Well, luckily I got to work in the lab quite a bit this week, because it is heating up a lot down here in Texas (and everywhere else it seems). If you’re stuck inside this weekend, spend some time getting to know the spiders in your house/apartment/etc. Or, go to a pool, and see who’s living in the dirt or grass around you. Either way, here are some fun links about spider biology for your enjoyment. Stay cool and have a good weekend!
Did you know that some spiders go fishing for their dinner? (If you haven’t watched it before, the whole Life in the Undergrowth series is amazing. Can we really expect anything less from David Attenborough? Honestly, though, I never thought I would find slug mating to be so beautiful and majestic, but this video completely changed my mind.)
How did I not see this earlier? So cool. (Also, this is a classic, though some dispute the ethics of it all).
Let’s see, what do we know about spiders… They have eight legs right? They’re not insects, but they are sort of related to insects. They’re sometimes called arachnids, but not all arachnids are spiders. We call this a spider. But, we also call this a spider, and they don’t seem to have much in common… And then sometimes we call this a spider (because it looks like one right?), and it isn’t a spider at all! So the question remains: what does it truly mean to be a spider?
Spiders, or organisms in the class Araneae, are certainly highly variable, but they all have a few things in common. First, though, let’s take a look at their higher taxonomic classifications. All spiders are part of the phylum Arthropoda (within the kingdom Animalia, of course), meaning that they are invertebrates with a segmented body, an exoskeleton, and jointed appendages. Spiders hold these features in common with other organisms, including insects, millipedes, and shrimp, that are all classified as Arthropods, as well.
From here, we find that spiders split from these other organisms into a subphylum called Chelicerata. The three groups of organisms in this category (arachnids, sea spiders, and sea scorpions + horseshoe crabs) have a number of features in common, but the name for this subphylum comes from one main feature: the presence of chelicerae. Chelicerae are, essentially, appendages near the mouth of an organism, that are used as fangs or pincers. These are similar to other Arthropod mouthparts, but mostly differ in their morphology/shape.
Arachnids are the largest class in the Chelicerata subphylum, and includes some well-known organisms like spiders, mites, ticks, and scorpions, as well as other lesser-known organisms such as whipscorpions and Harvestmen (The Other Arachnids). They are primarily distinguished from other chelicerates by their four pairs of legs, and one main body division between the cephalothorax and the abdomen.
Finally, we get to the order Araneae, which consists of 40,000+ species of spider. One feature that distinguishes spiders from other arachnids is their thin “waist” where the abdomen meets the cephalothorax (see my previous post on Daddy Long Legs for an example of this). Another is the presence of spinnerets, and thus the ability to produce silk (though not all spiders spin webs). In addition, like I’ve explained before, most spiders produce venom, with the exception of one or two families.
Well, there you have it folks. While there are other obvious and not-so obvious differences between all of these different organisms, it’s sometimes helpful to know the defining feature of a group. Now you can all sleep better at night, I’m sure…
As I said in my earlier post on misconceptions concerning spider bites, not all spiders contain venom, and Philoponella oweni belongs to one such family of spiders, the Uloboridae. This family of 266 known species (World Spider Catalog) is made up of cribellate (read: spiders with an organ, the cribellum, that occurs between the spinnerets to “comb” through silk as it is produced) orb weavers that are distributed across the globe. Individuals in this family use their finely-combed silk to wrap and strangle prey, as opposed to killing prey with venom, as most spiders do.
Sociality in spiders is incredibly intriguing, given that spiders are often known for being aggressive, solitary creatures. Thus, spiders that deviate from this lonely lifestyle are of interest to researchers like myself that want to understand the evolution of social behavior. Philoponella oweni caught my interest during my early research into sociality in spiders, when I found a few older papers by Deborah Smith that detail this intriguing species’ life history. This orb-weaver is found in the Southwestern United States, and is facultatively-communal, meaning that at times individual females will build nests alone, but at other times, they will connect their nests to those of other females. What causes this difference in behavior? An absence of web attachment sites (e.g. rocks) causes females to attach their webs to the same sites as other females. Though prey-capture and brood care (behaviors found in some spiders with higher levels of sociality) in the communal webs are carried out individually, the females will sit with their egg-sacs in a communal retreat until their young emerge.
So what could this species tell us about social evolution in spiders? What I would propose is that perhaps, when habitats are crowded or scarce, tolerance of others in or near a nest is favorable for this species. What do you think?
One of the less offensive but still widespread myths about spiders is that they all have eight eyes. While this is true for many species, and is something that can be used to distinguish a spider from other arthropods, it is not true for all spiders. In fact, spiders can have zero, two, four, six, or eight eyes, and the variety of patterns in eye placement is huge across the Araneae order!
While you’re unlikely to come across spiders with no eyes or two eyes, it may appear that they are common. Most likely, though, you’re finding spiders with four, six, or eight eyes, some of which are very small and hard to see without magnification.
Check out the great websites below for pictures/drawings of the eye patterns of more common spider families: