118 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



in New Guinea resting in pairs on the back of an asilid fly, Omma- 

 tius minor Dol. "They sat on the back of the large fly, be- 

 tween the wings, back to back, so that one of them faced toward 

 the head of the robber-fly and the other toward the abdomen." 

 That their occurrence in this manner was not accidental, Biro 

 determined by further observations. In eight additional cases 

 he found the small flies, as before in pairs and back to back, 

 upon the thorax of the asilid. 1>2 This strange association of 

 these minute flies with the large robber-fly appeared quite mys- 

 terious without further knowledge of the habits of the genus. 

 Shortly afterward Joseph Mik, in Austria, found a little swarm 

 of Desmometopa m-atrum upon the body of a freshly killed worker- 

 bee dangling on a spider-thread. The bee apparently had been 

 just killed by a spider and the little flies, thirteen in number, 

 were eagerly probing about on the body of the bee, pushing their 

 horny probosces among the body-hairs and in particular probing 

 about the roots of the wings. Mik observed them in their occu- 

 pation for fully fifteen minutes, before gathering them in, and 

 compared their behavior to that of vultures about a cadaver. 3 



The explanation naturally suggested by this second observa- 

 tion is th,at the Desmometopa found riding on the back of the 

 robber-flies by Biro through this association assured them- 

 selves of suitable food. Later observations, made by Biro dur- 

 ing a short stay at Amboina, confirmed this conclusion. It 

 seems worth while to give his interesting account in his own 

 words, and to let his other observations on the subject follow. 



"In the afternoon hours I withdrew into a young woodland, 

 where first of all Ommatius minor caught my eye, as it fluttered 

 before me from one dry twig to another. Naturally from now on 

 I gave it my undivided attention. 



"From a distance of a few paces we had taken sharp cognizance 

 of each other. The Ommatius was not resting empty-handed, 

 but held between its claws the dead body of a trigoniid cricket; 

 I could not detect his riders. Although quite close, I neverthe- 

 less took out my opera-glasses and began to observe him through 

 them. Thereby I found at once the solution to this apparently 

 strange association. I immediately detected the Agromyzo 

 [ = Desmometopa], and moreover three of them, as they were 

 probing about the prey. Agromyza minutissima is therefore the 



1 Kertesz, Koloman. Uj-Guinea L6gy-Faundjdb61. Dipterologisches 

 aus Neu-Guinea. Termesz. Fiizetek, vol. 20, p. 611-613. 1897. 



2 Bir6, Lajos. Asilida cs lovasa. Rovart. Lapok, vol. 4, p. 129. 1897. 



3 Mik, Josef. Merkwiirdige Beziehungen zwischen Desmometopa M- 

 atrum Meig. aus Europa und Agromyza minutissima v. d. Wulp aus Ncu- 

 Guinca. Wien. Ent. Zeit., vol. 17, p. 146-151. 1898. 



