A KLEPTOPARASITIC CECIDOMYIID AND OTHER 
FLIES ASSOCIATED WITH SPIDERS 
By John Sivinski 1 and Mark Stowe 2 
Spiders and their webs are predictable sources of insect cadavers. 
A small number of animals regularly exploit this resource, either as 
kleptoparasites or commensals, depending on whether symbionts 
compete for the same prey (see Robinson and Robinson, 1977, for 
more detailed terminology). Among the thieves are specialized 
spiders (citations in Vollrath 1979a, 1979b), mature male and 
juvenile spiders (Stowe 1978, citations in Nyffeler and Benz 1980), 
Hemiptera (Davis and Russell 1969), a hummingbird (takes web¬ 
bing in addition to small insects, Young 1971), panorpid scorpion- 
flies (Thornhill 1975), Lepidoptera larvae (Robinson 1978), wasps 
(Jeanne 1972), damselflies (Vollrath 1977), and a handful of flies 
(reviews in Knab 1915; Bristowe 1931, 1941; Lindner 1937; Richards 
1953; Robinson and Robinson 1977). Only a few of the reports on 
Diptera kleptoparasites originate from North America (McCook 
1889, Frost 1913, Downes and Smith 1969). With a single exception 
(Downes and Smith 1969), all of the previously described klepto- 
parasitic flies belong to the Brachycera and Cyclorrhapha. We 
report here on a surprisingly diverse kleptoparasitic Diptera fauna 
in north central Florida with a cecidomyiid (Nematocera) as its 
dominant member. 
Methods 
Unless otherwise noted, specimens were taken in Alachua County, 
Florida, during August and September, 1980. Observations were 
made principally at night, using red filtered light. A trap was 
constructed to test whether flies were attracted to dead insects in 
general or those partially digested by spiders in particular. Trans¬ 
parent plastic discs (10 cm. dia.) were covered on one side with 
Tacky Trap®, a trapping compound. Three discs were strung 
between bamboo poles and placed near a web of Nephila clavipes (a 
'Department of Entomology and Nematology, University of Florida, Gainesville, 
Fla. 32611 
"Museum of Comparative Zoology, Harvard University, Cambridge, Mass. 02138 
Manuscript received by the editor May 13, 1981. 
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