Julv, 1907.] THE VICTORIAN NATURALIST. 61 



THE NEGATIVE PHOTOTAXIS OF BLOW-FLY 

 LARV^. 



By Prof. A. J. Ewart, Ph.D., D.Sc, F.L.S., &c. 



{Read before the Field N'atiiralists' Club of Victoria, I3th May, 1907.) 



On moving a heap of manure recently many thousands of active 

 maggots were left behind, and it vvas noticed that these 

 immediately began to crawl rapidly towards some loose earth 

 lying at the foot of a tree, in which they buried themselves, 

 traversing a distance of 5 to 12 feet before doing so. The 

 phenomenon was a remarkable one, since hundreds of the larvae 

 could be seen crawling rapidly in an almost straight course for 

 the base of the tree, without a single one progressing in the 

 opposite direction or diverging to any extent laterally. That the 

 movement was not directed by ordinary vision or by smell is 

 shown by the fact that a piece of manure placed within an inch 

 of the maggots on the outward side did not attract them, and 

 that they passed such heaps unnoticed unless they were actually 

 in their path. In the latter case the larvae at once buried them- 

 selves in the heap. The path of movement towards the tree was 

 slightly down hill, but on changing the position of the grubs they 

 crawled up Iiill towards the same destination, and also crossed a 

 ridge of hard soil placed across their downward path. Evidently, 

 therefore, the response is not a geotropic one. 



The only remaining directive agency is light. In crawling 

 towards the tree they steadily progressed towards light of less and 

 less intensity, and the finding of loose soil at the base of the tree 

 was purely an accident, for if any of the soil was loosened in 

 their path they buried themselves in it, and also crawled into and 

 remained in little inverted boxes of black paper placed before 

 them. On repeating the observations with fresh material at 

 night time the repellant action of a strong beam of light was very 

 obvious, any portion of ground on which the light vvas turned 

 being soon cleared of grubs, and by manipulating the light the 

 grubs could be driven in a particular direction like a flock of 

 sheep. In feeble light the grubs often do not know which way to 

 turn, and may move irregularly, but even then the majority can 

 be seen to avoid the light either by crawling away laterally or by 

 burying themselves in any loose material at hand. They will do 

 the latter even in darkness, and undoubtedly possess a strong 

 sense of contact. It is evident from the observations recorded 

 that they also possess a strong negative phototactic irritability, 

 such as is shown in equal degree by many of the freely motile 

 lower plants. 



The latent period of response is from i to 3 seconds, and 

 since the larvae move with a speed of about a foot a minute, a 

 narrow beam of strong light may be crossed by them with 



