HOUSE-FLIES 107 



tions. Any one who lies down on a sultry July or August 

 afternoon, and casts his eyes to the ceiling, is very likely 

 to see this manoeuvre repeated time after time. The 

 flies which I have captured dancing in this way have all 

 been males. When the little house-fly comes to rest on 

 a vertical surface, such as a hanging cord, its head is nearly 

 always turned downwards. 



5. The Staircase-fly (Homalomyia scalaris) is, like the 

 last, a little smaller than the common house-fly. It not 

 only abounds in houses, but also in streets and gardens. 

 This species is most certainly recognised by a large tubercle 

 on the inner side of the tibia of the middle leg. A number 

 of Homalomyia-flies may sometimes be seen out of doors, 

 dancing merrily in the sun, and an experienced eye will 

 sometimes detect two or even three different species in 

 the throng. The larvae of the Homalomyias are very 

 peculiar, and quite unlike those of any species of Musca. 

 Every segment bears a pair of plumed appendages, many 

 of them relatively large, which give a distinctive appear- 

 ance, not to be mistaken by any one who has ever 

 examined it. 



6. The Grey House-fly (Stomoxys calcitrans). This is the 

 fly that bites. It is very nearly of the same size as the 

 common house-fly, but its wings are more widely parted 

 in the resting attitude ; the body is more thickly clothed 

 with grey hairs ; and the eyes are not so red. When the 

 head is closely examined, a slightly curved proboscis is 

 seen to project forwards from it ; this encloses a sharp 

 lancet, which inflicts the wound. The larva is reared in 

 dungheaps, and hence this is a common fly in farm- 

 houses ; it is much less frequent in cities. 



7. The Yellow House-fly (Pollenia rudis). This is often 

 found on the windows of country-houses. It is larger 

 than the common house-fly, and its thorax is clothed with 

 soft yellow hairs. The fly often hibernates in the house, 

 and is generally seen in spring, long before the common 

 house-fly appears. 



