There are times when I regret not going to college, and finding out more about some of the things that interest me on a regular basis. But then I think about it, and realize right now I can concentrate on certain topics without having to satisfy some requirement for things I couldn’t care less about. So I guess the glass is still half unbroken, or something like that.
Anyway, say hello to a common spider crab (Libinia emarginata) that can be found in Florida waters, among many other places. [The blotch in the left foreground is a slipper snail on the aquarium glass]. They’re shy, and their pincers are tiny and good only for feeding, so they utilize defensive camouflage, but in a totally cool way. They have the ability and instinct to obtain pieces of seaweed and plant them across their upper carapace with the help of a strange texture on its surface, and in this way, they blend into their typical habitat of seaweed-covered rocks. My specimen here, caught by hand and photographed within a fish tank, also sports quite a few small anemones, those ghostly white fringes all over its back. Whether it actually planted them itself or they simply liked it as a host, I cannot say.
Unfortunately, there’s a lot I cannot say about this one, but I’m trying to locate the answers to my questions, and plan to update this post when I have them. You see, simple coloration camouflage I understand. Simple behavioral traits, like holding still, I understand. But this is something different. Here we have a species that not only has a specialized physical trait, Velcro-like hooks in spots on the chitin called setae (which may even provide a preferential surface for anemones), but a specific behavior too, one that doesn’t seem to serve a combined or translatable purpose. You see, in order to get the seaweed to stay put, the crab actually chews the ends into a fray that catches on its setae, then puts the seaweed in place. Some studies have shown that it knows what seaweeds are more repugnant to its predators and preferentially chooses them. It has also been shown that this is more prevalent with the younger, smaller crabs, and that both the surface and the behavior disappear as they get older and less threatened by predators.
Evolution can be a convoluted thing, and the processes that lead to the forms we see now aren’t always easy to determine. The process of choosing select seaweeds, preparing them with a compatible surface, and placing them on its body has the deceptive appearance of reasoning and foresight, something that is undoubtedly lacking – crab brains aren’t very complicated. This is an ingrained process that’s been selected for over a very long period, but just how do you select for it?
It’s easy with adaptive traits like color. The harder it is to see a species, the harder it is to find it and eat it, so the ones with color that more closely matches the surroundings get eaten less and reproduce more, passing on those color genes. Simple. But a behavior that also relies on a specialized physical trait is something else, one that’s hard to work backwards from (and that, so far, I have not found answered by research.) I could perhaps see that the setae might have snagged seaweed by itself while the crab moved through a mass of it, and thus the crabs that grew rougher spots on their carapaces gained a camouflage benefit from the incidental adherence of stray vegetation. So, how did it evolve a behavior to place chewed stems on its back? I could spend a lot of time speculating, and have, but it hasn’t led anywhere convincing, nor do I think my guessing is meaningful in any way. We know, through roughly 150 years and uncountable hours of research, that these kinds of things develop in small increments over long periods of time. I just find it fascinating the traits that have been produced by the process, with only a few basic rules to produce them.
As odd as this might look, most of what you see isn’t really part of the insect at all. This is the larva of a green lacewing fly. At this stage they’re predatory, meaning they eat other insects, mostly aphids. The cluster of junk on its back is molted exoskeletons of other insects – what kind, I haven’t been able to identify. Perhaps aphids, perhaps other lacewing larvae, spiders, or even preying mantis. It serves as camouflage, making a tasty insect (I’m assuming, anyway – something must find it palatable) into a dry bit of chaff. And, it serves an additional purpose, in that anything that does recognize it as food stands a much better chance of getting a mouthful of detachable skin (no Goldmember jokes now) instead of the juicy, nutritious insect.
In case you wanted a better idea of the scale, here it is again, held by the chaff between my thumb and forefinger. And yes, just so you feel better about me sacrificing The Girlfriend in the name of bug pictures, it got its own chance to gnaw on me too. Lucky for it I hadn’t found it earlier when I was looking for some insects to feed a shy lizard.
Last weekend, I flew up to central New York – a vast region often called “upstate” to differentiate it from New York City, which is what most people think of when they hear “New York.” If you’re one of those people, go look at a map, and get over it. I grew up in the Finger Lakes region, and returned there briefly for a kind-of family reunion. That was all well and good, I suppose, and I got to meet a cousin I hadn’t seen or talked to in, seriously, 37 years. But I was more motivated to get out and appreciate the area in late summer, because it’s a gorgeous area with some pleasant geography. Not being a winter person, however, I’m glad not to be there when the snows arrive…
This region of NY appears to feature fossils from the Devonian/Silurian period border, somewhere around 416 million years ago. Ocean life was abundant, but just starting to get complex, and terrestrial plants weren’t really around yet. Here I have a brachiopod, probably a spiriferidine, which shows the impression of the underside of the shell (towards the bottom of the photo), as well as the petrified remains of the shell itself (the lighter portion in the center of the pattern). The lines sloping crosswise to the “ribs” are growth lines of the organism. Don’t get the impression I know all of this offhand – I found out most of this while researching this post…
And I have this thin slab, 4 cm across at its widest point, that shows a collection of shells virtually indistinguishable from a modern day scallop – the only thing missing are the little tabs near the joint. Now, think about this a second: in 416 million years, the outward appearance (and primary function) of this organism has changed barely at all. In that same time, the first animals left the sea for the land, developed into countless species (like the dinosaurs), most of which vanished through extinctions, and we ourselves were probably some rodent or lemur-like thing when the dinosaurs died out 65 million years ago. Australopithecus afarensis, commonly referred to as “Lucy” and potentially our ancestor, comes from about 3.5 million years ago and looked only vaguely like us. But “scallops” barely changed at all. That’s what I call a successful organism. Not to mention tasty wrapped in bacon.
My favorite, from the short exploration, is this one. Splitting it open, I found two fossils overlapping. One of them certainly seems to be a plant, and from this time period, it would have to be aquatic, since land plants weren’t this fully formed. And since they rarely fossilize, I was pleased to see it. It’s draped across something that I haven’t yet identified, but I’m reminded irresistibly of chitin, the hard exoskeleton of something. It’s very thin, and actually has a hollow tunnel directly underneath it from yet another species – it appears it may have even conformed to the shape of the underlying organism. It’s also a distinctly different color from the surrounding rock. And I have both impressions, top and bottom, on the split rock layers. The whole chitiny structure is about the size of a fingernail, so the “leaves” are tiny and delicate indeed.
The truth is, even professionals working high-dollar assignments and presenting stunning images to magazines only keep twenty-five to forty percent of what they shoot, on average, and this is without resorting to the new digital technique of “try it and see what happens.” Controlling every aspect that might go into an image is next to impossible, and even if it weren’t, we probably wouldn’t be very impressed with photos that were meticulously staged. But overall, many, many photos go into the trash, and I’m no exception. My keeper rate runs 40-66%, which sounds great in comparison, but it may simply mean I’m less critical and demanding than others.
There’s this funny thing about humans – we seem to have this problem with counting above, “two.” I mean, of course we can do it, but we prefer not to. So every time we have to make a decision, we try to cut our choices down to two. And to make this easier, we tend to resort to superlatives, and try to push choices to their extremes so we don’t have to qualify our decisions any more than is necessary. By this I mean, good or evil, liberal or conservative, smart or stupid, healthy or toxic, nature photographer or lowly peon…