Insects and their world 



sting sometimes has barbs, similar to the saw-teeth of the sawflies, and 

 in the honey-bee and some others these barbs are so big that the sting 

 is left behind if it enters the human skin. 



The eggs of insects may be of almost any shape, from a sausage to a 

 sphere, or a disc (Fig. 29). Some rounded ones are flattened on one side, 

 where they stick to a surface. There is no certain way of distinguishing 

 them from the eggs of other invertebrate animals, but since there are 

 more different kinds of insects than there are of all other animals to- 

 gether, you will most often be safe in assuming that any small eggs that 

 you find are probably those of an insect. 



Some insects produce only one egg at a time; others, like the queens 

 of the bees and termites, become mere egg-laying machines, and 

 produce hundreds, or thousands of eggs over a period of time. 



Many insects merely drop their eggs, either scattering them at 

 random, or dropping them into a mass of material that is suitable for 

 the larvae to feed on: e.g. dung, rotting vegetable or animal materials, 

 or fruit. Those whose larvae live among vegetation may often attach 

 their eggs to leaves or stems (Fig. 68), often to the underside of a leaf, 

 where they will not be easily seen by enemies. If the larvae are going to 

 live in water, the eggs are often to be found attached to plants standing 

 in, or overhanging ponds and streams. The eggs of the lacewing, 

 Chrysopa, are each attached to a plant by a fine thread, which hardens 

 quickly into a thin stalk. 



There are various ways in which the eggs can be protected. Many 

 Orthoptera enclose a batch of eggs in a pod (or ootheca), which may 

 be buried in the groimd. Some Homoptera, especially Fulgoroidea 

 ('lantern-flies'), cover their eggs with wax filaments. We have already 

 mentioned woodboring insects, which insert their eggs into the wood, 

 and their parasites, which follow them there. 



The embryology of insects, that is their development from a single 

 cell into a larvae that can live independently, is outside the scope of the 

 present work. It is treated in detail in the textbooks of entomology. 



When the larva is ready to hatch it breaks through the egg-shell 

 mainly by pushing hard. The shell has certain lines of weakness along 

 which it is easily split, and many larvae have so-called 'egg-bursters' 

 to help them to do this. These are projections, usually on the head 

 which seem to exist only for this moment. They do not so much sht 

 the egg-shell, as prick it Hke a balloon, whereupon it flies apart. 



Normally only one larva hatches from each egg, but in a few insects 

 the single fertilised ovum may give rise to two or more embryos: 

 perhaps to a great number. Polyembryony, as it is called, is highly 

 developed in parasitic Hymenoptera, where as many as a thousand 



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