LICE WHICH AFFECT DOMESTIC ANIMALS 341 



nine months apart from the host. This seems exceptional as we have 

 never observed longevity to exceed three weeks. While specimens of lice 

 may drop off with feathers, we find in the method of treatment which is 

 described below that no concern need be felt for the reinfestation of a 

 flock from this source. It also appears that wild birds play very little 

 part in the carrying of these pests. Of course it is possible that sparrows 

 or other birds intimately associated with domestic fowls might accident- 

 ally carry a few specimens from one yard to another. 



Injury and Losses. — It is difficult to weigh the loss produced by lice. 

 It is generally believed by poultrymen that where they are at all abundant 

 they materially affect the development and Qgg^ production in fowls. Cer- 

 tain it is that young chicks are frequently killed by the attack of the head 

 louse and this also applies to young turkeys and ducks. Just how the 

 injury is produced is still a matter of debate. Since the lice do not suck 

 blood it is generally believed that the injurious effects are produced by 

 the irritation caused by the gnawing and running about of the parasites. 

 We have seen repeated instances of the rapid increase in weight of grown 

 fowls after they have been freed of lice and experiments now under way 

 seem to indicate clearly that egg production is markedly affected by even 

 moderate infestations of lice. In addition to these adverse effects it has 

 also been found that lice, especially when present in numbers, mutilate 

 the plumage of the fowls. This is of special importance in show 

 birds. 



While no disease has been demonstrated to be carried by poultry 

 lice, it is not improbable that they may play a part in the transmission 

 of some maladies of fowls. They have been suspected of being concerned 

 in the spread of the so-called chicken pox, or sore head, and favus. 



Methods of Control. — While there are a number of insecticides which 

 are fairly satisfactory in reducing the number of lice on poultry, experi- 

 ments carried out by Mr. H. P. Wood and the writer at Dallas, Texas, 

 indicate that none of them are as satisfactory as sodium fluoride. The 

 commercial grade ranging from 90 to 97 per cent NaF is used. This is 

 a white powder readily soluble in water and with comparatively low toxic 

 effect on the higher animals. It has been found that one light applica- 

 tion is sufficient to completely rid a fowl of all species of lice. The action 

 of the material is rather slow, especially when it is used in the dust 

 form. Usually it takes about four days for all lice to disappear 

 from the feathers. Since the lice chew their food and since other para- 

 sites which suck the blood from the host are not destroyed to a large 

 extent, it is believed that the material acts largely as a stomach poison. 

 Hatching of the eggs does not appear to be prevented but the young lice 

 succumb very soon after emerging from their shells. 



Sodium fluoride may be applied either as a powder or in solution. 



