Science Buddies: "Ask an Expert"

Hey Science Buddies community!
My teacher wants my science fair experiment to be confirmed by a scientist before I move on. My science fair experiment is to test never before tried natural spider repellents in comparison to consumer available natural spider repellents. I will be using wasabi and bitter melon for my variables since I learned that spiders tastes with their feet. My science fair project will test the spiders' taste for spiciness and bitterness. I will be using Star Brite Spider Away as my consumer available spider repellent. The spider I will be using is the cellar spider or daddy long legs as called by some since they are readily available for me to purchase. My teacher wants for you to confirm my procedure and more specifically confirm if the amount of tests I will run is sufficient. Here is the procedure I developed (broken down into parts):

Procedures
Making the Repellents:
1.) Wasabi repellent:
Obtain the wasabi powder, water, 1 spray bottle, measuring spoons, baking soda, and 1 cup. Measure out ½ tea spoon of wasabi powder and mix it with 3 table spoons of water. Add in ¾ tea spoons of baking soda to reduce the smell of the wasabi. Strain then pour mixture into the spray bottle.
2.) Bitter Melon repellent:
Obtain the bitter melons, a cup, a blender, and a knife. Cut open the bitter melon and remove seeds. After the seeds are removed place the bitter melon and ¼ cup of water in the blender and puree until turned into juice. Strain then pour mixture into the spray bottle.
Creating the Experiment Environment:
1.) Containing the spiders:
Obtain the 24 spiders, 24 cups, a stick, and one dice. Place three rows of eight cups and label each row as control, bitter melon, and wasabi. Assign the dice faces to each row. (ex: 1,2 will mean placing the spider in the control row, 3,4 will mean placing the spider in the bitter melon control, and 5,6 will mean placing the spider in the wasabi row.) This step is to eliminate bias. If one row is full but its dice number show up, ignore it and roll again.
2.) Creating the test zones:
Obtain the cardboard pieces, duct tape, scissors, a ruler, and a pencil. Measure out 3 120 cm by 30 cm pieces of cardboard with the ruler and cut them out. Roll them into a circular wall figures and use tape to make them keep their shape.
Conducting the test:
Obtain the 3 rows of 8 spiders, the 2 variable spray bottles, the control repellent, and the 9 walls. Split up the walls into 3 rows of 3, sectioning out one row per repellent. Spray the inside of the walls with the correct repellent. Secure the sprayed wall on the ground then place one spider in the center of the inside of the wall. Observe the spider’s reactions for 10 minutes then place it back in its cup. Do the test over 8 times switching the spider each time. Repeat this for the other 2 repellents.

Thank you so much for your help!
I hope to hear from you soon!

-Justin

Hi Justin,

From your description, it seems to me that you'll be putting the spiders in the middle of a circular chamber, the walls of which are sprayed with "repellent," and observing whether it spends time adjacent to the walls or in the middle of the chamber. Is this right?

Given that the natural drive of the spiders may be to hug the walls and/or climb, this design may cause problems. If you give them a choice between "on the wall, but near the repellent," and "away from the wall, but away from repellent," your data may be complicated by the conflicting drives of the spiders to climb the wall and avoid repellent.

You might want to consider putting them in a rectangular chamber that has a sponge soaked in repellent at one end, and a sponge soaked in water at the other. Then you can measure how much time they spend in each half of the chamber. With this design, you'd get data on whether each repellent (including the commercially available one) worked to repel spiders. If you liked, you could also put your natural repellents on one side of the chamber and the commercially available one on the other side, to find out how well the natural compounds work compared to the Spider Away.

Your idea to use a dice roll to assign spiders to treatments is a good one. Randomization is an important part of experimental design. There are other aspects of the experiment that you could randomize to good effect. For example, you might imagine that one side of your experimental chamber might, for some reason you don't perceive, seem "nicer" to spiders than the other end; therefore, you might want to randomize which end of the chamber gets the repellent and which end gets the water control, for instance.

Best,

Will

Thank you very much Mr. Walker.

I have one minor question: What should I place on the two other sides of the rectangular chamber in your suggestion? Two walls will contain the sponges that are soaked in a liquid, so will the remaining two walls be left dry?

I will definitely use the randomization idea for the walls and change my chamber design.

Thanks again!

Justin

Justin,

I have another comment--there are several different organisms that are called Daddy long-legs, and only one of them is an actual spider. Thus, make sure you have this arachnid: http://en.wikipedia.org/wiki/Cellar_spider and not this one: http://en.wikipedia.org/wiki/Harvestman . You said cellar spider, so you are probably using an actual spider, but you probably want to be sure.

Good luck!

Hi Justin,

Since you basically want to give the spiders a binary choice (toward or away from the "repellent" being tested), maybe the best thing would be to use a clear narrow tube, with a sponge at each end. If the substances you're testing have a strong enough effect, I bet that would work fine.

It occurs to me that with this setup you're testing the ability of the substances to deter spiders through diffusion of a chemical repellent. Something to consider is that if the species you test doesn't have a "good sense of smell," you may not be able to detect an effect for any of the chemicals. You may want to also experiment with contact deterrence, perhaps by covering the floor of a chamber with two pieces of filter paper, one of which has been sprayed with the chemical to be tested. Then you could record the amount of time the animal spends on each of the two pieces of paper.

When you're ordering your spiders, one last thing to consider is that for your experiment to work well, you want to be sure you get a moderately active species. My guess is that harvestmen probably move around a lot more than cellar spiders, and so they might be a better choice. Not that I'm an expert on that! (Harvestmen, as MelissaB pointed out, aren't technically spiders although they look superficially similar)