse, while the money loss in the effects that 

 Hypoderma produces upon hides has been recognized as very 

 great. 



There can be no question that the presence in numbers of the 

 itch, scab and mange mites results in great derangement of the 

 activities of the skin, producing the unhealthful secretions char 

 acteristic of the particular species, and so interfering with the 

 normal activity as to produce serious results, and sometimes 

 death . 



External parasitic insects upon warm-blooded animals may 

 also, as in fact they are now known to do in some cases, act as 

 carriers of other forms of disease, and viewed from this stand 

 point their relation to the economy of animal life assumes a very 

 important aspect. Thus it is now generally admitted by the best 

 authorities that the common cattle tick is the sole agent in the 

 transmission from one animal to the other of the germs of Texas 

 or splenic fever. I remember how, some 25 years ago, while as- 



