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Toowoomba trapdoor

Fact Box
Species:
Euoplos grandis (QM)
(Identification derived from the paper: M.G. Rix et al (2019) Austral Entomology 58 282-297 but also see notes below)
Family:
Idiopidae,
formerly Ctenizidae
Body length:
female: 35 mm
male: 26 mm
Habitat:
In a burrow with a neatly fitting door; males wander above ground at night during the breeding season which is autumn
Toxicity:
The venom of this species seems to have low toxicity for humans but males may exhibit an aggressive stance as a defence against potential predators and the female during mating
Euoplos species
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The female
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Closed burrow
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Open burrow
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A verified female
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The male
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Another view
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Male palps
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Male underside

The correct name for the trapdoor spider found in large numbers in and around Toowoomba has changed considerably over the last 30 years and has only been finally resolved in 2019. Initially, it was thought by Main to be Arbanitis variabilis but the photos and description of Aganippe berlandi in Ramon Mascord's 1980 book, "Spiders of Australia", suggested this was more likely to be the appropriate scientific name for this species. However, the Aganippe genus has now been renamed Idiosoma and has a distinctly different eye arrangement.

In a more recent revision of some Eastern Australian Idiopidae Raven and Wishart (2005) transferred to the genus Euoplos some species originally considered to be Arbanitis species. These authors stated that a distinctive feature of Euoplos is that it has a fovea (a groove that runs across the centre of the upper side of the cephalothorax) that is deep and curves forward at its edges whereas the fovea of other idiopid genera is not significantly procurved. The Toowoomba Euoplos trapdoor shares with Idiosoma berlandi the tendency to make thick plug doors when on creek banks or in black soil locations but thin doors woven from dry grass leaves in other places. It differs from I. berlandi in that it lacks a visible pair of sigilla (small depressions) on the upper surface of the abdomen which can easily be seen on I. berlandi.

The Toowoomba trapdoor spider is found widely across the Darling Downs and can tolerate relatively dry open grassland areas, unlike funnel-web spiders. Females rarely leave their burrows but mature males do so to search for mates during autumn and early winter, usually appearing during or after periods of rain. During the early 1990s the author of this website was a researcher at the University of Southern Queensland Toowoomba campus and found it easy to collect quite large numbers of female Euoplos grandis specimens from burrows in the extensive campus grounds but never any males matching the images shown above, which are of a specimen obtained from the black-soil plains to the west of Toowoomba.

This created a conundrum situation because during periods of rain in autumn and early winter students at the residential colleges on campus were frequently 'terrorized' in the evenings by the appearance of literally dozens of brown trapdoor males, all of which had the overall appearance, including the presence of a double spur on Tibia I, typical of most Australian Arbanitis males, including the many species that were once known as Misgolas species. Other Toowoomba residents also brought in for identification many similar specimens of this kind of spider. This was a curious observation because the author found the burrows of Arbanitis/Misgolas species to be present around Toowoomba along some creeks and water courses (for example Arbanitis species) but uncommon elsewhere and certainly not in the University grounds. The fact that the University campus was heavily populated by female Euoplos rather than Arbanitis females but only males of the latter genus emerged in large numbers during the rainy autumn nights was considered inexplicable to the author. It was for this reason the idiopid males and females found in large numbers on the University campus were presumed to be the same species. However, according to the Raven/Wishart 2005 paper this cannot be so.

It is also worth mentioning here that the author milked the venom of these Euoplos females and Arbanitis males and tested them for toxicity in anaesthetized lab rats. The results of these experiments can be found in the following published paper: R.K. Atkinson (1993) "A comparison of the toxicity of the venoms of twelve common Australian spider species on rodent vital organ systems" Comparative Biochemistry and Physiology 106(3) 639-642. Note that in 1993 the Toowoomba funnel-web spider (Hadronyche infensa) was still being called Atrax infensus and the trapdoor spider now listed as Euoplos grandis was believed to be Aganippe berlandi. When venom from each of these species was infused into anaesthetized rats it was found that while funnel-web venom (especially from male spiders) strongly interfered with respiratory and cardiac functions in these rats venom from Euoplos grandis females and Arbanitis males caused very little disruption of the breathing and heartbeat of the rats. On this basis thes Toowoomba species did not deserve to be considered to be seriously dangerous to humans.

Spider(s) with a very similar appearance: Euoplos variabilis flavomaculata, Cataxia spinipectoris, Namea salanitri, Aname barrema and Arbanitis species.


Email Ron Atkinson for more information.    Last updated 12 November 2019.