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Delena cancerides, the spider of "Arachnophobia"

by David Rowell

(This message was originally sent to the Arachnology Mailing List by David Rowell)

Delena cancerides (Sparassidae, or Heteropodidae if you like) is found pretty much all over Australia, wherever there are suitable trees. It is the only social sparassid reported, and can live in colonies of up to 300 spiders under bark. Adult females can have a leg spread exceeding 14cm.

Delena cancerides has been well characterised chromosomally and allozymically, and is particularly unusual as it possesses a number of distinct chromosomal races that differ by carrying different combinations of chromosomal fusions. This is a useful marker as it has made it possible to determine from where in Australia New Zealand's "Avondale spider" originated. Several of the chromosomal races can hybridise and produce fertile offspring, resulting in distinctive hybrid zones. In the best studied of these, animals can have anything from 22 to 43 chromosomes and produce viable sperm.

I have students currently studying the social behaviour of this species as it is particularly unusual. It is one of only 2 social spiders reported which do not build a web snare, and it shows marked intercolony aggression. Very little is known about its dispersal and mating system, however it is clearly outbreeding, as it is among the most allozymically polymorphic (and heterozygous) of all spiders - in contrast to other social spiders, which tend to show very low heterozygosity levels. It's hard to understand how outbreeding is facilitated, given that colonies tend not to tolerate the presence of individuals from other colonies.

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