You’ve got to love Urban Legends. Some of them are just so ridiculous that it is hard to believe that people actually believe them. Others, however, are understandable because they are based on misinformation that could be true but simply isn’t. Take for example the lowly daddy-longlegs, or harvestman.
To begin with, this animal, while it is an arachinid, is not a spider. I know, it looks like a spider, and spiders are arachnids, but so are scorpions, and they are not spiders either. In other words, not all arachnids are spiders.
So, how is a harvestman different from a spider? Let’s consider some spider basics. What do we usually associate with spiders? Webs! Most spiders have some sort of silk-spinning apparatus, even if they don’t spin those classic webs that immediately spring to mind. Harvestmen, however, do not. They have no spinnerettes; they have no silk glands.
How about biting? Spider bites are often attributed to any small bite-like thing that appears on arms and legs while one’s been asleep (most spiders are more likely to get squished when you roll over and are therefore not likely to bite you). Then there are spiders like black widows, brown recluses, and tarantulas—all seen as highly dangerous biters (in fact, tarantulas don’t even belong in this category, but that’s fodder for another blog). I can’t tell you the number of times I’ve heard that harvestmen have the most venomous bites, but because their mouths are too small, they can’t bite people. (Sound the buzzer here.) This is Urban Legend #2.
Harvestmen do not have venom! No venom means no venomous bites. This myth is further laid to rest when one takes a good close look at the mouthparts. Harvestmen do not have fangs, hollow or otherwise. Instead, their mouths look more like grasping claws, which is what they are, and they are too small and weak to damage our tough hides. Spiders need venom to immobilize their prey; harvestmen do not (see below).
Now, I don’t know if this next one is an Urban Legend or not, but it sure sounds like it should be. If detached from the body, a harvestman’s leg will continue to twitch. This is actually true, and it is a defensive mechanism. Harvestmen, like almost all critters in the world, have to constantly be on the lookout for predators. To avoid becoming someone else’s happy meal, these arachnids have a few strategies up their proverbial sleeves, one of which is to detach a leg and then dash away. The twitching, abandoned appendage often distracts the predator long enough to allow for a safe exit.
Other defensive actions include the secretion of foul-smelling liquid from scent glands, playing dead, or even, in some species, gluing debris to their bodies to serve as camouflage.
Daddy-longlegs are actually rather beneficial animals to have around. For one thing, they help keep the world tidy. Most species are omnivores, consuming small insects and plant material, including fungi. Other species are scavengers and as such they clean up after other things have died or pooped. It may not be the food of choice for you or me, but we should be grateful that there are animals out there that like this stuff; otherwise, we’d be up to our eyeballs in, well, corpses and scat.
This brings up another difference between spiders and harvestmen. Spiders liquefy all their meals and slurp them up. Harvestmen, however, are capable of eating chunks of food. Remember those grasping claws they have for mouthparts? Thanks to these claws, they are able to exploit a whole realm of food that spiders, which are strictly predators (although one herbivorous species was recently discovered), can not.
Do you need further convincing that harvestmen are not spiders? Then take a look at the bodies of these two animals. Let’s back up for a moment and start with insects. How many body parts do insects have? Three: head, thorax and abdomen. How many body parts does a spider have? Two: cephalothorax and abdomen. How many body parts does a harvestman have? Two—but they look like one. This is because on the harvestman the joint between the cephalothorax (head) and the abdomen is so broad that the two body pieces look like a single, oval-shaped part.
If you want to get really technical, you can look at the structures these animals use for breathing. You and I have lungs. Spiders and scorpions have book lungs, rather complicated structures that involve alternating layers of air pockets and tissues filled with hemolymph, which is the equivalent of blood. Harvestmen, on the other hand, breathe through spiracles located near their legs, and the air is transported through trachea into the body for gas exchange. This system is much like that found on insects, like grasshoppers.
Most daddy-longlegs are nocturnal, and their drab coloration reflects this. Some, however, are brightly colored and decorated with striking patterns. These individuals are active during the day, and perhaps these colors serve to communicate their presence to prospective mates, or to warn predators away.
So, the next time you see a daddy-longlegs, resist the urge to squash it, or to call it a spider. Instead, take a good look at it. Watch what it does. Is it patrolling your garden for tasty morsels? What color is it? Is it out during the day or night? It’s kind of nice to get to know your neighbors, and knowing your garden neighbors is equally pleasing. And like any good neighbor, these arachnids help look after your property for you. Give them a silent thanks and let them live to see another day.