i go ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



to plants. Where, as largely in Water- Bugs, small creatures are 

 selected as victims, these are killed as a result of the feeding 

 operations, and the true carnivorous habit is illustrated. But 

 Bugs which feed on the blood of relatively large animals may 

 be described as external parasites. The most notable example 

 is the wingless Bed Bug (Cimex lectularius), which is fortunately 

 a favourite prey of several other insects, including some belonging 

 to the same order (e.g. species of Reduvius). The True Lice, 

 which live entirely upon the blood of Mammals, are very possibly 

 to be regarded as minute Bugs, which have lost their wings and 

 become modified in other ways as a result of 

 the parasitic habit. Considering the mode of 

 life, their small size is clearly an advantage, 

 and their remote ancestors were probably 

 larger insects. 



FLIES (DIPTERA) AS PARASITES. A num- 

 ber of these insects are endowed with mouth- 

 parts adapted for piercing and sucking, and 

 are notable blood-suckers, the habit being com- 

 monly restricted to the females. Gnats and 

 Mosquitoes, Midges, Sand - Midges, Breeze- 

 Flies, and Tsetse- Flies, may be cited in illus- 

 tration - A very interesting series of modifica- 

 is] beiow. The short lines to tions is found within the limits of one family 



left show actual length. / r r r 7 \ 1-1-11 



\Hippoooscidfe), which illustrates the reduction 

 of wings resulting from the parasitic mode of life. The feet are 

 provided with strong claws for holding firmly to the animals 

 attacked, and males as well as females are blood-suckers. One 

 of the least modified species is the Forest- Fly (Hippobosca equina), 

 which infests horses. Well-developed wings are present, but not 

 much used, as these insects fly unwillingly. Another somewhat 

 similar form (Lipoptena cervi) lives on the Red- Deer, and its wings 

 are either shed or bitten off as soon as a host has been secured. 

 The wings of the Swallow- Fly (Stenopieryx hirundinis] are small 

 and narrow, while in the so-called Sheep-" Tick" (Melophagus 

 ovis) they are altogether absent (fig. 1135). So also in the 

 Bee-" Louse" (Braula cczca], a minute insect that infests bees, 

 and some curious little parasites (species of Nycteribia] that have 

 been found among the fur of bats. 



Some of the insects of this order live within the bodies of 



