Written by Joe Ballenger
Your Name: Mark
Your Bug Question: I have spiders in and around my house. I eventually get around to removing their webs from hard to reach places like living room chandelier. It takes so long that i doubt I ever bother the same spider twice. Yet after a year or so the spiders seem to know not to build webs on the chandelier. It is as if they could be passing their learning along to other spiders. That seems unlikely, but I cannot come up with a better explanation. Can you explain what is happening?
I found this question interesting, because it’s really two questions in one. The first, is whether disturbance influences where spiders build webs. The second, and more interesting, is whether this information can be transferred between different spiders of the same species.
The answers to these questions depends on the ID of the spiders in question, and there are several species of web-building spiders which can be found in houses. The most common species found in homes, Pholcus phalangoides, is the one I’ll focus on. Not only is it the most common, I think it gives the best answer to the question because of it’s life history.
Pholcus phalangoides, more commonly known as the ‘cellar spider’, is actually a very interesting spider. It’s semi social, with juveniles sometimes cooperating to build webs. It’s also a pirate, frequently taking over the webs of other spider species after eating the occupants.
So let’s explore this idea, because it’s interesting territory.
Life History of Cellar Spiders
I think the first thing we should do is talk about how this spider lives, because that will guide the answer to this question.
Cellar spiders like to live in cool, dry, undisturbed environments. Their natural habitats are caves, and cave-like structures in the wild. They’re very hardy, and don’t need a whole lot in the way of food or water. They are very well adapted to human dwellings, and feed on the occasional insects which stumble into our homes.
I wasn’t able to find a whole lot about the life history of this species. Most of the work that’s been done on this spider is about sexual competition, and social behavior. I did find some papers indicating that development takes a little under 5 months, depending on food availability.
Most spiders are relatively short lived, at least compared to tarantulas. The typical lifespan of a non-tarantula spider is about a year, which kind of fits with the narrative of the question.
Do Social Spiders Communicate?
Sociality in insects is…complicated. Some insects are highly social, and others aren’t. In highly social insects, information is transmitted between individuals. Honeybees, for example, are particularly good at this. They can communicate everything from the health status of the queen, to the location of food.
Spiders are different, though. A lot of spider sociality seems to be self-organizing cooperation. They tolerate each other, help spin and maintain the web, and help coordinate to capture prey. Each of these activities does require some amount of communication, but nothing as complex as what we see in the video above.
There’s also a lot of antagonism in spider colonies, which you see in less developed insect societies. Spiders in colonies will fight between themselves over feeding sites on the prey, and even food sources…behaviors you don’t see in honeybee colonies. You see this somewhat in wasp colonies, but it’s not as pronounced as it is in spider colonies.
Cellar spiders, when they decide to live in groups, seem to be very loose-knit. They’ll feed communally, and build webs, but there isn’t really any evidence of communication between groups of different spiders.
As an aside, a lot of social spider species do display some very complicated behaviors. Some of the behaviors in the literature seem to be a lot more complicated than simple self-organization, and I wouldn’t be surprised if spider communication is more complicated than is thought at the current time. However, the behavior of cellar spider colonies in particular does seem to be explained very well by self-organized cooperation.
Do Spiders Choose Their Nest Sites Based on Disturbance?
Every arthropod species which has been examined seems to have some capacity for learning, although that capacity may be dependent on the group’s habits. Jumping spiders, which routinely tackle prey that’s large and dangerous, seem to be good learners. No studies on learning seem to have been performed on anything closely related to cellar spiders, but I’d be surprised if they didn’t have the ability to change their behavior in response to their environment.
Spiders like to build their webs in specific habitats, and they will change where they build their webs based on how often it’s destroyed. Silk is very expensive to make, and building a web takes time. If a spider isn’t in their web, they’re also at risk of being eaten. If you’re a spider, it pays to be very careful when choosing a nest site. Spiders choose their nest sites very carefully, and things like food availability and disturbance are a large part of the decision about where to build a home.
The Bottom Line
Here’s what I think is happening, based on what I know about cellar spiders, spider colonies and arthropod learning in general.
First, cellar spiders will take over old webs. By removing the webs, Mark is depriving spiders of already-made resources and making it more difficult for them to colonize new areas. Younger spiders may prefer to hang out in ready-made webs, and webless areas may be less attractive to the spiders.
As Mark is knocking the webs down, it’s also possible the spiders are learning which environments in the house are most often disturbed through the process of trial-and-error. Although this sort of habitat searching hasn’t been documented in cellar spiders, it has been documented in a wide range of web-building spiders. I think it’s very likely it happens in cellar spiders as well.
New cellar spiders occasionally come into the house, through birth or immigration, and wouldn’t have knowledge of which areas are disturbed less frequently. Because they’re not familiar with the habitat, naive spiders may attempt to build webs in the highly disturbed environments. It’s also possible that older spiders are pushing younger spiders out of the webs, and they’re looking for places to build new webs because of a lack of unoccupied webs.
So there are at least two possible explanations for what’s going on here. The first, cellar spiders preferring pre-webbed areas, is what’s most strongly supported by the literature. The second explanation, spiders learning that some areas are more disturbed than others, is inferred from habits of other web building spiders. Personally, I think both options are playing roles here.
I’m not sure that communication between individuals is needed to explain the sort of sporadic web-building behavior that Mark is observing.
Nice one. There is a 3rd possible explanation. A lot of spider communication is done via chemical signaling. These cues, often transmitted trough silk, can tell a spider a lot about the features of the spider, that left them behind – species, sex, age, body condition, mating status.. As Pholcus phalangoides is a cannibalistic spider it is imaginable, that they actively avoid locations where there are cues from conspecifics, that might be dangerous to them (e.g. older and bigger and anyways not in the mood to mate). Predator avoiding behaviour that relies on cues of the predator is known for a number of species.
So if Mark did just wipe the webs away but did not properly clean the whole chandelier, there are surely chemical cues from the spider left.
Btw, I work on permanently social spiders (Stegodyphus dumicola) and so far I did not get the impression, that they have a complex communication system exceeding chemical cues and vibrational signalling during prey capture. Although I have to admit, that I do not explicitly work on that topic. But I don´t think they are able to actively communicate and learn from each other. Maybe just in indirect ways, e.g. if you train a spider to accept certain prey that the rest of the colony does not know and does not react to. The rest of the colony will learn that the new vibrational signal means food as well I guess, following the attacking attempts (which produces certain virbrations in the web) of the trained spider and getting the positive response of food. But on the other hand, if the trained spider would be the only one knowing a certain vibrational signal means danger, it would not be able to tell its colony members. They would need to find out themselfs.
Interindividual learning should be even more unlikely in non-social species like Pholcus.
all the best,
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