Impact of predation upon honey bees (Hymenoptera, Apidae), by orb-weaving spiders (Araneae, Araneidae and Tetragnathidae) in grassland ecosystems.
1991
Nyffeler M. | Breene R.G.
Estimates of predation on the honey bee, Apis mellifera L., by a guild of orb-weaving spiders were made in two different habitats in central Europe. In the first habitat, an abandoned grassland (megaphorbe meadow), honey bees comprised 1 per cent (by numbers) of the 7480 prey items collected from orb-webs between May and September. Approximately 99 per cent of the 72 observed cases of predation on honey bees took place in the second half of summer (August-Spetember), when the three large orb-weaver species Argiope bruennichi (Scopoli), Araneus quadratus Clerck, and Araneus diadematus Clerck reached full size (matured) and build large, strong (ca. 25 cm diameter) webs. Predation by these spider species on honey bees in the first half of summer was apparently insignificant (only 1 per cent of observed predation events), probably due to their relatively small web and body size. Based on sampling counts of the number of web per square metre and the number of bees intercepted per web, we estimated that the spiders' prey kill per square metre in the grassland averaged 1 honey bee every 4th day in August, and 1 every 5th day in September during rain free periods. About 95 per cent of observed orb-weaver predation was attributable to A. bruennichi and A. quadratus, while 5 per cent was due to A. diadematus. The second estimate was made in another grassland habitat, heavily infested with the thistle Cirsium arvense (L.), in the same geographic area. Honey bees comprised 15 per cent (by numbers) of 215 prey items collected from webs of the dominant orb-weaver species (A. bruennichi) during August-September. We estimated that the A. bruennichi population may have killed approximately 1 honey bee per square metre every 5th day in August during rain free periods.
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