How to tell if a spider is poisonous or harmless

Understanding whether a spider is poisonous or harmless to humans is not so simple. There are more than 50,000 species of spiders around the world, but just as many of them are terrifying because of their size and color, few of them are actually dangerous and poisonous for people. Most of them are actually harmless to humans, and even the most feared and dangerous spiders, such as the fiddler spider, are actually not very aggressive, as they only use their venom when cornered.

In total, there are at least 1,620 different species of spiders in our country, all listed in the national checklist developed by Paolo Pantini and Marco Isaia. Some of these species have gained a lot of media attention after accidents involving them, but even then, the number of people who have died from these spiders is very low, given that they do not have particularly lethal venoms.

However, this does not negate the usefulness of trying to distinguish poisonous and therefore dangerous species from harmless ones, so that we know how to deal with them when we encounter these animals or find them hanging in the cellar, and thus avoid accidents. However, for this we need to have an idea of ​​exactly what spiders are and know their ecology and why they produce venom.

Spider identification

Spiders belong to a specific order of arachnids, namely the order Araneae. In fact, we also equate arachnids with ticks, scorpions and opiliones, very different animals. Arenaids are known to have a distinct body in two parts: cephalothoracic, which has a mouth, feet, sense organs and chelicerae, e.g belly, where the genitals, heart, digestive tubules and many other systems are present.

Furthermore, unlike insects, which have three pairs of legs, spiders have four, bringing the number of limbs to eight. Another typical ability of spiders is to produce silk through some special glands in the abdomen that flow directly into supply chainspecialized bodies for building webs.

Most species also have very long and thin legs covered with some kind of feathers, which allows them to detect any movement on the surface of the canvas. Spiders don’t have real teeth. They inject their venom into their victim through the “fangs”, the chelicera. They produce venom not as a defense system, but to quickly capture and immobilize their prey, especially insects or other small animals.

Venomous spiders vs harmless spiders

Spiders stun or kill their prey with venom, but only 1-2% of species produce toxins capable of having significant effects on humans. Unfortunately, however, it is difficult to recognize the degree of dangerousness of a species based only on morphological and aesthetic features, since there are apparently anonymous species that are very dangerous and very showy and showy species that are, on the contrary, harmless.

In order to avoid being bitten by poisonous spiders, we must first of all have great respect for these animals and we must have an eye with which we interpret the information we have well. In fact, poisonous species have very different colors and sizes. And in order to understand whether a certain species is really dangerous, we must first know the area we are visiting well, know the main characteristics of the most common species and think about the probability of meeting a dangerous species in a given habitat.

When we do this, we also need to compare the morphology and colors of the animal in front of us with other venomous species about which we have more knowledge. For the simple fact that some venomous species do not have unique characteristics, experience and the ability to carefully interpret the attitudes of any spider is very important.

I’m going to compare one Mediterranean black widow with fiddler spider on the other hand, it can be noted that there is not much in common between the two species, except of course that they are spiders. In fact, these species come in very different sizes and colors, live in different contexts, and even their bites produce unique effects. Their main difference from species that are harmless to humans is that they have chelicerae and stronger, larger venomous teeth. However, in Italy it is enough to know the morphology of these two species to feel relatively safe, given that these are the two species of spiders considered the most dangerous to humans.

With most other spiders, they can cause small abrasions around the bite opening, but these wounds are not very dangerous unless we are particularly sensitive to their venom. However, in this case, even a bite by an ordinary spider – in very rare cases – can have more serious consequences and require medical intervention.

Distinctive signs of poisonous spiders

However, due to the small number of poisonous species present in our country, we cannot fail to mention some basic characteristics that are essential for recognizing the two most dangerous Italian species in nature. Either Mediterranean black widow or malmignatta (Latrodectus tredecimguttatus) that the fiddler spider (Loxosceles rufescens) actually have larger chelicerae than other spiders and present distinctive alarm signals and colors.

