Tarantulas: Senses

Summary: The senses of the tarantula are complex and bind-blowing! Join Kiersten as she walks you through this amazing arachnid’s sense of sight, hearing, touch, taste and smell.

 

For my hearing impaired listeners, a complete transcript of this podcast follows the show notes on Podbean.

 

Show Notes:

The Tarantula Scientist by Sy Montgomery

https://study.com/academy/lesson/tarantulas-anatomy-habitat-bite.html

https://www.labroots.com/trending/plants-and-animals/18796/surprise-tarantulas-color-vision

“The evolution of coloration and opsin in tarantulas.” By Satires Foley, Vinodkumar Saranathan, and William H. Piel. Proceedings of the Royal Society B, September 2020. https://doi.org/10.1098/rspb.2020.1688

“Airborne Acoustic Perception by a Jumping Spider.” By Paul S. Shamble, Gil Menda, James R. Golden, Eyal I. Nitzany, Katherine Walden, Tsevi Beatus, Damian O. Elias, Itai Cohen, Ronald N. Miles, and Ronald R. Hoy, Current Biology, Vol. 26, Issue 21, pg 2913-2920

https://doi.org/10.1016/j.cub.2016.08.041

https://faunafacts.com/spiders/can-tarantulas-hear/

 

Transcript

(Piano music plays)

Kiersten - This is Ten Things I Like About…a ten minute, ten episode podcast about unknown or misunderstood wildlife.

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Kiersten - Welcome to Ten Things I Like About… I’m Kiersten, your host, and this is a podcast about misunderstood or unknown creatures in nature. Some we’ll find right out side our doors and some are continents away but all are fascinating. 

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This podcast will focus ten, ten minute episodes on different animals and their amazing characteristics. Please join me on this extraordinary journey, you won’t regret it.

 

This episode continues tarantulas and the second thing I like about these awesome creatures is their senses!

 

The five senses that are typically common amongst most animals are sight, hearing, touch, taste, and smell. We’re going to look at each one of these in relation to tarantulas. Buckle up listeners, this is going to be a crazy ride!

 

Okay, let’s start with vision. As mentioned in the anatomy episode, tarantulas have eight eyes. They are set just above the chelicerae. Two large eyes, that are relatively easy to see with the naked human eye, are centered in the middle of the front portion of the cephalothorax. Four eyes sit below those. These are smaller than the large eyes and sit in a line. Of these four eyes, the two in the middle will be slightly larger than the two on the ends. 

 

Now, if you’re keeping count that gives us only six eyes. The final two eyes sit on each side of the head. Once again, they will be smaller than the large front facing eyes, but they are bigger than the four eyes that are lined below the main eyes. This is typical of most tarantulas but not all species will be exactly the same. So based on the fact that they have eight eyes, their eyesight must be amazing! That’s an excellent deductive thought listeners, but in this case it is not correct.

 

Tarantulas’ eyes are capable of detecting motion and changes in light, but cannot determine visual cues in any detail. When it comes to tarantulas, more eyes does not mean better vision. But before you shed a tear for these wee animals, their eyes are perfect for how they live their lives. Most tarantulas are nocturnal, so seeing in shades of light and dark is just what they need to navigate their environment successfully.

 

It is commonly thought that tarantulas cannot see color. It makes sense that if you live in the shadows of night the ability to see color is not important, but there is some recent research that is challenging this thought. There are some tarantulas that are covered in bright blues and greens. For example, the Cobalt Blue tarantula of Myanmar and Thailand is a bright, beautiful sapphire blue. This is a truly gorgeous species of tarantula, to the human eye, but why would the tarantula produce a blue color if they themselves cannot see it? 

