If someone tells you that spiders also fly, you will probably think that the person has gone mad. How can spiders fly without any wings? Are flying spiders for real?
Without wasting any more time-Yes! Spiders do fly. In this article, we will see how a spider flies without wings and why do they even fly? What is the need to fly?
Sailors have reported seeing spiders coming to their ships as much as 990 miles away from the coast. Biologists have confirmed that the Spiderlings can survive for approximately 25 days while traveling in the air. (See Source 4)
A spider needs to balance gravitational force on it by electric force acting on it, and then only it can fly. Your Physics equation sheet will show you the formula F=qE, which means electric force F is equal to charge on the object times the electric field it is immersed in.
Source of Electric field “E.”
Here we need to know the electric field in the earth’s atmosphere because the spider will be immersed in it while flying ( if it can ever fly!). Before we move further, we must identify how the earth gets its electric field. Free charges come from cosmic galactic rays or CGR. Thunderstorms play a significant role in charging the earth, creating a potential difference. It is close to 250,000 Volts spread over 50 km from the earth’s surface to maximum cloud height, which is vast. The free charges brought to earth by cosmic galactic rays can flow as a global atmospheric electric circuit or GEC. Earth’s surface has a negative excess negative charge. Earth’s atmosphere has a positive charge. So the electric field on earth is pointing in the downward direction. (See Source2)
How to calculate Electric field E
Electric fields can be calculated from the above data and using the equation from equation sheet deltaV=-E*dr
On an average the electric field E= V/r=250000 volt/50000m=5 v/m in downward direction.
But this is just an average. Close to the earth’s surface, where most of the charge lies, the electric field is relatively more powerful than this average value. At the earth’s surface, its value is close to a hundred V/m (See Source 3)
Charge on the spider “q.”
This value is very much needed to find the charge on the spider. Since the electric force on the spider gets balanced by its weight, we must know the electric field to calculate the electric charge. The weight of a spider can be found easily ( by measuring or searching on google).
Force balancing “qE=mg.”
Now comes the force balancing part. As we have seen, electric force equals F=qE, where q is the charge on a spider and E is the earth’s electric field.
The spider’s weight is m*g where m= mass of spider and g=9.81 m/s^2.
To balance these two, we must have qE=mg So, q=mg/E.
The sign of the charge on the spider must be negative; then, only the spider can have an upward electric force. A positive charge on the spider will create a downward electric force in the same direction as the earth’s gravitational pull downwards (weight), which won’t make the spider weightless. So spider charge must be negative only.
Assumption- mass of spider is 0.1 grams
q=mg/E= 0.1*9.81/(1000*100)= 9.81 micro coulomb.
Is it reasonable?
Yes, it is very reasonable because when we comb our hair and then try to lift the pieces of paper, we can do that easily. So a spider that has a mass of the order of paper pieces can also get enough charges to become airborne.
Why do Spiders fly?
Although we do not know yet why the spiders fly, we can trace their origin to life in general.
The most important aim for any living being is to reproduce, or else their species will disappear from the earth. To do so, they try to minimize the risk as much as possible. They try to spread their offspring to various parts of the earth (and beyond). It gives them more chance to survive in a catastrophe etc. Also, it gives them access to more food and place to stay.
You might have heard about the Siberian birds. They cross the mighty Himalayas in flocks when Siberia gets too cold. They come to the Indian peninsula, which is quite pleasant, and have plenty of food for them. The Himalayas are the highest mountains globally, and crossing them is an adventure. However, they do it to survive and reproduce. It is survival instinct at its best.
Likewise, Spiders also fly so that they do not get stuck in the same place, and they can spread their offspring to various parts of the world, giving them a better chance to survive.