94 THE CAUSES WHICH PROPAGATE 



rivalry alone or in company, in our apartments, porches, of 

 g'ardens ; and the autumnal brood of this species I have observed, 

 like the Winter Gnat, to pair of an October evening. All these 

 vertical curve dances seem similarly to be commenced by the 

 males, who as they flash out their colours or interferential glitter 

 in the air, attract their kind to the sport ; but the coupling I 

 have observed only to ensue towards the hush of evening. 



Insects that hover on the wing have wing-outlines resem- 

 bling that of a blade of the horticultural shears (Fig. 4), definable 

 as elongate and triangular, with a maximum breadth near the 

 base, and a costal edge rounded at the tip ; and Humming Birds 

 and other Sphinges have an expansile tail of hair they expand 

 when they poise. In the wing configuration, and resultant 

 specific motion, we seem to trace a transition from the preceding 

 group, for while the Orange-belted Hover Fhes poise, humming 

 singly, on open spots near swamps, woods, and bushes, now and 

 again attracting their kind to wheel in air, others, as the groups 

 of Yellow-ringed Gnats and their mute water-born allies, band in 

 gossamer clouds that lightly lift and slowly fall. As regards 

 these gregarious dancers, simmering evening flocks of blood- 

 thirsty gnats, midge, or mosquito, constituting the one Linnean 

 genus Ctilex, are only too familiar to the cottar on the borders of 

 extensive feus, rivers, and forests, and more than one alarm of a 

 rural cathedral being on fire has arisen from their smoky volumes 

 rising and rolling above the district steeple. The clouds of 

 plumy Chironomi, that spring from those scarlet worms so fre- 

 quently noticed in our kitchen water-barrels and tanks, are in 

 some places scarcely less dense ; and the pairing of one species, 

 among the reedy plash at Calais, I witnessed towards sun- 

 down one mild afternoon in the beginning of stormy No- 

 vember. The scene was extremely beautiful, the red 

 autumnal sun shining brightly on the silvery elfish masses 

 that lay along the old town moat like heavy marish damp, 

 and as each couple paired they struggled to gain the sere and 

 seedy plants bordering the bank, an attempt, however, in which 

 a majority failed, and dropping down were whirled away on 

 the sluice. The males and females of the ants emerge but to 

 commingle an hour of their hasty lives in these nuptial clouds, 

 both sexes twisting off spontaneously their pantomimic wings 



