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Psyche 
[Vol. 87 
attractive interpretation of the data since species of Megaselia are 
known to both attack spider eggs and oviposit on dead insects 
(Bristowe 1941; Disney and Evans 1979). Bristowe (1924) found 
commensal phorids living in the burrows of Brazilian mygalo- 
morphs, where they breed in the remains of the spiders’ meals. 
Discussion 
Proximity between kleptoparasites and hosts 
The results of trapping with spider prey bait show that Didacty- 
lomyia longimana, and perhaps other kleptoparasites, locate food 
by tracking the scents of haemolymph and/or digestive compounds. 
Flies may remain in the vicinity of a spider after eating, or locate 
and stay near nonfeeding spiders, to wait for subsequent meals. The 
above tactics are not mutually excluvive either within a species or 
the repertoire of a single individual. The “decision” to stay with a 
preyless spider or to go might depend on the searching ability of the 
parasite, the danger of travel, and the density of hosts (see Robinson 
and Robinson 1977). Flying Didactylomyia longimana were always 
seen coming towards prey from downwind, but “resting” individuals 
commonly hung on the non-sticky supportive lines of spider webs. 
Such behavior is common in other Nematocera, cecidomyiids and 
tipulids, and is apparently a means of escaping stalking predators on 
foliage (Robinson and Robinson 1976). In a kleptoparasite, the 
duration of hanging bouts might be influenced by host finding 
considerations. 
Among the flies that wait near spiders, competition to reach 
choice feeding sites might favor those individuals who maintain the 
most intimate relationships with their hosts. The degree of intimacy 
between the symbionts depends on the parasite’s ability to overcome 
the formidable dangers of a gargantuan predator and its entangling 
web. The kleptoparasitic empidid Microphorus crassipes is a 
frequent prey of its host (Faurence 1948). Spiders are a major cause 
of mortality in kleptoparasitic panorpids (Thornhill 1978). We 
witnessed a Paramyia nitens become trapped in an Argiope aurantia 
web after being flushed from the prey. McCook (1889) found a 
similar fly “trussed up near the spot where it had lately fed.” 
Some symbionts live in webs but escape entrapment (Bristowe 
1941; Worth 1967; Davis and Russel 1969; McMillan 1975; 
Thornhill 1975). Didactylomyia longimanus was occasionally seen 
