MISC. PUBLICATION 631, U. S. DEPT. OF AGRICULTURE 



spiracles, which in most species are located on short stalks. Each 

 posterior spiracle has one opening. In the second instar the posterior 

 end broadens in comparison with the anterior, the last segment be- 

 comes retracted into the twelfth, and the posterior spiracles, no longer 

 located on processes, possess 2 openings each. The third-stage larva 

 (fig. 44) is robust and much broader behind than at the head end; 

 the head segment is very short ; the last segment is as in the second 

 instar, with 3 slits to each spiracle. The length of the larva is about 

 1 mm. in the first instar, 1.5-7 mm. in the second, and 7-20 mm. in the 

 third. 



Etiology and Pathogenesis. — Three species — namely, G. nasalis 

 (Linnaeus), G. intestinalis (Degeer), and G. haemorrhoidalis (Lin- 

 naeus) — have been accused of causing subcutaneous myiasis in man. 



Figure 43. — First-stage larva : A, 

 Gastcrophilus nasalis; B, G. intes- 

 tinalis ; C, G. haemorrhoidalis. 

 (After Wells and Knipling (159, p. 

 201).) 



Figure 44. — Mature larva : A, Gas- 

 terophilus nasalis: B, G, intesti- 

 nalis; C, G. haemorrhoidalis. 

 (After Wells and Knipling, (159, 

 p. 203).) 



The first-stage larva bores through the epidermis; the exact location 

 of the tunnels in relation to the layers of skin is variable, but the horny 

 layer usually forms the roof of the tunnel and the epidermis or corium 

 its floor. The tunnels are often serpentine and may cross and re- 

 cross themselves ; they appear as raised red stripes, which advance at 

 one end and gradually fade out at the other. An intense itching 

 sensation is usually felt. 



The larva usually advances about 1 to 2 cm. daily, the progress 

 generally being more rapid at night. This infestation may end spon- 

 taneously or at times by suppuration. 



The disease is known by various names, such as creeping eruption, 

 creeping disease, larva migrans, myiasis linearis, rampant subcuta- 

 neous myiasis, hyponoderma, Hautmaulwurf (in Germany) , and volas- 

 satik (in Russia). All cases of creeping disease are not produced by 

 Gasterophilus, however; they may be due to Hypoderma or to nema- 

 todes, and in some types of cases the etiological agent is unknown. 



Stomach parasitism may occur in animals other than the horse ; such 



