OUTLINES OF ENTOMOLOGY. 19 



Many larvae, such as those of bees, flies and some species of beetle s, 

 have neither legs nor prolegs their movements, in consequence of 

 this lack, being much restricted. 



In their habits larvae are either active or inactive. The former 

 including by far the larger proportion of the young of insects are 

 capable of sufficient exertion to enable them to provide for their own 

 necessities. 



Inactive or sedentary larvae, on the contrary, are hatched in cells 

 or chambers, which they never leave, and subsist upon food previously 

 stored for their use, or, as in the case of bees and ants, they are the 

 objects of constant attention from the mature insects. 



In the course of their growth all larvae molt or shed their skins 

 several times. This singular process becomes necessary at intervals, 

 because the external covering will only admit of stretching to a limited 

 extent. A new skin is constantly forming under the outer one, and 

 when the latter becomes too tight it is after some preliminary fasting 

 and other preparation ruptured and cast off, and the larvae appears in 

 a new and for a time, more elastic dress. The usual number of molts 

 is four or five. A few insects of the lower orders molt but twice, while 

 others, especially certain aquatic species and others whose larval life 

 is long, molt from ten to twenty times. Sedentary larvae shed their 

 skins in shreds and by degrees. 



The length of larval life varies with the different species. Many 

 complete their growth in a very short time, often within a week, while 

 some continue to grow from one to several years. The average length 

 of larval life among herbivorous insects is about four weeks. 



When the limit of growth is reached the larva ceases to feed, and, 

 guided by instinct, prepares for its first transformation. Inactive larvae 

 spin a slight web around their delicate bodies, and some kinds are 

 sealed up in their cells by the mature iusects. 



Active larvae take various measures to secure themselves from ob- 

 servation and injury during the time when they shall be powerless to 

 escape from or defend themselves against their enemies. Some creep 

 into crevices of stones or bark, or hide ingeniously among crumpled 

 leaves. A large proportion burrow into the earth; others spin for 

 their protection thick, silken or parchment-like cocoons, while some 

 require nothing more than a retired nook in which to suspend them- 

 selves by slender but strong cables of silk. After a longer or shorter 

 rest in their various retreats, the larval skins are cast off for the last 

 time, and each insect appears in a new and entirely different form and 

 is termed a pupa. 



