THE DOCK FALSE-WORM. 



13 



The larvae molt five times, passing through, six stages or instars. 

 During the first and second instars, or until the second molt, the 

 larvae usually remain on the same leaf. After this they become 

 more or less restless and find their way to other leaves, especially 

 if the first leaf has been supporting several larvae and is mostly 

 eaten. The younger larvae lie securely in the hollows they have 

 eaten out of the leaf, clinging to the lower side of the upper epider- 

 mis, and they are not easily dislodged. The large larvae simply lie 

 at full length on the under surface, and if disturbed, curl up the 

 posterior part of the body, holding to the leaf only by the thoracic 

 legs. If the disturbance continues they loosen their hold and drop 

 to the ground, later finding their way back to the leaves. This 

 death feigning, if it may be so called, is a characteristic of this type 



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Fig. 4.— The dock false-worm: Diagram showing seasonal abundance oi the generations. (Original.) 



of sawfly larva, and where the larvae are numerous a veritable shower 

 of them will be produced by shaking the plants. 



The larva ordinarily molts on the leaf where it has been feeding, 

 but sometimes it will migrate to the leaf stem or the base of the 

 plant. It remains quiet for a time before molting, and then the 

 usual peristaltic motion is noticeable. The integument of the head 

 soon splits along the dorsal line to the clypeus, the split forking 

 here and following the clypeal sutures. This frees the head of the 

 larva, which is pushed out, followed by the thorax, and a little time 

 elapses before the mouth parts and thoracic legs are pulled out of 

 their old coverings. Since the posterior part of the old skin is at- 

 tached to the leaf by means of the hooks on the abdominal legs, the 

 larva is soon able to crawl out, the whole operation occupying six 

 or eight minutes. After molting the larva rests for 10 or 15 minutes 

 in order to allow the new integument to harden somewhat, where- 

 upon it is ready to feed again. The molted integument is not eaten, 

 but remains adhering to the leaf or stem. 



