The Two-winged Flies 335 
or other vegetable matter, are also probably predaceous, feeding on smaller 
insects living in the same places. 
The commoner species that dance in large swarms belong to the genera 
Empis and Rhamphomyia (Fig. 470). The males of certain species of Empis 
and Hilara have the odd habit of blowing out bubbles of a whitish viscid sub¬ 
stance which they carry about with them in the air. It is believed that these 
toy balloons are attractive to the females. At least, Professor Aldrich, a 
well-known student of flies, has seen a female choose that male among several 
which was carrying the largest balloon I 
An attractive lot of small slender flies, usually of iridescent green or 
greenish-black or blue color, with 
unusually long slender legs, are 
the Dolichopodidae, or long-legged 
flies. They are found especially 
in marshy or low places where 
vegetation grows lush and rank. 
They flit about searching for 
lesser insects, which they catch 
and devour. They often get their 
prey by swift chasing over leaves or ground or even on the surface of water. 
Like the Empidids the larvae are also predaceous, living underground or in 
decaying vegetable matter. Some have been found in the exuding sap of 
Fig. 471. — Diagram of wing of dance-fly, 
Rhamphomyia sp., showing venation. 
Fig. 472. Fig. 473. 
Fig. 472. —Mouth-parts of dance-fly. Rhamphomyia sp. lb., labrum; mx., maxilla; 
mx.l., maxillary lobe; mx.p., maxillary palpus; li., labium; hyp., hypopharynx. 
Fig. 473 .—Dolichopus lobatus. (Three times natural size.) 
trees and elsewhere on or under bark. The larvae of certain species spin 
little thin cocoons when ready to pupate, but with most the pupa is 
naked. 
