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Dr Volker Framenau answers your questions

Dr Volker Framenau is one of Australia’s leading arachnologists and has significant research experience in the taxonomy and systematics, population biology and behavioural ecology of spiders and other arachnids.

Here he answers your questions about fire and funnel webs.

 

Spiders and fire

Denise asks:

I live at Darwin River, about 80 kms southwest of Darwin, NT.  Gamba and Mission Grass are out of control in this area, although landholders like myself are doing our best to contain it.

Has there been any research on spiders, particularly Selencosmia spp. and fire? Are they adversely affected by too frequent or destructive fires?

Volker answers, with some assistance from Dr Robert Raven from the Queensland Museum:

Fire is an important factor shaping the Australian landscape and it is therefore not surprising that there is an abundance of scientific literature dealing with the effects on fauna and flora. However, there is a paucity on studies on spiders and their response to fire in this country. Different mygalomorphs and indeed many araneomorphs respond to fires in different ways in different parts of the country. We have no clear rule of thumb yet.

One notable exception to this knowledge gap is the recent Ph.D. research of Peter Langlands in Western Australia. Peter generally studied community-level changes and also analysed if certain traits of spiders correlated with fire resilience. I have listed his studies below.

Peter additionally set out to investigate the effects on populations of a large mygalomorph spider in the genus Gaius (family Idiopidae), not quite a large as Selenocosmia or other members of the Theraphosidae, but not too far behind. However, from memory, Peter’s fire experiments did not provide sufficient and reliable data to interpret differences in survival rates of Gaius with or without fire.

Ultimately, these studies require a very long-time approach (taking the longevity of large mygalomorph spiders into account) and appropriate analyses of the survival rate of different life stages within a fire-affected population. You can imagine, that the deep-burrowing females may be little effected even by a very hot fire, but dispersing immatures with shallower burrows may not survive.

One very interesting study on fire and invertebrates was that by Karl Brennan and colleagues who set individual grass trees (Xanthorrhoea) on fire in Western Australia to test if plants with tightly packed leaf-bases provide a refuge for invertebrates during fire even when the plants themselves burn. They found that species-specific microhabitat preferences within the plant appeared to influence survivorship. Species collected in the crown of unburned plants were found more often alive on burnt plants than species typically inhabiting the dead skirt of decaying leaves.


A male Giant Trapdoor Spider (Giaus sp.). Image: V.Framenau.

Overall, there is still a lot to learn about wildfires and fire in this country!

You can read more in these references:

Langlands, P.R., Brennan, K.E.C. & Pearson, D.J. (2006) Spiders, spinifex, rainfall and fire: long-term changes in a community of desert spiders. Journal of Arid Environments 67: 36–59.

Langlands, P.R. (2010) Conservation of Spiders (Araneae) in the Western Australian Rangelands, with Particular Reference to Disturbance by Fire. PhD thesis. University of Western Australia, Perth.

Langlands, P., Brennan, K. E. C., Framenau, V. W. & Main, B. Y. 2011. Predicting the post-fire responses of animal assemblages: testing a trait-based approach using spiders. Journal of Animal Ecology 80: 558–568.

Brennan, K.E.C., Moir, M.L. & Wittkuhn, R.S. 2011. Fire refugia: the mechanism governing animal survivorship within a highly flammable plant. Austral Ecology 36: 131–141.

Sydney spider hole?

Alan asks:

I have a property in the rain forest 40 odd k's west of Wauchope. I have noticed a large number of holes with funnel webs around the edge of the house. and when I go out after dark with a torch the holes are occupied with spiders . My question is, are these spiders the same as the Sydney funnel web (and just as venomous) or are they a different species? There are a number of different spiders around the area; you hear stories from the locals of some unusual types they come across during their farming activities.

Volker answers:

There are a number of spiders that construct burrows with funnel-shaped webs at the entrance, including the Funnel-web Spiders (family Hexathelidae) that include the notorious Sydney Funnel-web Spider, Atrax robustus. This species occurs in a radius of around 120 km around Sydney. However, there are other species and genera in the family Hexathelidae known from Australia and the most venomous are members of the genera Atrax and Hadronyche.

Severe Funnel-web Spider bites (or envenomation) have generally only been reported from Queensland and New South Wales and the most common culprits are A. robustus and the two Tree Funnel-web Spiders Hadronyche cerberea and H. formidabilis. Hexathelidae only occur in the eastern states and have never been reported from Western Australia. Burrows of Hexathelidae, in particular A. robustus, are generally built at shaded places such in gullies in forests and are rarely found around houses.

Other spiders with funnel- or sheet-web like retreats include, for example, the members of the Stiphidiidae, which includes the Platform and Sombrero spiders with massive sheet-webs that have a funnel-lice retreat. The Black and Brown House Spiders, Badumna insignis and B. longiqua (family Desidae) also construct a funnel-shaped web which can extend quite a bit from the retreat.

These are the most likely candidates for your inquiry. Based on the description, I cannot say what spider you are concerned about, and it would be best to take an image of the web and possibly spider to further shed light on the spiders.