 

  In a research paper published in 2020, scientists analyzed the opsins in tarantula eyes. Opsins are light-sensitive proteins that are often present in animals that possess color vision. It was previously thought that these opsins would not be present in tarantulas but the scientists found some. This indicates that the tarantula can see in color, or at least some colors. We’re not one hundred percent sure why these tarantulas are blue, but the current thought is that the color is used to attract mates. Studies have not been performed with brown, red, or orange colored tarantulas so we’ll have to wait to find out if they can see in color. The closer you look at these amazing arachnids, the cooler they become. Am I right? 

 

Let’s move on to hearing. The question here is can tarantulas hear? H-E-A-R. (Laugh) Sorry bad pun. The answer is more complicated than just a yes or no, so let’s discuss the details. Tarantulas do not have ears in the traditional sense, but they are capable of hearing. 

 

As you have probably noticed tarantulas are pretty hairy. These hairs, or setae, are not just for looks, they are specialized structures that perform various functions for the tarantula. One of those functions is to detect vibrations. The setae on the legs are highly sensitive to air-borne vibrations. Quoting from a scientific paper published in Current Biology in November 2016 titled “Airborne Acoustic Perception by a Jumping Spider" these setae “are air-flow mechanoreceptors sensitive to the particle-velocity component of airborne stimuli”. Plainly said, the setae on the tarantula’s legs vibrate when sound waves hit them and this transfers information from the environment to the tarantula. I think that’s pretty cool! 

 

(As a side note, this experiment was performed with jumping spiders, which are not a type of tarantula, but the setae of both arachnids are so similar that we can make educated assumptions that this ability also applies to tarantulas.)

 

What’s even more amazing is that these setae can help the tarantula differentiate between predators and prey. According to scientific experiments, typical predators of tarantulas produce low-frequency sounds when they move. When those sounds hit the setae they vibrate at a specific rate. When the tarantula feels those vibrations they know they need to go into defense mode. Prey items produce different frequency sounds and when the setae vibrate at those rates the tarantula knows to go into hunting mode! I think it’s outstanding that these little hair-like structures can do so much!

 

Next, let’s investigate the tarantula’s sense of touch. This sense is related to the setae that covers their whole body. Essentially the tarantula’s entire body is one big sensory receptor. But it can be aided by the silk that they produce. Tarantulas that live in burrows often spin a flat web covering the ground that makes up the tunnels and chambers of their burrow. These webs help transmit vibrations to the tarantula’s sensitive legs. It tells them when a larger predator may be present or when a smaller prey item is near by. This is the same for tarantulas that live in trees, our arboreal tarantulas, it’s just not done on a burrow. 

 

These setae are so sensitive that any movement in the air can provide information to the tarantula. A slight breeze, the flap of a predatory bird wing, or a rain drop can all impart important information through the sensitive setae covering the tarantula’s body.

 

The last two senses are smell and taste. These are combined in the tarantula, or as far as we know they are (It is a bit difficult to ask them how that cockroach tastes), and once again these senses rely on the setae. The chelicerae and the pedipalps are the two anatomical structures most closely involved in taste and smell. For more information about those two anatomical structures, please listen to the first episode on anatomy. These two structures are covered in, you guessed it, setae, but these setae are different from the ones on their legs. These setae are chemoreceptors. The structure of the chemoreceptors is different from the setae used as mechanoreceptors that sense vibrations. The chemoreceptor setae are curved, double-layered, open to the environment at the end, and innervated at the base. This structure allows odors to infiltrate the setae so the tarantula can determine what they have encountered. Is it a prey item they wish to eat, a dirt clod or leaf they need to ignore, or the scent of a known predator they need to hide from? 

 

It’s been wild ride into the world of tarantula senses, and I hope you have enjoyed it as much as I have because it is the second thing like about tarantulas. 

 

If you're enjoying this podcast please recommend me to friends and family and take a moment to give me a rating on whatever platform your listening. It will help me reach more listeners and give the animals I talk about an even better chance at change. 

 

Join me next week for another thing I like about tarantulas!

 

(Piano Music plays) 

This has been an episode of Ten Things I like About with Kiersten and Company. Original music written and performed by Katherine Camp, piano extraordinaire.