176 INSECTS AND MAN 



by some epidemic and lie along the banks of the streams 

 in a dead or dying state. Whenever the Paraguayans find 

 the dead capybaras, they know that an outbreak of mal de 

 caderas is imminent. " There is a striking analogy between 

 this mortality among the capybaras, which precedes out- 

 breaks of caderas, and that among rats, which precedes 

 epidemics of plague." In 1910 there was a great mortality 

 among the capybaras of Paraguay, in which paralysis of 

 the hind quarters was a well-marked symptom, and the 

 caderas trypanosomes were found in their blood for the 

 first time ; as a rule, however, these rodents seem to suffer 

 little inconvenience from the trypanosomes, but, needless 

 to say, the fact that the parasites exist in their blood 

 renders their proximity to horses, asses, and mules 

 dangerous. 



EOT FLIES 



The bot flies, or (Estridce, are of great importance, on 

 account of their parasitic habits, their attacks being con- 

 fined to vertebrates and, so far as is known, to mammals. 

 The larvae are fleshy, headless maggots, composed of twelve 

 rings or segments, which are often spiny, to assist in 

 locomotion. Between the first and second segments two 

 anterior, external breathing organs may always be dis- 

 tinguished, as may two posterior ones, protected by horny 

 plates, on the last segment. They all live parasitically 

 in various parts of the bodies of mammals, such as the 

 alimentary canal, the nasal passages and throat or the 

 subcutaneous tissues. The adults are all heavy-bodied, 

 generally hairy, and are characterised by their small eyes 

 and antennae, the latter being sunken into pits on the 

 front of the head. Naturally, the habits differ in different 

 species, but, in every case, the eggs are deposited on the 

 animal host, although, in the sheep bot fly, living larvae 

 may take the place of eggs. All the adults frequent warm 

 sunny spots, and most of them pass through this stage 