Coloring and marking

Violin spider

Some species of venomous spiders use their coloration and specific patterns to signal their danger to other animals. This is even more true for those species that are more exposed to predation, live in very open contexts, or are predator-rich. Thus, the red spots of black widows warn their predators – including many birds – that they are extremely poisonous before they clumsily try to catch them.

However, when we look at the violin spider or any other species considered poisonous, we realize that this rule does not apply to everyone. The spider actually has a violin anonymous brown pigmentationI respect many other animals and if it wasn’t violin drawing which stretches from the head towards the belly, its surface would lack any other identifying mark.

On the other hand, some harmless species – such as grasshoppers (grasshoppers) – have “stolen” the threatening colors of brighter species and use them as a defensive element, despite being harmless. This phenomenon is defined Batesian mimicry and makes it even more difficult to quantify the danger of a species in the wild.

Size and shape

Mediterranean black widow

In general, most poisonous species scattered around the world – such as american black widow AND tunnel spider – they have highly developed fangs with which they inject larger amounts of venom. However, size is not a good measure of how dangerous an animal is. Suffice it to say that the “menacing” tarantula, which can reach tens of centimeters in size, is much less dangerous than a tarantula. digging spider which reaches a maximum of 4 cm.

This happens because, on the one hand, the danger of spider venom results from the specific evolution of each species, while our minds are predisposed to react more quickly to larger species. The size of spiders thus changes our perception of risk towards them and sometimes promotes accidents because some bites are caused by small poisonous spiders that were previously thought to be harmless.

Behavior of venomous spiders

One of the great legends about poisonous spiders is that they hide in crevices and are always ready to attack us. This is actually not true, given that not all spiders that are capable of producing venom produce it in abundance and are ambush animals. In fact, most venomous spiders, while more dangerous, they use bites as a last ditch defense and before attacking an animal or a person, they always try to break free or take refuge in a safe place.

For these species, the production of venom is extremely costly in terms of energy, and for this reason, wasting their supply would be counterproductive, given that venom is their best hunting tool to immobilize their prey, not to defend against animals that are “huge” to them. like us humans.

On the other hand, it is also true that some spiders are more unpredictable than others, a behavior that makes them more difficult to manage. For example, famous banana spider (Phoneutria nigriventer)which is considered by many scientists to be one of the most dangerous in the world, has a bad habit of taking refuge among bunches of bananas, and whenever it feels threatened, it shoots from its perch and bites the first unfortunate person that comes within range.

The Mediterranean black widow on the other hand – although less dangerous than its American “cousin” – is well known bite with a lightning fast movement, when threatened. Its bite causes sweating, nausea, vomiting, fever, headaches and, in the most serious cases, loss of consciousness and death, but it never attacks our species as a precaution. In our country, it is found in Sicily and Sardinia, as well as in Liguria, Tuscany, Lazio and a large part of southern Italy.

What to do in case of a bite?

In the event that you need to help someone who has been bitten by a spider – or in the unfortunate event that you have been bitten yourself – remember that time is of the essence in these cases. Spider venom can actually become more active and dangerous as the minutes pass, so you need to act quickly and clean the wound. If severe pain is present, ice can be placed on the bite to reduce skin sensitivity.

You should never try to extract the venom by sucking or squeezing the wound. This could actually lead to bleeding and involuntary ingestion of the poison itself. After washing the wound, this must also be done immediately call for help if the bitten subject shows even mild symptoms.

While waiting for help to arrive, the bitten person must lie down and raise the affected limb slightly if possible. If he was bitten instead on the abdomen, torso or behind, it is important not to cover him with clothing, as sweat could complicate the situation.

For black widow bite Doctors often treat seizures with benzodiazepines, mild sedatives that help relax muscles. However, the antidote is given if the symptoms are really severe and hospitalization is usually required for all victims under 16 or with other pathologies related to the cardiovascular system.

In most cases, however, spider bites do not cause serious problems, except for some local reactions caused by perforation of the skin through the chelicerae. In this case, just use ice to reduce the size of the pimple and use antihistamines if you know you are sensitive to spider bites.

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