INSECT ECOLOGY 373 



are quite at home in the desert. The integument is possibly no thicker 

 than in other tenebrionids, but having a thick skin to begin with, these 

 forms have found a suitable environment and have thrived in arid 

 places. 



3. FOOD RELATIONS 



As regards its kind and quantity, food is, needless to say, a most 

 important condition of existence. Examples of food habits have been 

 given (page 212); here should be mentioned some of the more essential 

 facts*concerning food as an ecological factor. 



Classification of Food Habits. According to the nature of their 

 food, most insects may be classified as follows: pantophagous (omnivo- 

 rous); phytophagous (plant-eating, referring usually to the flowering 

 plants); monophagous (with a single food plant); oligophagous (with 

 several definitely fixed food plants) ; polyphagous (feeding indiscrimi- 

 nately on many plants); sarcophagous (carnivorous); harpactophagous 

 (predatory) ; entomophagous (parasitic on insects) ; saprophagous (feed- 

 ing on decaying substances) ; necrophagous (feeding on dead animals) ; 

 coprophagous (eating excrementitious material) ; mycetophagous (feeding 

 on fungi) ; micro phagous (on micro-organisms, as bacteria, yeasts, etc.) . 



Not all these categories will be considered here, but a few of them 

 need special mention. 



Microphaga. The pomace flies (Drosophila) famous as subjects of 

 investigation by geneticists, feed naturally in fermenting fruits, where 

 they find nourishment, not in the products of fermentation, but chiefly 

 in the yeasts that cause the fermentation. On sterilized glucose-agar 

 the larvae cannot grow unless yeast is added; and a medium of yeast 

 nucleo-protein, sugars and inorganic salts is a complete food for this 

 insect. (Loeb and Northrop, Baumberger.) 



Sarcophaga. Dipterous larvae that normally feed on decaying 

 animal tissue were raised from eggs to adults on a diet of banana and 

 yeast-agar, by Baumberger, who says that we must consider the 

 probability that all decaying or fermenting substrata are merely the 

 media on which fungous or bacterial food of insects is growing. 



Coprophaga. Larvae of the house fly were raised on bran mash 

 containing a heavy growth of molds. Sections through these larvae 

 showed a complete absence of all material except bacteria, fungous 

 spores, and yeast cells in the digestive tract. It appears probable that 

 the larvae feed on micro-organisms, and are associated with them in the 

 same manner as that of Drosophila and yeasts. (Baumberger.) 



