Spiders are fascinating creatures that have captivated humans for centuries. One of the most intriguing questions about spiders is whether they can survive without their heads. At first glance, it seems impossible – surely the head contains the brain and vital organs spiders need to function?
However, scientists have discovered that some spiders can live for weeks after decapitation. In this article, we’ll explore the biology that enables headless spiders to live on and discuss how long they can survive in this unusual state.
If you’re short on time, here’s a quick answer: Spiders can live for weeks or even months without their heads. Their decentralized nervous system and simple circulatory system allow basic motor functions to continue operating after decapitation.
Spiders Have Decentralized Nervous and Circulatory Systems
– Their nerves are distributed throughout their bodies, not just concentrated in their heads
Unlike humans, a spider’s nerves extend throughout its entire body rather than being concentrated in their heads. This decentralized nervous system means that even if a spider’s head is removed, the rest of its body can still function to some degree.
According to entomologists, this explains why some spiders can survive for weeks after decapitation until they eventually die from lack of nutrition or inability to intake food.
A spider’s legs, for example, can still move and respond to touch even without input from the brain. This is because each leg contains ganglia or clusters of nerve cells that can independently control leg muscle movements in response to stimuli.
Similarly, though severed from the central nervous system, their heart, digestive system, and silk spinning organs also continue operating due to local nerve networks.
– Multiple nerve clusters act as mini-brains to control legs and digestion
Rather than having all its neurons centralized in one brain, spiders have multiple nerve centers or ganglia dispersed throughout their bodies that each serve different functions. There are nerve clusters in the legs that control leg motions, pedipalp ganglia that control mouth feelers, and abdominal ganglia that innervate the gut, heart and reproductive organs.
So while the main nerve cluster in the cephalothorax serves as the central processing unit, these smaller nerve centers essentially act as mini-brains controlling important body regions. This decentralized layout allows basic functions like walking, eating, silk production and heartbeat to continue even if the head is damaged or removed.
– Their simple heart pumps blood through open circulatory system
Like the nervous system, a spider’s circulatory system is also decentralized and simple compared to more complex vertebrates. Rather than a high-pressure closed circuit, spiders have an open system where blood flows freely within the body cavity or hemocoel.
At the heart of this open circulatory system is a tubular heart that runs the length of the abdomen. Contracting at a rate of 30-40 beats per minute, the spider heart pumps blood into the hemocoel where it directly bathes the spider’s internal organs.
This allows oxygen and nutrients to diffuse to tissues while collecting metabolic wastes. The lack of confining blood vessels explains why spiders can survive massive fluid loss from injury.
Decapitated Spiders Can Still Move, Eat, and Spin Webs
Legs and fangs will keep working due to localized nerve clusters
Even without their heads, spiders can continue to move their legs and use their fangs to grasp prey. This is because their legs contain small clusters of nerve cells that can function independently of the spider’s central nervous system, which is located in the head region.
These localized nerve bundles allow basic motor functions to continue in the legs, kind of like mini-brains controlling each appendage.
Research has shown that decapitated black widow spiders can walk and climb surfaces for up to 100 hours after being beheaded. The fangs are also still able to envenomate prey thanks to the independent nerve cells near the tips of the fangs.
Pretty amazing that spiders’ legs have enough autonomous control to keep going after such a drastic injury!
They can process food and excrete waste
Decapitated spiders can survive days or weeks after losing their heads because their legs allow them to find food sources and process nutrients. The fangs allow the spider to externally digest and liquify its prey before ingesting the nutrients.
An article on AskEntomologists.com notes that researchers were able to feed flies to headless orb weaver spiders and observe them excrete waste for up to seven weeks. Without a mouth or head to chew and digest, the spider uses external digestion and then absorbs the nutrients through the sucking stomach in its abdomen.
Male spiders can continue mating behaviors
Male spiders have one goal after maturing – find female mates and reproduce. Even after decapitation, male spiders can carry out these instinctual mating behaviors. The pedipalps, small leg-like appendages near the mouth, contain sexual organs and are able to identify chemical signals from females.
In an experiment on wolf spiders, decapitated males continued courting behaviors like tapping and turn sequences. They even successfully mated with females, transferring sperm before their energy resources were depleted. Pretty incredible that headless spiders can get their genes passed on!
