Behavioral Ecology and Sociobiology

, Volume 18, Issue 4, pp 283–287 | Cite as

Eusociality and extraordinary sex ratios in the spider Anelosimus eximius (Araneae: Theridiidae)

  • Fritz Vollrath


Colonies of Anelosimus eximius in Panama had an average sex ratio of 0.15±sd 0.09, i.e. about five females for each male. The sex ratio in egg sacs reared was even lower (0.08±0.01), as was that of immatures in newly founded colonies (0.12±0.05). The possible mechanisms responsible are discussed. Mature colonies had an average ratio of 17 females and 2 males for each egg sac present (range: 2–91 females, 0.2–8.2 males) and contained a large proportion of females which were not inseminated but which presumably ‘help’. Since both sexes are diploid, arrhenotoky can be ruled out and it is assumed that some females do not come to reproduction, the proportion depending on the availability of resources. This mechanism may enable entire colonies to survive lean times.


Average Ratio Entire Coloni Mature Coloni Lean Time 
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Copyright information

© Springer-Verlag 1986

Authors and Affiliations

  • Fritz Vollrath
    • 1
  1. 1.Smithsonian Tropical Research InstitutePanama

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