How they perform the primary functions 



ture during the successive larval instars — that when the time comes to 

 metamorphose into an adult a complete reconstruction is needed. This 

 can be carried out only during a resting stage, when all normal activities 

 except respiration cease. 



This stage is called the pupa, from the Latin for a female infant or a 

 doll. It looks rather hke a modern sculpture, with the head, thorax and 

 abdomen, antennae, legs and wings, all present in the rough, but lacking 

 in detail, and held in a stiff, unnatural attitude (Fig. 15). Since this is a 

 vulnerable stage it is often protected by an outer casing. The mature 

 larva may build a case just before pupation, either by spinning silk into 

 a cocoon, or by shaping earth or wood fragments into a pupal cell. In the 

 more advanced groups of flies (Diptera), such as the blowflies and 

 allied families, the skin of the last larval instar is hardened into a seed- 

 like casing called a puparium. 



The pupa itself is always enveloped in its own cuticle or skin, whether 

 or not it is further enclosed in a cocoon or puparium. If the pupal skin 

 is arranged in such a way that the appendages are free to move, the pupa 

 is said to be exarate, or 'free'; if the appendages are swaddled down to 

 the body the pupa is obtect. 



Pupae of both types normally remain still, or at any rate, inactive. 

 Many insects have a period of activity just before they emerge as adults, 

 but this is now considered to be a distinct stage of metamorphosis, 

 during which the insect is adult, but is still confined within the pupal 

 skin. It is then called a pharate adult. It is the pharate adult that often 

 climbs out of the water or soil, so that the adult can emerge in the open 

 air. 



57 



