Collecting and Rearing Insects 667 



Tradescantia (wandering- jew or inch-plant) is also useful. Avoid the 

 use of algae (pond-scum). The function of the plants is chiefly to oxygenate 

 the water. The roots of cress will furnish food for some vegetable-feeding 

 animals. 



An aquarium, to be in good condition, must be kept aerated, must be 

 kept clean, and its temperature must not be suddenly changed. Sufficient 

 air is sometimes maintained by plant-life alone. Unless this proves to be so, 

 shown by the healthy condition of both plants and animals, dip up a few 

 cups of water every day and let it fall back into the aquarium. All uneaten 

 food, dead animals, or decaying leaves must be removed at once. An 

 apparatus for removing such is described in a later paragraph. 



The aquarium should be in the light to enable the plants to produce 

 oxygen, but not in direct sunlight. If it stands in a sunny window, it should 

 be screened from the sun. Water lost by evaporation must be replaced, 

 but the fresh water must not differ materially in temperature from that in 

 the aquarium. If a film appears on the surface of the water, it is due to 

 bacteria and dust. It prevents absorption of air at the surface of the water. 

 It may be removed by absorbent paper (newspaper or blotting-paper). It 

 may be prevented by thorough cleanliness and by using a coarse cheese- 

 cloth cover when not under observation. Never give more food than is 

 eaten. 



Implements for use in connection with the aquarium are the following: 

 A small dip-net made by twisting a wire about a bottle for the ring and the 

 ends about each other for a handle, the net to be made of coarse cheese- 

 cloth or bobinet, used for removing certain objects; a piece of flannel wrapped 

 about a stick for cleaning the sides of algae, which are bound to accumulate. 

 For removing small particles from the bottom, a ^-inch glass tube long 

 enough to reach to the bottom is useful. Close the upper end with the finger, 

 hold the other end over the object to be removed, lift the finger, and the 

 water will rush up the tube, carrying out the object. Replace the finger on 

 the upper end and lift the tube out of the water. For removing a quantity 

 of sediment, a long narrow chimney tightly fitted at each end with a cork 

 is required. Insert through the center of the corks a short piece of glass 

 tubing, and use as described for the simple glass tube. 



To stock the aquarium choose animals that are adapted to life in still 

 water, and keep cannibals by themselves. A wire netting will keep in flying 

 insects. 



Of the insects that may be kept in an aquarium some spend their entire 

 life in the water, while others are aquatic during one stage of existence only. 

 Among the insects easily kept in aquaria are the predaceous diving-beetles, 

 the young of which are known as water-tigers and feed on small earthworms 

 and other insects, as mosquito-wrigglers, May-fly nymphs, etc.; the water- 



