Oddly enough, not all spider-like arthropods are dangerous to humans. In fact, the opiliones, also commonly known as patonas, morgaños, or reaper spiders, are a totally harmless order of arachnids.
Due to the fact that the disposition of their chelicerae, a kind of “fangs” located before the mouth that they use to grab food, end up in the shape of a pincer and not a razor like in spiders, the opiliones cannot “bite” us. In addition, they do not have any type of poisonous gland associated with them, like their dreaded relatives.
So if we come across a “spider-like” arthropod, how do we know if it is really an opilion? . It is very simple. While in spiders it is very easy to observe the separation between the prosome (the cephalothorax or, to understand us, the “head”) and the opisthosoma (the abdomen), the opilions have these two parts of the body fused and their anatomy forms a whole globose. In other words, in the body of spiders two parts are clearly distinguished, while in that of opiliones a single piece is seen. In addition, spiders can have three or four pairs of eyes, opiliones, on the other hand, only have one pair of eyes located in the upper part of the cephalothorax.
But his story does not end here. So far, more than 6,650 species of opilion have been discovered and they can be found on practically all continents, except Antarctica. Its oldest fossils were found in Scotland and are 400 million years old, something curious is that its anatomy has practically not changed since then, such as its eight spindly legs, which can measure up to 12 cm.
Some curious facts about the opiliones:
- They can breathe through their fourth pair of legs.
- They do not have silk glands and therefore cannot build fabrics.
- They are moisture lovers. They usually live in litter, crevices and caves and under rocks and tree bark.
- They use their chelicerae to clean their legs and, in the event of having to defend themselves from predators, they can release them as a distraction maneuver. Unfortunately, the lost limb never regenerates, but they can manage without it to survive.
- Up to 60 chemical compounds can be isolated from the secretions they use to defend themselves.
- They have a tendency to group together, in fact, in the highest concentration described, more than 70,000 individuals participated. This behavior is used to better maintain heat and humidity. As you can see in this video, their clusters look like human hair.
- Unlike the rest of arachnids, opilion males are endowed with a copulatory organ and practice internal fertilization.
- In some species, males use their chelicerae to offer an oral discharge to females as a nuptial gift , to woo them.
- When it comes to reproducing, they are no longer harmless and start to fight between males to gain access to females, as you can see in this video published on the channel of the journal Nature .
- Even Salvador Dalí included them in his painting Opilió pixallits al capvespre … ¡Esperanza!
