156 
Psyche 
[June 
ders in Panama build much more ephemeral webs that are more 
susceptible to damage (they are nothing like as strong). They prob- 
ably spend much less time on their webs at any one site, a situation 
which may be less favorable to the development of a protracted 
association. The fact that the only time we have seen milichiids 
resting on an Argiope was when this spider had been placed on a 
Nephila web could indicate that the flies respond to some char- 
acteristic of the web in finding their hosts. On a recent trip to 
Papua New Guinea (May 1977), one of us (MHR) looked at over 
500 adult Nephila maculata, hoping to find flies resting on the spi- 
der. None were found. Bristowe (1941:369) reports that R. N. 
Champion Jones saw a small fly crawl over the palps of Nephila 
maculata in India. Conceivably this is a case where a less sustained 
association has evolved. 
As far as the milichiids are concerned it is at least possible that 
their relationship with Nephila may be more than a trophic one. 
The fact that all the Phyllomyza sp. that we collected were females 
is disturbing. The fact that we found Conioscinella feeding on the 
prey of Argiope argentata makes it possible that the egg parasites 
of araneids could also be commensals. The reverse could be true. 
There is some problem about finding terms that accurately de- 
scribe the relationship of the milichiids to their host(s). They are 
clearly commensals (in the broad sense) since they “share a table” 
with their hosts. However, they rely on the host liquifying the 
prey, they drink alongside the host and could perhaps be called 
bibiocommensals. The presence of fairly large numbers of flies 
feeding on a prey item could reduce the amount of food available 
to the host in a significant way, in which case the term parasite 
would be justifiable. A drinking parasite would be a dipsoparasite 
and this term is (to us) more euphonious than bibiocommensal. 
Acknowledgments 
We thank the Insect Identification and Beneficial Insect Intro- 
duction Institute, USDA, Beltsville, Maryland (Chairman, Dr. L. 
Knutson), for identifying all the insects involved in this study. The 
experts involved were: C. W. Sabrosky, J. L. Herring, and S. W. 
Batra. Dr. Sabrosky drew our attention to a number of published 
works on the relationship between milichiids and spiders; this ad- 
ditional help is greatly appreciated. 
