205 



Family Empidse — The Dance Flies 



Flies of small to medium size, though rarely over 10 mm. in length. 



Head more or less spherical, loosely connected with the thorax; 

 males holoptic or diehoptic, the face sometimes almost obliterated by 

 the approximate eyes; ocelli present. Antenna porrect, composed of 

 two or three segments, with or without an apical style or arista, or 

 with dorsal arista; face receding or slightly prominent below, never 

 with a strong mystax. Proboscis short or long, usually rigid. Thorax 

 sometimes long and narrow, usually sliort, often strongly convex above. 

 ]\Iale genitalia generally of complicated structure, often large or very 

 large; ovipositor sometimes long and chitinized. Wing venation 

 simple, the wings rarely absent or reduced in size; squamffi small; anal 

 and second basal cell sometimes absent or incomplete. Legs usually 

 slender, sometimes with structural peculiarities sucli as elongated coxai 

 or femora, the femora or tibiii; often thickened and with spines or 

 tubercles or with processes or fringes of scales; pulvilli distinct; 

 empodia usually membninous and liiu'ai'. 



The adults are found almost everywhere but the Empids are rare 

 in arid regions. They are most abundant in moist places, especially 

 in woods, along streams and on the shores of ponds and lakes. All 

 are predaceous, feeding upon smaller insects, mites, etc. As a general 

 rule they are observed upon foliage and grass but many of them are 

 confined to restricted habitats and others appear to he very local in 

 distribution. Certain genera are found almost entirely on the trunks 

 of trees and may be collected most easily by placing the mouth of the 

 killing bottle over them, wliile others occur in large numbers on small 

 flowers, notably Prunus virrjiniana. A few genera are found only 

 along the seashore where they dart about among the pebbles, feeding 

 upon small insects or upon freshly killed invertebrates. 



The mating habits of the Empida; are extremely interesting, but 

 no more than mention of them can be made here. In some cases the 

 males capture ])ivy and use this food as a lure to attract the females. 

 Sometimes the females devour the offering or it may be discarded as 

 soon as the mating is completed. In other cases the male provides a 

 balloon like liulible to attract the female. In some cases it is l)elieved 

 tliat copulation cannot be completed unless food is provided. 



Tlie immature stages are not well known but the larvae live in 

 decaying vegetation, under bark, and in streams. 



