26 



BULLETIX 1453, U. S. DEPARTMENT OF AGRICULTURE 



is also employed in the course of undisturbed migration, the most 

 usual and reliable method of locomotion is by creeping. This always 

 brings the insect to a dark spot, if obstructions do not prevent, 

 whereas the leap is haphazard and is as likely to throw the insect 

 toward the light as toward the shadow. 



TYille (81) has made a study of the modes of larval progression. 

 He stated that locomotion by springing occurs in third-stage larvae 

 only, and is most pronounced within one day of pupation. 



A photograph of larvae of Piophila casei is reproduced in h of Fig- 

 ure 3. In Figure 5 is a comparison of the appearance of skippers 

 and the larvae of Lucilia sericata Meig., one of the common blowflies. 



INSINUATING ABILITY OF THE MAGGOTS 



An outstanding attribute of the larva is its remarkable insinuating 

 ability. Being pointed anteriorly, slender, and very strong, it is able 

 to enter exceedingly small crevices and therefore is difficult to con- 

 fine. Petri dishes and jars 

 closed with muslin secured 

 by tight rubber bands do not 

 confine the larvae. When 

 masses of larvae crowded to- 

 gether have moistened the 

 muslin covers of the jar 



i//» 



\f&.jp*- 





> %0 <C^N> 



9 » "M 



a 



liiilll 



containing 



them, i 



Fig. 5. — Larvae of PiopTiila casei (a), compared 

 with larvse of Lucilia sericata (&), one of the 

 common blowflies. Slightly enlarged 



able to force their way 

 through the close weave 

 of a good grade of cloth. 

 Six layers of cheesecloth 

 have failed to prevent the 

 escape of the maggots from 

 glass containers. The most 

 effective container is a paper 

 can, which absorbs the 

 moisture from the surface 

 of the larvae, making it 

 impossible for them to mount the sides. In glass vessels the efforts 

 of hundreds of larvae to escape soon coat the surface with a thin 

 oily film, which enables the maggots to cling to the glass. 



The penetrating power of the larva is useful to it in forcing its 

 way among the layers of connective tissue between the muscles, and 

 accounts for the depth at which maggots are found in recentty 

 infested meat. The ability of the newly hatched larva to enter a 

 small aperture may at times lead to infestation of wrapped meat in 

 cases where eggs are laid on greasy spots on the outside of the 

 wrapper. 



FACTORS RETARDING GROWTH OF LARVAE 



Xormally the two principal influences which inhibit larval devel- 

 opment are low temperature and starvation. The former is discussed 

 in some detail later in this bulletin under " Control measures," and 

 the influences of both are referred to in the consideration of the life 

 cycle (pp. 30-34). Starvation results ordinarily from the desiccation 



