Foreign Objects — Secretions 313 



insect's back. The larvse of Midges (Chironomus) 

 make tubes for themselves of the sand or mud at the 

 bottom of the water wherein they live. The Caddis- 

 worms or larvae of the Trichoptera — another aquatic 

 group — are all case-makers, forming their dwellings 

 of small stones, leaves, twigs, fragments of rushes, or 

 the shells of water-snails (lyo)* 



Protective Secretions. — While the caterpillar of 

 Erastria scitiila shelters itself beneath a case made of 



Fig. 169. — Clothes' Moth {Tinea pellionclla, Linn.), with larva in and 

 out of its case. Magnified. From Marlatt (after Riley), Bull. 4 

 (n.s.), Div. Ent. U.S. Dept. Agr. 



foreign objects, the Scale-insects on which it preys 

 carry protective coverings made entirely of a substance 

 derived from their own bodies — a wax secreted by 

 the glands of the skin. This wax is produced in 

 fine threads which appear on the body of the newly 

 hatched coccid, ultimately interlacing to form a firm 

 shield or "scale" (fig. 170). The female insect 

 settles down to a sedentary life beneath her waxy 

 shelter, which at length completely covers her, 

 becoming attached around its edge to the leaf or 

 bark whereon she lives. Protective waxy coverings 

 of a like nature to those of the coccids are to be 



