Why Does A Spider Curl Up When It Dies?


You might consider spiders to be the most disgusting creatures ever, but there might also be a lot of fascinating facts you don’t know about them, such as their significance in the ecosystem, the reason why they flip over when they die, and whether or is your spider playing dead?

Before we start our let’s just make it clear that spiders in no way are insects they belong to another family called ” Arachnids”but as they’re widely and commonly perceived as insects and so, not writing on our favorite and coolest creatures would be such a loss.

Back to our today’s topic , so why does a spider curl up when it dies? A quick answer would be it is a symptom of an ailing spider’s decreased coordination and failing nervous system.

Why Spiders Aren’t Insects?

Spiders belongs to a group of animals called “arachnids”.  Scorpions, mites, and ticks also belong to the same family.  Arachnids are creatures with two body segments, eight legs, no wings or antennae, and are not able to chew. Many people think that spiders are insects but they are mistaken since insects have six legs and three main body parts.  Most insects have wings. So, tarantulas are not insects they are Arachnids.

Spiders vs Insects

The reason behind curling legs of a dying spider.

The most common explanation for why spiders die on their backs is something called the “position of flexion.” When a spider is dead or dying, it cannot maintain tension in its leg muscles and naturally falls into a state of relaxation. The explanation goes that in this relaxed state, the spider’s legs curl or fold up, causing it to topple over and land on its back before it expires.

Science behind curling legs of dying spider.

 In the legs of spiders, the femur-patella joint and the tibia-metatarsus joint extend by hydraulic pressure only. Spiders do not have muscles for extending the legs at these joints. Spiders control the hemolymph (their blood) pressure in the legs to extend them and walk.

However, there are muscles for contracting these joints. So when hemolymph pressure drops, there is only a force of contraction and no force of extension. The legs therefore contract and curl up.

Other Possible Reasons Behind This Phenomenon.

Is it Gravity?

The explanation has to do with gravity. The heavier mass of the dorsal side (back) of the spider’s body falls hits the pavement, leaving it upside down.

Their body build might also be the reason behind this, as spiders have their center of gravity resting high up on their backs and so when they lose control over their nervous system they topple upside down due to center of weight.

Or maybe blood pressure?

Another possible explanation involves the flow of blood—or lack thereof—in a dying spider’s body. As the spider dies, blood flow to its legs ceases, causing them to contract. Again, as the critter’s legs fold up beneath its considerably heavier body and the laws of physics take over.

An Exception : Tarantulas

Most of spiders’ legs curl up underneath their bodies as rigor mortise sets in. The spider’s muscles only pull the legs in, they need to be alive to extend them via pumping fluid into them.

For most spiders, this results in their center of gravity to raise up and the dead spider tumbles over. But there is an exception to this when it comes to being upside down during molting and they are of course TARANTULAS.

Actually, tarantulas prefer to molt on their backs, but almost always die upright. Their legs don’t seem to tuck under the same way other spiders do when they die.

If you see a tarantula on its back, it is almost certainly molting and should be left alone. Even if it is on its belly, it should be left for a bit until you are sure it’s dead, and not just molting upright (rare but it happens).

Insecticide vs Spider’s Nervous System.

One of the most amazing things about spiders is how much they can accomplish with such a small brain. The spider’s central nervous system is made up of two relatively simple ganglia, or nerve cell clusters, connected to nerves leading to the spider’s various muscles and sensory systems. 

Several things can hinder a spider’s ability to resituate itself. Ingesting pesticides and insecticides such as bug spray disrupts the spider’s neurotransmitters and shuts down its nervous system. As a side effect, most pesticides cause a spider to go into convulsions, during which it uncontrollably kicks up its legs and often gets stuck on its back.

With its nervous system compromised and its coordination declining, the spider lacks the ability to synchronize all of its legs in order to roll over onto its side and stand back up. Depending on the pesticide, a spider can die within hours or days of ingesting the poison.

Insects or spiders with compromised nervous systems likely have the most difficulty righting themselves. Many of the most popular commercial pesticides act on the nervous system, often causing targeted insects to go into convulsions. As the spiders uncontrollably kick their legs, they get stuck on their backs, unable to muster the motor skills or strength to turn over, again, leaving them with their legs pointing toward heaven as they make their final curtain call.

Other Reasons Of Curling Legs Of Spider.

Normally, if a spider is knocked onto its back, it can use its legs to rock on its sides until it rights itself. If, however, spider can’t roll back onto its abdomen because it has become too weak or because its nervous system isn’t functioning properly, it remains stuck on its back.

Because the spider can’t get nutrients or protect itself from predators or the elements when it’s immobilized in this position, it soon dies if it can’t flip back over.

An injury or a lack of food or water can also compromise a spider’s ability to right itself. Or the spider could simply be at the end of its lifespan and its strength and coordination abilities are declining.

Conclusion.

So in conclusion the reasons behind the curling legs of a dying spider are its heavier body, lack of blood circulation in legs due to malnutrition, dehydration or weakness, or might be because of the collapsing nervous system of the spider due to insecticide sprayed on it as spider loses all its motor skills.

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