Visibly different, part 42

This is not going to be the most popular set of photos on the web this week. You have been warned.

One particular facet of spiders is how the eye pattern can be used to identify different Families, which can help pin down species, but by itself, it illustrates how much variation is visible within the arachnids, and to some degree it demonstrates the specialization of their habits and predation. While this is by no means a complete list, I have enough images to illustrate some of these differences. For instance:

eye pattern of Lycosidae
This is the pattern of the Lycosidae, which is primarily the wolf spiders, perhaps the most common Family where people can easily see the patterns – if they choose to look. This helps differentiate them from…

eye pattern of Pisauridae
… the Pisauridae, the nursery web spiders such as the fishing spiders, that may otherwise have a very similar appearance, habits, and habitats, even when the fishing spiders are mostly found near the water – I’ve found a few, like this one, far from any distinctive water source.

Both of these are ambush hunters without webs for capturing prey, as are…

eye pattern of Oxyopidae
… the Oxyopidae, or lynx spiders, showing a radically different pattern. Both of the previous species may actively chase down prey, while the lynx usually lie in wait near something that attracts their food, like flowers. But so does…

eye pattern of Thomisidae
… the Thomisidae, or crab spiders. Are you staring to see a pattern here? If so, you’re doing better than I am, because I can’t see how these different arrangements are specific to their needs. Except for…

eye pattern of Salticidae
… the Salticidae, or jumping spiders. Here, the large anterior median (front and center) eyes can easily be imagined to assist in judging the distance to their prey before they make the capturing leap. Yet, the Lycosidae and Pisauridae both run up on their prey blindingly fast, using their posterior median eyes that are only slightly larger than the others.

The smallest variation among the images that I chose for this post come from…

eye pattern of Theridiidae
… the Theridiidae, or cobweb spiders (which really do have eight eyes like the others, it’s just the outermost pair are clustered together on one little bump,) and…

eye pattern of Araneidae
… the Araneidae, or orb weavers. Orb weavers make the classic spiderweb, the wheel shape with a spiral pattern across spokes, while the cobweb spiders pretty much spin strands at random – by web design and location, at least, these two differ significantly, but their eye pattern gives no indication of this with only subtle differences. There are a handful of four- and six-eyed arachnids as well, but most are eight-eyed, yet the variations among these are radical. Why this, when so few have evolved a different number? I couldn’t tell you, but on occasion it’s helped me pin down a species.

But if you want a real difference, look no further than…

eye pattern of Opilione
… the Opiliones, or harvestmen, though most people call them daddy longlegs. Arachnids but not actually spiders, harvestmen not only have those meager two eyes on an afterthought eye-bump (there’s probably a more proper technical name for this that I’m not going to bother looking up,) but also a single-unit body plan, or at least the appearance of one because the waistline is more a suggestion than reality. And no, they do not possess the most potent venom of any arthropod, unless some individual has bought it on the black market, because they possess no venom at all – entomologists are not even sure that they’re not strictly scavengers and never hunt live prey (which, this time, the eyes would certainly support.) It is absolutely true, however, that as a whole they believe The Beatles are vastly overrated, which is why you should never step on them; this concept needs all the support it can get.

Okay, I’ll try to dredge up something cute shortly. You’re right to be cranky.

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