24 BULLETIN 1453, U. S. DEPARTMENT OF AGRICULTURE 



number of the early writers, principally on account of the remark- 

 able saltatorial ability displayed by the maggot. The jump of the 

 full-grown larva has given the species its common name. The writer 

 concludes that there are three larval instars; these have been iden- 

 tified by Sakharov (67) and by Wille (81). 



FIRST-STAGE LARVA 



The first-stage larva appears as a diminutive mass of translucent 

 jelly. When it leaves the collapsed, flat eggshell behind, its progress 

 is marked by a groove in the grease on the meat. Shortly after the 

 hatching begins all the larva? are free and soon seek the crevices of 

 the meat, where they feed en masse. The clustering habit of these 

 maggots is marked throughout the larval life. Larva? transferred 

 from one piece of meat and scattered about on another may be found 

 the next day gathered in one or two groups. The effect of group 

 feeding is advantageous to the individual because of the decided 

 softening effect produced on the food. All stages of the larva? 

 exhibit strong negative phototropism. 



As with muscoid larvae in general, the principal taxonomic characters of the 

 present species are the deeply pigmented oral hooks and cephalopharyngeal 

 framework and the spiracles. A minute set of oral hooks and a very small 

 supporting skeleton are visible in the first-stage larva, but no anterior spiracles 

 are present ; the tracheae in the anterior region end in fine branches within the 

 tissues. Otherwise the tracheal system is very similar to that of subsequent 

 instars. The posterior spiracles are conspicuous. 



Observation of first-stage larva? in a shallow drop of water on dark cardboard 

 can be made under the binocular. The principal concern of the insect under 

 these conditions is to keep the spiracles above water, and to this end the caudal 

 extremity of the body is kept elevated, and whenever possible the spiracles 

 penetrate the surface film. The excrescences on which the spiracles are situated 

 are movable at the will of the larva, which feels about with them in attempts 

 to locate a supply of air. The writer has observed first-stage larvae to hold the 

 two spiracular openings in close contact with one another, evidently for the 

 purpose of effecting a more complete closure of the respiratory system. 



SECOND-STAGE LARVA 



The larva of the second stage is provided with a rather slender, black 

 cephalopharyngeal framework and slender mouth hooks. The anterior spiracles 

 are present and consist of a pair of flat, yellow, fan-shaped processes arising 

 between the second and third segments. Their distal edges are digitate. When 

 closed these spiracles are withdrawn beneath the anterior margin of the third 

 segment. The posterior pair of spiracles is very evidently the pair most used ; 

 larvae in moist meat arrange themselves so that these breathing apertures are 

 exposed, whereas the anterior spiracles are not usually in free contact with 

 the air. 



LARVAL SKINS 



The cast skins of the first and second stage larva? may be separated 

 from a meat culture by vigorously dousing the infested meat in water, 

 allowing the suspended matter to settle, pouring off most of the clear 

 liquid, and adding fresh water. This process results in concentrating 

 larva? and cast skins in a small dish of clear water. In collections 

 made in this way only two sizes of skins are found. 



Skins of the first-stage larva are 1.5 to 1.8 millimeters in length, with a 

 dorsal split at the anterior end and typically with several of the posterior 

 segments invaginated. This infolding apparently results from the pull oc- 

 casioned by the friction between the forward-moving body of the molting insect 



