Two Quick, Easy Ways to Collect Insects for Diversity Studies

Andrew Jennings
Product Manager, Ecology, Earth Science, and AP® Life Sciences

March 2016

Field collecting can be a great way to get your students outside and exploring the world around them. It is also a way to examine the biodiversity of the ecosystem around your school. When it comes to examining biodiversity, arthropods provide a perfect study opportunity. They are amazingly diverse and found in every ecosystem on earth, including urban areas. While not always easy to identify, they are extremely easy to collect and store. If you are looking to add a field collection component to your next diversity study, try the following specimen collection techniques.

Technique: The pitfall trap

The pitfall trap is great for collecting insects that walk along the ground. All you need is some bait and a way to safely euthanize and identify the invertebrates your students collect.

Materials (per group of 2 to 3 students)

• 2 Plastic Cups (per trap)
• 1 Funnel (per trap)
• Fruit Juice, 2 to 4 oz (per trap; grape, apple, or orange work best)
• 2 Hand Lenses
• Shovel or Spade
• 1 Small Bottle of Dish Soap
• 3 Cheesecloth Squares, 4 x 4” (per trap)
• Field Guide
• Large Container (to mix fruit juice and dish soap)

Procedure

1. In the large container, mix the fruit juice with just enough dish soap to form bubbles in the mixture. The juice acts as the bait, while the soap allows the insects to break the mixture’s surface tension and sink to the bottom of the trap.
2. Make at least one trap for your group. Each trap consists of 2 plastic cups, one inside the other. The inner cup contains the bait and funnel. The outer cup allows collectors to easily remove the bait cup for specimen collection.
3. Select sampling sites. If possible, set the traps up in several different habitat types. Options include a grassy area, wooded area, desert or arid area, a spot next to a building, or any variety of microenvironments.
4. Using the spade, dig a small hole slightly larger than the cups and deep enough so that when the 2 cups are placed inside each other, the tops of the cups are slightly below ground level.
5. Place both cups inside the hole, one cup inside of the other.
6. Backfill the hole up to the edge of the top cup, making it easy for animals to enter the trap. The cups should be flush with or slightly below ground level.
7. Place about 2 cm of the bait mixture in the bottom of the top cup.
8. Insert the funnel into the top of the trap.
9. Check the trap daily. Remove the top cup and replace it with a new cup containing fresh bait mixture. Reset the funnel.
10. Observe the collected bait mixture to make sure that all the insects have been euthanized (are submerged) before straining it.
11. Strain the bait mixture through a double layer of cheesecloth and place the collected insects on a white background for identification.
12. Using a hand lens and an online or printed field guide, identify the organisms.
13. Take detailed notes about the microenvironment surrounding each trap, include information such as the amount of shade; the soil moisture; the soil composition (sand, clay, loam); and the temperature and relative humidity at ground level. Then examine how those factors correlate with species diversity or abundance.

Technique: The aspirator

Some invertebrates spend their lives living within the bark of trees or hidden in the crevices of buildings. There are not many passive ways (such as pitfall traps) for collecting these hard-to-reach invertebrates. Instead, try using an aspirator (also known as a pooter). This device allows you to use suction to pull those insects out of their holes and safely observe them.

Materials (per group of 2 to 3 students)

• Small Clear Plastic Container with Lid (such as a film canister)
• Flexible Rubber Tubing, 0.5 cm OD, 60 cm L (aquarium airline tubing works well)
• 2 Gauze Squares, 2 x 2”
• Glue
• Water, 8 oz
• 1 Small Bottle of Dish Soap
• Large Container (to mix soap and water)

Procedure

1. Cut the plastic tubing into 2 pieces. Make one piece 18” (45 cm) long and the other 6” (15 cm).
2. Punch 2 holes into the top of the plastic container just large enough to push the airline tubing through.
3. Insert the 18” piece of tubing into one hole allowing about 1” (2.5 cm) to push through into the container, leaving the rest of the tubing to move freely.
4. To prevent collectors from inhaling the insects, you will need to create a filter. Wrap one end of the 6” piece of tubing with the gauze. A double layer of gauze is sufficient. Insert the wrapped end of the tube into the second hole allowing about 1/2” (1.25 cm) to push through into the container (see Fig. 1). Do not push the gauze completely through the hole; leave a short skirt on the outside. This will keep the gauze in place during construction.
   
   
   Figure 1.

5. Using the glue, secure the tubes to the lid so that they do not slide when you handle the aspirator (see Fig. 2).
   
   
   Figure 2.

6. After the glue has dried, attach the lid to the container. You now have a working aspirator (see Fig. 3).
   
   
   Figure 3.

7. To collect insects, take the aspirator to a tree (or cracks in a building) and move the long (unfiltered) tubing up and down along the tree’s trunk while inhaling through the smaller (filtered) tubing. You should be able to hold the aspirator with one hand and use the other to move the long tubing (see Fig. 4).
   
   
   Figure 4.

8. In the large container, mix water with just enough dish soap to form bubbles. The soap allows the insects to break the water’s surface tension, euthanizing them.
9. To euthanize the collected insects, pour the soap and water mixture into the chamber that contains the insects. Wait until all of the insects have sunk to the bottom and then strain the mixture through gauze. Place the collected insects on a white background for identification.
10. Using an online or printed field guide, identify the organisms.
11. Take detailed notes about the microenvironment surrounding each sampling site, include information such as type of tree (or building); distance to nearest tree; surrounding microenvironment (urban, field, wooded, etc.); temperature; and relative humidity. Then examine how these factors effect organism presence.

After field collection

Once you have completed your field collection and identification, use Shannon’s or Simpson’s diversity index to examine the diversity of each of your sampling sites. You can compare different microenvironments between groups or calculate the metric for the class as a whole. For more activities and in-depth use of Simpson’s diversity index and other collection methods, see the resources below.

Additional resources

• Calculating Flying Insect Biodiversity Using Simpson's Diversity Index
• Carolina Investigations® for AP® Environmental Science: Exploring Biodiversity Kit (item #180604)
• Inquiries in Science®: Assessing Biodiversity Kit (item #251422)
• Soil Organism Biodiversity Kit (item #652016)
• Carolina EcoKits®: Biodiversity

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