STEATODA FULVA (THERIDIIDAE) , A SPIDER 
THAT FEEDS ON HARVESTER ANTS* 
By Bert Holldobler 
Harvard University, Biological Laboratories 
Cambridge, Massachusetts 02138 
In his revision of the spider genera Crustulina and Steatoda 
H. W. Levi says of the Steatoda fulva- group [ Steatoda fulva (Key- 
serling) ; S. medialis (Banks) ; S. pulcher (Keyserling) ] : “Virtually 
nothing is known of the natural history of these three species” 
( 1 957, P- 387)- T he present paper places on record some preliminary 
observations on the feeding behavior of Steatoda fulva , which were 
made during the course of field experiments with ants in April 1970 
near the campus of the University of South Florida, Tampa. 
The study area, a field of 135 m 2 , contained 54 nests of the 
harvester ant Pogonomyrmex badius (Latreille). The nests were 
uniformly distributed throughout the area. They are excavated in 
the soil; the nest opening is located in the center of a flat sand 
crater (Fig. 1). On 10 occasions webs of Steatoda fulva were found 
in front of the nest entrance. Observations throughout the day 
showed that the webs were probably built and occupied only during 
the afternoon. The webs were attached to dry grass stems around 
the nest entrances and contained from 2-6 trapped ant workers when 
found (Fig. 2). The fact that Steatoda fulva is able to build its 
web so close to the nest entrance is surprising because the ants are 
constantly running in and out of the nest and react aggressively 
to any foreign animal. However this is understandable when one 
compares the activity of the ants on a hot day with the timing of 
the spider’s predatory behavior. During April the Pogonomyrmex 
began to open the nests about 8 AM. Movement to and from the 
nest soon increased, reaching its maximum between 11:00-12:00 
AM, then decreased and by 14:00 had ceased almost completely. 
Generally nests became active again about 1 5 :00, reaching a second 
maximum about 17:00. The ants returned to their nests before 
sunset and outside activity had ceased by 19:00 (Fig. 3). Apparently 
it is during the early afternoon, when temperatures are high and 
the ants are inactive, that Steatoda fulva is able to approach the nest 
entrance. Ant nests that are blocked by a spider’s web show no 
* Manuscript received by the editor, August 3, 1970. 
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