Cellar Spiders – As Interesting as they are Common

If, like me, you live in the UK then you will have seen this spider. I am pretty confident that these guys are probably one the most frequently encountered spiders out there, yep that’s right I am talking about the cellar spider (Pholcus phalangioides). If you don’t believe me then go and open your airing cupboard, garage, or garden shed and I guarantee you’ll find one of these spindly spiders. However, being incredibly common, does not make them boring, in fact they display several behaviours that make them particularly interesting. So, I thought I would write a little post about why these common house invaders are one of my favourite species and why they should be a welcomed house guest.

Background

The cellar spider (Pholcus phalangioides), is also sometimes called a ‘daddy-longlegs’ but this is a term that I greatly dislike, due to it being used for so many different organisms (crane flies, harvestmen etc). They belong to the spider family Pholcidae, which is among the most speciose spider families and is comprised of approximately 1500 species (Dimitrov et al., 2013). These spiders are spread across the world and found on every continent apart from Antarctica. Pholcids are well known for their incredibly long legs when compared to their body size and their messy, tangled webs. Whilst they are often overlooked due to their abundance, they exhibit numerous fascinating behaviours.

Spider hunting

Despite their spindly appearance, these thin bodied arachnids are deadly spider hunters. That’s right, even arachnophobes are going to want these guys occupying their homes. There are plenty of araneophagic animals out there, but what fascinates me is the contest between these cellar spiders are your typical “house spiders”, Eratigena atrica (or Tegeneria depending on your phylogenetic stance… a topic for another day). The size difference between these two spiders is substantial and the one you’d expect to be the hunter is the prey. P. phalangioides has a number of attributes and behaviours that enable it to predate on larger spiders. Firstly, it acts as an aggressive mimic. To do this, the cellar spider sits next to another spider’s web and uses its legs to vibrate the web in a way that resembles the vibrations of an ensnared insect (Jackson and Brassington, 1987). As the web’s owner approaches, thinking it has caught itself some dinner, the P. phalangioides attacks. Its long, thin legs, do not give the spider a lot to attack and enables the cellar spider to keep its body out of reach of counter attack. Their first move is often to throw silk at their prey, be it a spider or an insect, before biting. They have been observed hanging from their webs leaving as few as two legs still in contact with the web and ‘throwing’ silk over a prey item that is residing away from the web.

Predator defense                     

However, many of these offensive behaviours are also employed when on the defensive and become particularly important when attempting to take down larger spiders. For example, when confronted aggressively by larger spiders, P. phalangioides is often observed throwing silk at its attacker before making a hasty retreat. Their gangly legs give them a defensive advantage as well and they will often abandon a leg that has been caught by their attacker whilst again making a hasty retreat. It is not uncommon to find cellar spiders with one or two legs missing from their close encounters with their dangerous prey. Furthermore, they exhibit a behaviour known as ‘whirling’ where they whip their small body around in circles, which is thought to aid them in several ways when being predated on. By rapidly moving their body in a circular motion they can potentially appear much larger than they are to their attacker. Further, they become a far harder target to accurately attack. This is particularly necessary because whilst they hunt spider, they are also predated on by other spiders, most notably jumping spiders (Salticids), it really is a spider eat spider world out there. The jumping spiders of the Genus Portia are particularly known for their ability to predate on web building spiders and have been consistently observed feeding on Pholcus phalangioides (Jackson, 1990). Many jumping spiders predate on web dwelling spiders by pouncing on them from outside the web, however Portia jumping spiders invade the web and actually use aggressive mimicry against the cellar spiders. Oh, how the table has turned. Portia jumping spiders made the news not too long ago for their problem-solving abilities potentially being a sign of a level of intelligence that is uncommon in arthropods, but I’ll save that for another post. The point of bringing these Salticids up was that a study has shown that the whirling technique used by the cellar spiders is effective against the attacks from the spider hunting jumping spiders (Jackson, 1990). However, there is a predator-prey arms race between these two spiders because the variety of techniques in the Portia arsenal has resulted in them often being able to avoid detection by the cellar spider until it is too late for it to start whirling (Jackson, 1990). This is what sets the Portia apart from the other spider hunting Salticids.

Conclusion

I may have become slightly distracted at the end there by the behaviours of the jumping spiders, but it was still somewhat relevant. It is fascinating that the common cellar spider which is found across the world and in your own home demonstrate such interesting behaviours both when on the offensive and on the defensive. I find it even more fascinating that another species of spider predates on the cellar spider by employing the same tactics.

I hope that you have enjoyed this post on the cellar spider, it has acted as yet another example of a common species being more interesting than it first appears. Thank you for reading, until next time.

Don’t forget you can find ZoologyNotes on Twitter – Matthew Woodard @ZoologyNotes

References

Dimitrov, D., Astrin, J.J. and Huber, B.A. Pholcid Spider Molecular Systematics Revisited, with New Insights into the Biogeography and the Evolution of the Group. Cladistics, 29, 132-46.

Jackson, R.R. and Brassington, R.J. (1987). The Biology of Pholcus phalangioides (Araneae, Pholcidae): Predatory versatility, araneophagy and aggressive mimicry. Journal of Zoology London, 211, 227-38.

Jackson, R.R. (1990). Predator-prey interactions between jumping spiders (Araneae, Salticidae) and Pholcus phalangioides (Araneae, Pholcidae). Journal of Zoology London, 22, 553-9.