Spotlight on urban wildlife: Daddy-long-legs spider Pholcus phalangioides
  • Last updated:
  • 08 Mar 2019

If you thought carrying a human foetus around required a marathon effort from the mother (and after around 36 weeks gestation it does!), spare a thought for the dedication of the slender female daddy-long-legs spider, Pholcus phalangioides. This splendid little ‘Mother of the Year’ not only clutches a sac of up to 50 eggs in her pedipalps for the 17-24 day incubation period, but she continues to carry her bundle of spiderlings for another week or so until they disperse into her web and then beyond. 

Although the daddy-long-legs is one of Australia’s most common and frequently seen spiders, it isn’t native to Australia and was accidentally introduced to this country from Europe many years ago. The average life span of an adult daddy-long-legs can vary from 223-774 days and in that time the female may produce from two to eight egg sacs containing a mix of fertilised and unfertilised eggs. Studies have found that the interval between batches and the number of unfertilised eggs per batch both increase as time progresses in the breeding season.

There are two well-known daddy-long-leg urban myths that have been quite durable across a number of years: 1- the daddy-long legs is extremely venomous, and 2- its fangs cannot penetrate human skin. On the first, research has shown that daddy-long-legs venom is actually not exceptionally potent, even to insects. On the second, if it chooses to inject its venom into human skin it has the capacity to do so - a result that was famously demonstrated on an episode of Mythbusters in 2004. Its exaggerated notoriety as a highly venomous spider may have arisen after being observed preying on other well-known arachnids, including the redback spider Latrodectus hasselti and the grey huntsman Holconia immanis. However, what it lacks in venom potency is compensated for by its hunting versatility.

Individual daddy-long-legs can be both web builders and web invaders. In addition to hanging about in its own web, it has been recorded invading the webs of other species, where it will eat the owner of the web, any prey it had in its web, and its eggs if they happen to be there as well. Interestingly, the daddy-long-legs builds a non-sticky web, which does make one wonder how it fares when it invades the web of a sticky-web builder. It actually has two amazing tricks up its sleeve. The first is the use of its long spindly legs to tiptoe across the tacky threads, thereby minimising contact with the sticky web. The second trick is to lay down a ‘path’ of its own non-sticky web over the resident spider’s sticky thread, effectively creating its own non-stick pathway.

While the female is solely responsible for the care of eggs and protection of young, it is the male who takes the lead in courtship and mating. In what human females might perceive as downright annoying behaviour, the male initiates courtship with four consistent actions: abdominal vibrations, tapping the female’s web, jerking the web and tapping the female’s legs. He will then, not surprisingly, approach the female very cautiously for coupling. If he doesn’t get this right quickly the female will drive him away or he will retreat and try again with the same routine, minus the abdominal vibration behaviour. The female can occasionally eat the male if he’s not up to scratch, but this behaviour is quite rare in daddy-long-legs spiders. In fact, it appears the female’s tolerance might be quite high, with one researcher recording a lack of any type of response from one female even after an hour of spirited leg tapping from a male.

Even the most frequently seen animals can reveal surprising behaviours if you take the time to study them.  This is certainly the case for this ubiquitous little spider that is completely at home in our homes. Look in quiet corners or under the furniture in almost any home and you will find this amazing little arachnid courting, mating, raising young and generally forming part of the complex ecology of urban habitats.

Article by Julie O'Connor SCC Conservation Partnerships Officer 

References 

Bartos, Maciej, 1998, Quantitative analyses of male courtship behaviour in Pholcus phalangioides in P. A. Seldon (ed) (ed.) Proceedings of the 17th European Colloquium of Arachnology, Edinburgh 1997.