ARGYRODES ATTENUATUS (THERIDIIDAE): 
A WEB THAT IS NOT A SNARE* 
By William G. Eberhard 
Smithsonian Tropical Research Institute 
and 
Escuela de Biologia, Universidad de Costa Rica, 
Ciudad Universitaria, Costa Rica 
Introduction 
Spiders of the large theridiid genus Argyrodes, whose natural 
history was reviewed by Exline and Levi (1962), seem to have 
generally abandoned the usual theridiid habit of spinning webs to 
capture insect prey. A few spin their own webs, but more often they 
live in the webs of other, larger web-building spiders where they 
remove prey from the host’s web (e.g. Kullmann 1959, Vollrath 
1978). The apparently kleptoparasitic species A. trigonum ( trigon- 
um species group) actually preys on its hosts on occasion. 
Argyrodes species in the Rhomphaea group have also been found 
feeding on web spiders, but some in circumstances which suggest a 
strict predator-prey relationship rather than kleptoparasitism. 
Exline and Levi (1962) note two observations of A. (R.) fictilium 
preying on web weavers although fictilium “often make small 
theridiid webs of their own”. I have found an A. (R.) projiciens 
(O.P. Camb.) feeding on a Metazygia sp. which leaves its web up 
only during the night, thus making kleptoparasitism unlikely; the 
state of the prey’s web indicated that it was attacked as it was 
building its web early in the evening. 1 have also seen an unidentified 
species feeding on an Araneus (?) sp., a species which leaves its web 
up only two to three hours in the early evening and then removes it 
completely. 
Clyne (1979) showed that a species from the Ariamnes group, 
Argyrodes colubrinus, uses still another tactic. These spiders also 
specialize on spider prey, but attack ballooning mature male spiders 
which walk onto their webs of long, non-sticky threads. Roberts 
(1952) notes that A. (A.) flagellum also spins a web consisting of 
only a few long, very fine theads; perhaps mistakenly he states that 
the lines are sticky. 
* Manuscript received by the editor February 15, 1980. 
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