464 DIPTERA CHAP. 



But tlie most remarkable of all the Mycetophilid larvae are 

 those of certain species of Sciara, that migrate in columns, called 

 by the Germans, Heerwurm. The larva of Sciara militaris 

 lives under layers of decomposing leaves in forests, and under 

 certain circumstances, migrates, sometimes perhaps in search of a 

 fresh supply of food, though in some cases it is said this cannot be 

 the reason. Millions of the larvae accumulate and form them- 

 selves by the aid of their viscous mucus into great strings or 

 ribbons, and then glide along like serpents : these aggregates are 

 said to be sometimes forty to a hundred feet long, five or six inches 

 wide, and an inch in depth. It is said that if the two ends of 

 one of these processions be brought into contact, they become 

 joined, and the monstrous ring may writhe for many hours before 

 it can again disenffage itself and assume a columnar form. 

 These processional maggots are met with in Northern Europe 

 and the United States, and there is now an extensive literature 

 about them."'^ Though they sometimes consist of almost incredible 

 numbers of individuals, yet it appears that in the Carpathian 

 mountains the assemblages are usually much smaller, being from 

 four to twenty inches long. A species of Sciara is the " Yellow- 

 fever fly" of the Southern United States. It appears that it 

 has several times appeared in unusual numbers and in unwonted 

 localities at the same time as the dreaded disease, with which it 

 is popularly supposed to have some connection. 



Fam. 3. Blepharoceridae.^ — Wings 'with no discal cell, hit 

 with a seconcliinj set of crease-like lines. The flies composing 

 this small family are very little known, and appear to be 

 obscure Insects with somewhat the appearance of Empidae, 

 though with strongly iridescent wings ; they execute aerial 

 dances, after the manner of midges, and are found in Europe 

 (the Pyrenees, Alps and Harz mountains) as well as in North 

 and South America. Their larvae are amongst the most re- 

 markable of Insect forms ; indeed, no entomologist recognises 

 them as belonging to a Hexapod Insect when he makes a first 



1 See Guerin-Meneville, Ann. Soc. cnt. France (2) iy. 1846 ; Bull. p. 8 ; and 

 Kowicki, Vcrh. Ges. Wien, xvii. 1867, SB. p. 23. 



2 For details as to the family of. Osten Saoken, Berlin, cnt. Zeitschr. xl. 

 189.5, p. 148 ; and for the larvae F. Miiller, Arch. Mus. Rio-Jan. iv. 1881, 

 p. 47. The name " Liponeuridae " was formerly applied by some authorities 

 to this family, but it is now generally recognised tliat Blepharoceridae is more 

 lesitimate. 



