Insects and their world 



easier problem, because the food material is not locked up in indigestible 

 cellulose. Saliva is used to soften the tissues, and partly digest them 

 before they are taken into the intestine. Many larvae that have a supply 

 of animal food provided for them — those of parasitic Hymenoptera or of 

 wasps — do this, and so do the larvae of blowflies, scratching at a piece of 

 meat with their mouth-hooks. 



Saliva is most efficiently used, however, by insects that pierce and 

 suck. Plant-bugs (Heteroptera and Homoptera), of which there 

 are a great many, push their proboscis into a leaf or a stem and inject 

 saliva, which dissolves the contents of the cells around, without the need 

 to break them open. A pool of liquid nutriment is formed, which is then 

 drawn back into the intestine. 



A similar method can be used to feed from other animals, and indeed 

 some bugs (e.g. Reduviidae) have made the transition. Where the prey 

 is another insect, the saliva can be used to paralyse or kill the prey, and 

 also to soften and Uquefy the tissues, so that the insect can be sucked 

 dry. Carnivorous larvae of water-beetles and water-bugs do this, and 

 so do the adults of robberflies (Asihdae) and danceflies (Empididae). 



When the prey is a warm-blooded animal the food material is blood, 

 rather than muscular and other tissue. The proboscis is stiff", and often 

 sharp too, and either enters a blood-vessel, or lacerates capillaries until 

 a pool of blood is formed beneath the skin. The funaion of the saliva 

 of blood-sucking insects is not so much to predigest the already Uquid 

 blood, as to stop it from forming a clot which would block the proboscis 

 or the intestine of the blood-sucking insect. 



We seem to have come gradually from the feeding of immature 



Fig. 27. A cicada, Order Hemiptera-Homoptera 



46 



