Tangled webs: one teen discovers the harmful health effects of tobacco smoke on spiders

Science World, Sept 20, 2004 by Britt Norlander

Since the day she was born, 15-year-old Sarah Gerin has lived around the smoke from her parents' cigarettes. She often wondered if the environmental tobacco smoke (cigarette smoke breathed in by someone who isn't smoking, but is around a smoker), also known as secondhand smoke, could be harmful. So when it was time for her eighth-grade science-fair project, she decided to study the health effects of secondhand smoke.

Sarah started by scouring the Internet and library for information. "Research helps you get ideas and strengthens your experiment," she says.

SPIDER SUBJECTS

Sarah didn't want to expose herself--or any other people--to secondhand smoke. Her research revealed another possible test subject: spiders.

Sarah learned that orb weaver spiders had spun webs the same way for over 125 million years. But when scientists exposed the spiders to drugs that affect the central nervous system (brain and nerves), the spiders' webs changed dramatically. For instance. the webs had fewer radii (a web's straight strings that look like a bicycle wheel's spokes). Also, there were fewer spirals, or web circles, and they were spread farther apart. Eventually, the exposed spiders strung together jumbled silk strings that didn't even resemble a web--and definitely couldn't nab an insect for food.

Sarah decided to find out if secondhand cigarette smoke would cause similar defects in spiders' webs. She carefully planned an experiment to learn the answer. "I wasn't really sure what the results would be." Sarah says. She designed her project so well that it won a prize at the Discovery Channel Young Scientist Challenge 2003.

Sarah began by making a hypothes,s. or an educated guess, about the outcome of her research:

HYPOTHESIS

If a spiny orb weaver spider is regularly exposed to secondhand smoke, the spider will weave a distorted web. The webs will become more distorted with continued smoke exposure.

Next, Sarah was ready to design a procedure, or step-by-step plan. to test her hypothesis. A procedure should be so clear that a friend could repeat the experiment exactly as you did it. To write a top-notch procedure, Sarah followed these guidelines:

CHECKLIST

[check] WHAT MATERIALS DO YOU NEED? Make a detailed list that includes amounts and measurements.

[check] DEFINE YOUR CONTROL (standard to which you will compare your results). Sarah had the spiders weave one web before exposing them to smoke. "That's what I tested all the other webs against," she says.

[check] IDENTIFY YOUR INDEPENDENT VARIABLE, or the factor that you change during your experiment. In Sarah's case. it is the total amount of tobacco she burned near the spiders.

[check] DETERMINE YOUR DEPENDENT VARIABLE--the factor that responds to the change in the independent variable. Sarah's dependent variable is file change in file spiders' webs.

[check] KEEP ALL OTHER VARIABLES CONSTANT. The independent variable should be the only changing factor in your experiment. One of the variables kept constant in Sarah's experiment was that she fed the spiders the same amount each day.

[check] REPEAT THE EXPERIMENT. If you get similar results for a number of trials, your conclusions will be more reliable. Sarah tested two spiders.

After following this checklist, Sarah wrote a procedure with cleat" and simple steps. Here's her award winning plan:

FINAL PROCEDURE

LIST OF MATERIALS

* adult supervision

* 2 eight-gallon water-cooler jugs

* scissors

* marker

* 2 rectangular wooden frames (30 centimeters by 36 centimeters, or 12 inches by 14 inches)

* 2 rubber bands

* 2 pieces of screen (36 cm by 36 cm, or 14 in. by 14 in.)

* 2 spiny orb weaver spiders, Gasteracantha cancriformis (GAS-tuh-ra-CAN-thuh CAN-siruh-FORM-iss)

* hair spray

* white spray paint

* 14 sheets of black paper

* water sprayer

* 60 stingless wasp larvae (organisms in an early stage of development) grown in a mixture of chicken feed and soil

* cigarettes purchased by your adult supervisor

* notebook

* pencil

PLAN

1. Cut the bottoms off both eight-gallon water-cooler jugs. Place the wooden frames upright inside the jugs. Then put one spider on each of the frames. Use a rubber band to attach a screen to each jug's top opening. Label one jug "Spider A" and the other "Spider B."

2. Place the jugs, cut-side down, in a shaded area outside.

3. Care of the spiders: Keep the water jugs in one place throughout the experiment. Mist the spiders with water twice daily. Feed the spiders by placing a wasp larva on the web every day at 4:30 p.m.

4. Collect the first webs made by the spiders before exposure to smoke: Remove the frame from the jug. Leave the spider in the jug. Spray the web with hair spray to make it sticky. Then coat it with white spray paint. Lay the frame on a piece of black paper. Remove the web and press it onto the paper. Label the paper to indicate which spider built it and the number of days of smoke exposure. For example, Spider Ns first web should be labeled: "Spider A, Day 0." Return the clean frame to the jug.

5. Look at the web on the construction paper. Count each web's number of radii. Count the number of spirals and note the distances between them. Record your observations.