35 



BOTS — LARV.^. OF THE GAD-FIA'. 



There are such erronooiis opinious extant concerning the Ijot and 

 the depredations it is supposed to commit upon the horse that a some- 

 what careful study should be made of it. 



Of the many insect parasites and tormentors of solipeds the gad- 

 flies (G^stridae) are of the most importance. Cobbold, who is the best 

 autlioritj^ on the subject, says: 



The common gad-fly (Gastrojih Has equi) attacks the anim^al while grazing late 

 in the summer, its object being, not to derive sustenance, but to deposit its eggs. 

 This is accomplished by means of a glutinous excretion, causing the ova (eggs) 

 to adhere to the hairs. Tlie parts selected are chiefly those of the shoulder, base 

 of the neck, and inner part of the fore legs, especially about the knees, for in these 

 situations the horse will have no difficulty in reaching the ova with its tongue. 

 When the animal licks those parts of the coat where the eggs have been placed 

 the moisture of the tongue, aided by warmth, hatches the ova, and in something 

 less than three weeks from the time of the deposition of the eggs the larvae have 

 made their escape. As maggots they are next transferred to the mouth and 

 ultiuiatel}- to the stomach along with food and drink. A great many larvae i^erish 

 during this passive mode of immigration, some being dropped from the mouth 

 and others being crushed in the fodder during mastication. It has been calcu- 

 lated that out of the many hundreds of eggs deposited on a single horse scarcely 

 one out of fifty of the larvse arrives within the stomach. Notwithstanding 

 this waste the interior of the stomach may become completely covered (cuticular 

 portion) with bots. Whether there be few or many they are anchored in this 

 situation chiefly by means of two large cephalic hooks. After the bots have 

 attained perfect growth they vohmtarily loosen their hold and allow themselves 

 to be carried along the alimentary canal until they escape with the feces. In all 

 cases they sooner or later fall to the ground and when transferred to the soil they 

 bury themselves beneath the surface in order to undergo transformation into the 

 pupa condition. Having remained in the earth for a period of six or seven weeks 

 they finally emerge from their pupal-cocoons as perfect dipterous (winged) insects — 

 the gad-fly. It thus appears that bots ordinarily pass about eight months of their 

 lifetime in the digestive organs of the horse. 



The si^ecies just described infest chiefl}' the stomach and duode- 

 num — small gut leading from the stomach. 



Another species of oestrus affecting the horse is the O'strus hcemor- 

 rhoidalis. These are found fastened to the mucous membrane of the 

 rectum (last gut), or even outside upon the anus, and occasion mucli 

 irritation and annoyance, and, at times, require to be removed by the 

 fingers or forcejjs. 



The opinion, almost universally entertained, that bots frequentlj" 

 cause colicky- i)ains, is erroneous. It is very common to liear bystand- 

 ers declare that almost every horse with abdominal pains "has the 

 bots," and their suggested treatment is always varied and heroic. 



Almost all horses in the country, as well as horses in the cities dur- 

 ing their first jear there, have " the bots." It is in exceptionally rare 

 instances that they produce any appreciable symptoms or disturb- 

 ances. In my own practice I have never known bots to be tlie cause 



