Note on the Tachiiiidce ; by Francis Walker. 



Among the Diptera the proceedings of this tribe, each of 

 which passes the wliole of its existence, except the latter 

 end, in another living insect, are more interesting than the 

 hal)its of most other tribes, and a notice of their history, 

 which is comparatively simple and limited, may suitably 

 precede the history of the parasitic Hymenoptera, which is 

 very extensive, and complicated, and difficult to understand. 

 In the Northern Hemisphere their habitation maybe divided 

 into three principal regions, in each of which they have 

 p'assed to and fro ; America, Africa, and part of Europe, 

 and Asia including the rest of Europe, and this last region 

 should bo especially studied as it includes the British Isles. 

 A survey of the country may give some indications of the 

 track in tiieir iiittings and migrations, swift or slow, accord- 

 ing to the helps or hindrances which occurred to them. 

 These indications only refer to the last advance through 

 Asia to Europe; darkness hides all knowledge of their 

 earlier transition, and the darkness doubles eacli time in 

 the endeavour to retrace their preceding passages to and 

 fro, as the change of climate impelled them. After the last 

 glacial epoch twilight reveals part of their course and fancy 

 may represent the rest. They may be believed to have 

 ascended from the tropical regions in south-eastern Asia to 

 nortliern Asia and thence to Euro2)e and to have established 

 stations ; in these some kinds wholly stopped, others 

 stopped in part and proceeded in part, and others wholly 

 proceeded, and thus the geographical distribution was 

 effected. The Diptera in general by their facility of flitting, 

 and of quick increase, and of appropriating various states of 

 plants and animals are likely to l)e comparatively tlie first 

 insect population in a country which begins to a ftbrd means 

 for subsistence. lUit the flies here mentioned are in cir- 

 cumstances very diflerent from those of the Muscida' to 

 which they are nearly allied ; their progress and prosperity 

 depends on that of other insects, chiefly Lepidoptera, which 

 are their sustainers, or in whose early state their early state 



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