OF WASHINGTON, VOU'ME XVII, 1915 !!!> 



rommeiisalist of Ommatius minor! The insects hopped nimbly 

 about the body of the cricket, stopped to feast, ran up onto the 

 back of the robber-fly and again descended to the branch, ran 

 and flew rapidly about, and could not rest for a minute. 



"It still remained for me to check the correctness of my ob- 

 servations. Afterwards I amused myself for hours, partly with 

 these first associates, partly with others found in these woods, 

 where (h/nnnthis was far from being a rarity. 



"In the woods of Amboina I captured the whole of one of these 

 partnerships, then first released the Agromyzas, and afterward 

 the Ommatius. It was easy to recapture the robber-fly, as it 

 soon settled again at a distance of fifteen or twenty paces, and, 

 although now more shy, I could, with sufficient patience and 

 equipped with a long-handled net, recapture some individuals 

 three 1 or four times. To my astonishment the little flies had 

 again all congregated upon its back. 



"I still wanted to determine whether these were always the 

 same individuals of Agromyza. For this reason I drove a speci- 

 men into the tip of the net and with the forceps tore a minute 

 piece from its wing; made recognizable in this manner, I per- 

 ceived that it came back twice, although upon the second instance 

 I had released it at a distance of ten or twelve paces. After- 

 wards I facilitated the experiment by simply tethering the 0t- 

 nuitius to the end of a twig. 



"However, not every Ommatius has its companion flies; many 

 Forage about without them. Some harbor only one, some two 

 or three flies, but never more. 



'The fidelity of the Agromyza is praiseworthy. It does not 

 easily change its host. I tethered some robber-flies caught 

 flying about unaccompanied to a branch and then released near 

 them some of the little flies whose host I had killed. All scattered 

 and none adopted the host selected for them." 



As will be seen from the foregoing, Biro was not aware that the 

 flies he had found associated with Ommatius belong to the genus 

 Desmometopa, but they reminded him vividly of the Desmometopa 

 which he had observed repeatedly in southern Europe. When 

 collecting he had never found Desmometopa alone, but always 

 about the prey of some predaceous insect that had just captured 

 a bee, wasp, fly or butterfly. He was first of all impressed by 

 the fact that these little flies showed no fear of spiders, but, on 

 the contrary, boldly participated in their meals. Later he often 

 saw them associated with flower-inhabiting spiders (Misumena 

 arid Thom-isus), as well as with Asilidu*. 



"Most frequently I found them in the region of Fiume and 

 Buccari at the time when Palum* nciilcntux blooms. The flowers 



