Here is the dark side of the work I’m about to begin. I will have to kill some spiders. Now some people might be horrified by the idea, but I will point out that many slaughter spiders on a regular basis without a second thought. In my years as a teacher and (relatively recent) spider enthusiast, I have noticed how most people’s first reaction to a spider is to squish it without mercy. Of course, most people aren’t aware that venomous spiders are extremely rare (where I live and work, for example, there is only the black widow), and yet even when I remind them of this fact, most are unwilling to accept the importance of spiders in ecosystems. Fewer still are willing to accept that some spiders (jumping spiders, at least) can be cute.
But what is the reason that I am going to sacrifice these spiders? Only in the interest of science. Surely anybody who knows me also knows that spiders are my friends. Unfortunately, the only way to know what’s going on inside a spider is to crack them open, and I spent several hours today discussing the best possible techniques. You see, not many people have really peeked inside of spiders before. Those who have either dropped them in a preservative solution (usually one that contains formaldehyde; a foul-smelling chemical) or into liquid nitrogen so that they’d be frozen almost instantly and (possibly) easier to crack. In my personal opinion, I am in favor of dropping the spiders into liquid nitrogen, because their death will be quick and (probably) painless. The main challenge is the spider’s exoskeleton, which is easily the hardest part of a spider’s body.
So why go through all of the trouble of cracking them open in the first place? Three reasons, to be exact. First, I think that the vegetarian spider Bagheera kiplingi must have a digestive system that is different from other jumping spiders, since its diet is much more like a cow or a horse than a dog or a wolf.
If you look closely, you might notice that there are differences in the three animals, with the horse having a long and convoluted large intestine, the cow a multi-chambered stomach, and the dog nothing particularly special. This is because herbivores (plant eaters) need room for special kinds of bacteria that help the animals break down and digest vegetable matter. Since dogs primarily eat meat, they don’t need these specialized bacteria to survive.
Of course, bears are close relatives of dogs and wolves (relatively speaking), and they are nearly as vegetarian as Bagheera kiplingi. The black bear’s diet is 85% vegetarian (berries, mostly), in comparison to a 90% vegetarian diet for my favorite spider. The only way to answer whether Bagheera kiplingi is more like a lion or a lamb or a bear (or something entirely different) is to take a peek inside. This will let me know if there are any special places for bacteria inside the spider, an adaptation that has already been found in ants, and it will also help me determine what might have happened to the venom glands of Bagheera kiplingi, since it probably doesn’t need a poisonous bite to hunt down plants!