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references cited above. In each case, it is feeding on a honeybee. 
According to O’Toole (1978), D. sordida is also phoretic on 
honeybees. 
Clumping could also result from a simultaneously emerging 
brood that locates a host near the site of eclosure. The presence of 
two species, Neophyllomyza A and B, in the instance where five flies 
were found on one prey is not supportive of this explanation. Two 
species of Swedish milichiid kleptoparasites have also been taken 
from the same prey (Lundstrom 1906 in Knab 1915). 
The distribution of the sexes 
All of the flies taken on spider prey or in baited traps were female. 
Nearly all kleptoparasites mentioned in the literature are female as 
well. Among Diptera, the female usually takes more animal food 
than the male (Downes 1971) or ingests such food exclusively. 
Concentrations of females, however, might be expected to attract 
males. In a number of blood-sucking flies, males are common in the 
vicinity of hosts (Anderson 1974). The marked female bias may be 
due to the fact that females remain near the host while males are in 
transit between sites that might harbor a mate. In scarce, widely 
distributed species, apparently an accurate description of most 
spider kleptoparasites, a spider would be more apt to attract a prey 
item than attract a kleptoparasite. A female kleptoparasite might 
“confidently” wait for prey at a spider; a male kleptoparasite would 
do better to visit several spiders to find a mate. Among phoretic 
kleptoparasites, we have found a single record of a riding male, a 
milichiid, Desmometopa sordida, sitting with a female on the 
pronotum of a reduviid bug (Richards 1953). The unique case 
suggests that mate location can occur on the host. 
As flies become more numerous or hosts fewer, the probability of 
the arrival of new females at a spider increases and it might become 
more advantageous for males to stay near hosts. Didactylomyia 
longimana is apparently the most common spider kleptoparasite yet 
described. While only females are taken on prey, both sexes hang in 
webs. Males of D. longimana are more abundant at these sites than 
males of web-hanging, nonkleptoparasitic cecidomyiids (see Table 
1). No mating was observed but male concentrations in webs suggest 
that males may intercept mates at feeding sites. An alternative 
explanation is that female D. longimana search for food and so 
spend less time on webbing than “fasting” non-kleptoparasitic 
