A FLY THAT MIMICS JUMPING SPIDERS* 
By Thomas Eisner 
Section of Neurobiology and Behavior 
Cornell University, Ithaca, NY 14853 
On August 3, 1984, in the course of field work near Portal, 
Highlands County, Arizona, I caught sight of a gaudily-colored 
tephritid fly, which at first completely fooled me into believing it 
was a jumping spider. Subsequently caught and identified as Zono- 
semata vittigera, it had been resting on a leaf of its larval food plant 
(Cazier, 1962), the white horse nettle Solatium elaeagnifolium. 
Rather than taking instantly to flight in response to my approach, it 
moved about erratically over the leaf, or in short darting flights 
from leaf to neighboring leaf, in patent imitation of the close-range 
evasive maneuverings of jumping spiders. What made the mimicry 
uncanny was the fly’s seeming predilection during moments of rest 
of presenting itself in rear-end view (Fig. 1). Thus oriented, with its 
abdomen masquerading as a prosoma (complete with eye spots), its 
thorax plus head as an opisthosoma, and the dark bands on its 
wings as a set of legs, it took on a distinct spider-like appearance. 
The overall aposematism, so characteristic of jumping spiders, 
completed the imitation. The fly’s abdomen is orange (evenly 
colored, like many a jumping spider’s prosoma), and its thorax 
yellow and black (mottled, like many an opisthosoma). Its actual 
legs, irrelevant to the mimicry and potentially distractive from the 
resemblance, are yellowish-green, in line with the background vege- 
tation. Subsequent sightings that I made of the fly were on both S. 
elaeagnifolium and on sunflower ( Helianthus annuus). 
Imitation of jumping spiders could clearly be of benefit to an 
insect. Jumping spiders are hard to catch and capable of inflicting 
poisonous bites, and might thus be shunned by any number of 
vertebrate and insectan predators. 
Other tephritids may show comparable mimicry. Monteith (1972) 
pointed to the similarity in appearance and movement of Rhagoletis 
pomonella to the sympatric jumping spider Paraphidippus margina- 
♦Manuscript received by the editor September 2, 1984 
103 