While decapitated spiders can survive for weeks, they eventually die from starvation, dehydration, or getting stuck during movement. But the localized nerve clusters allow basic behaviors to live on for some time after a radical injury.
Headless Spiders Eventually Die From Lack of Key Organs
– No brain means loss of coordination and ability to process sensory information
When a spider’s head is removed, its life span becomes severely limited. The major reason for this is that without a brain, the spider loses critical functions related to coordination, processing sensory information, and controlling vital organs.
The brain is command central for a spider, sending nerve signals that stimulate muscles to contract and relax in a coordinated manner for walking, capturing prey, spinning webs, and other tasks. It’s like a huge orchestra without its conductor – chaos ensues.
In addition, the numerous sensory organs found on a spider’s head are lost when decapitated. These include eyes for detecting light and movement, sensory hairs for sensing air currents, smelling organs for detecting pheromones, and mouthparts for tasting.
Without these, the spider essentially becomes blind, deaf, and unable to smell or taste its environment. This prevents it from responding appropriately to threats, food sources, potential mates, and other critical stimuli.
– Exposure and dessication from missing mouthparts
When a spider’s head is removed, it loses its mouthparts including fangs and other structures normally protected within the head capsule. These mouthparts are essential for capturing and ingesting food.
Without them, the headless spider will be unable to feed itself and will eventually die of starvation.
In addition, the open wound left behind when the head is lost exposes soft internal tissues to the outside environment. These tissues normally do not come in contact with air and will quickly dry out or desiccate.
This water loss hastens the spider’s demise. The mouthparts also produce silk that spiders use to construct protective retreats. Headless spiders cannot spin these shelters, leaving them exposed to predators and harsh environmental conditions.
– Unable to molt properly and repair damage
Spiders periodically undergo molting, or ecdysis, to allow for growth and replacement of damaged body parts. However, molting requires coordination of multiple body systems and structures, including production of molting fluid from the head region to loosen and shed the old exoskeleton. Without a head, spiders cannot molt successfully.
In addition, spiders are quite vulnerable while molting and will usually construct a silk retreat or hideaway for protection. They are unable to do this if they lack mouthparts to spin silk. Any damage the spider incurs after losing its head cannot be repaired since it cannot replace its worn or injured outer covering through molting.
Survival Duration Depends on Environment and Species
– House spiders live weeks without heads due to humid indoor habitat
House spiders, like the common brown house spider, can survive for weeks without their heads in the relatively humid and temperature-controlled environment of human homes (Source). They are able to do this because their simple circulatory system pumps hemolymph (a fluid analogous to blood) throughout their body via the contractions of a heart-like organ.
While most house spiders will eventually die from desiccation or an inability to feed themselves, some can live up to one month headless if there is available moisture and prey items, like bugs, continue to walk within range of their fangs (even though they can no longer visually detect them).
This ability allows house spiders to potentially heal from catastrophic injuries, or to lay eggs even while severely injured, thus passing on their genes. Truly amazing survivors!
– Wolf spiders survive months headless in cooler, moist environments
Wolf spiders demonstrate an even more incredible ability to live without heads. Kept in cool, humid laboratory containers, some wolf spiders (Lycosa species) have survived over seven months headless – continuing to react to touch and even growing new legs to replace lost ones (Source).
In the wild, these large, hardy spiders could potentially survive such injuries over winter while dormant in moist burrows. This again allows for passing on genetic material even from heavily damaged individuals.
Just imagine coming across one of these headless wonders crawling through the forest – nightmare fuel for sure!
– Tarantulas succumb within days due to their size and metabolism
In contrast to hardy wolf spiders and house spiders, large tarantulas have high metabolisms unsuited for surviving long without a head. While they can initially survive the injury, most die within days from desiccation or starvation brought on by their high respiratory demands and inability to capture new prey (Source).
So if you happen upon a headless spider in your garage and wonder if it’s “still alive”? Yes – indeed it may be! But don’t wait around too long or try it out on your pet tarantula.
Conclusion
While headless spiders can prolong life for a short time, they cannot survive indefinitely without their heads. Key sensory and regulatory functions housed in the cephalothorax are necessary for spiders to function properly and live full lifespans.
However, the incredible adaptability of spiders allows them to persist days or weeks after decapitation – much longer than most organisms could. This ability showcases the distributed, decentralized biology that enables spiders to thrive in diverse environments around the world.
