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Arthropod Investigation

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What do you know about arthropods?

Initial Exploration

Identification Activity

Designing a Study

Making and setting pitfall traps

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Making and Setting Pitfall Traps

Materials Needed

 

Exploring Local Arthropod Diversity, Part 1: Creating Pitfall Traps

 

A pitfall trap can be made from almost any cup-like container, but plastic cups that fit into each other make the most convenient traps. The first step is to dig a hole slightly deeper than the cups themselves. Then place three stacked cups into the hole. You will understand why we need three cups shortly. Fill in the area around the cups with dirt until the cups are snuggly in place. You will probably knock a lot of dirt into the top cup while doing this, but when you are finished pull out the top cup, leaving two cups in the ground. At this point you should make sure that the lip of the remaining cups is flush with ground level such that a tiny insect walking along the ground would not encounter any obstacles as they go towards the cup. This is the most important part of setting a pitfall trap. Some insects are more wary than others and if they bump into the lip of the cup or an unusual dip or bump in the ground surface, they will head off in some other direction, which would bias your pitfall trap samples to the less wary insects walking around the schoolyard.

 

After you are satisfied with the positioning of your cups you will pour a mixture of mildly soapy water and isopropyl alcohol to fill your cup about 1/3rd full. This mixture will preserve the arthropods until you return to collect the cups. The traps should be left in the ground for 72 hours, which will allow plenty of time for insects to fall into the traps. In addition, if each school uses the same length of time, we will be able to make more rigorous comparisons of arthropod diversity among schools.

 

During the 72 hours that the traps are operating you should occasionally return to your traps to make sure that they are still set properly. Animals such as birds and rodents will often take an interest in the traps and even attempt to eat insects that have fallen into the trap. If the top cup has been filled with dirt, you can remove it, empty the dirt into another container, and replace the cup with fresh mixture of water and alcohol. You should look through the emptied dirt for any arthropods that might have fallen into the trap. Remove these arthropods and place them in a container with alcohol and label the container.

 

Collecting Your Pitfall Traps

Local Arthropod Diversity, Part 2: Collecting Arthropods from Pitfall Traps

 

After 72 hours you will collect your pitfall traps. The key to collecting you traps is labeling. The content of each pitfall trap should be transferred to a separate container and clearly labeled. The label should be written in pencil on a piece of sturdy paper and placed inside the container. We use pencil because almost all ink will dissolve in alcohol, and we place the label inside the container because labels taped to the outside of containers frequently fall off or are somehow destroyed. The label should contain the following information:

 

Other information, such as the length of time the trap was operated, details about location, and if the trap had been disturbed at some point, should be recorded in your field notebook. After the content of each pitfall trap has been transferred to its own container, isopropyl alcohol should be added to each container to preserve the contents, which can be sorted at a later date.

 

Sorting the Contents of Your Pitfall Traps

In order to sort the contents of your traps you will need a large light colored dish or tray...