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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