Lakes which appear frozen from the top never freeze completely. Only the top layer freezes and a thick layer of ice floats on water which remains liquid below and in which fishes and other aquatic animals survive. With the onset of winter water starts cooling. As it cools, it shrinks in volume and become denser, but only until it reaches 4°C. Below that temperature water expands and its density drops. This comparatively lighter water moves up and finally at 0°C turns into ice. Since the density of ice is less than that of water, the ice floats. Also, ice being a very poor conductor of heat, further cooling of the water below it stops. Thus the temperature of water below the ice layer remains at 4°C and fishes survive in it.
No animal can see in total darkness. However, some animals are capable of making use of faint light of the surrounding. Members of the cat family, like the tiger and cat or other nocturnal animals can see in near darkness because of the presence of large number of cells called rod cells in the retina. These cells are sensitive to dim light and help the animal to see in near darkness.
Spiders spin webs as a means of trapping insects. They have special organs called spinnerets located in their abdomen. Spinnerets are muscular organs which release the thread, independently of one another. Most spiders are equipped with three pairs of spinnerets. Each pair is fed by several silk glands which produce a sticky liquid that can be drawn into fine threads. The sticky liquid turns into a thread by solidifying on exposure to air. 
Besides chemicals called pheromones, bees use a kind of dance language to tell other bees in a hive where the food is. When a worker bee locates a source of food such as a tree in bloom, it returns to the hive and performs a ‘dance’. If it is a round dance, that is, if the bee just goes round and round, it only says that food is nearby. A more complicated waggle dance, in which the bee executes a kind of ‘figure of eight’ movement, gives information not only about the distance and direction of the source of food but also the quantity of food expected. It is now known that the bees use gravity and not the sun as the reference point while dancing. That the dance language really works has now been demonstrated beyond doubt by using robot bees.
Honeybees suck nectar from a wide variety of flowers. But each bee usually keeps to a particular kind of flower until its supply diminishes. The nectar is collected by the forager bee in an organ called the honey sac. Here the nectar is broken down to two sugars, fructose and dextrose, by the action of a special enzyme. On returning to the hive the bee empties the nectar load by disgorging it onto the mouth parts of the younger bees. They evaporate some of the water and concentrate the nectar. Glandular secretions further transform it. After this, the nectar is deposited in an empty storage cell in the honeycomb, where the nectar gradually thickens into honey by evaporation. To speed up evaporation bees in the hive fan their wings (26,400 times a minute) to set up additional air currents. After the cells are filled with honey these are sealed with wax by the bees.