It might seem impossible to estimate how many different bugs live in a nearby field—or how many types of birds live in a forest. But wildlife biologists often have to try to determine the number of different species in a given habitat. It might sound challenging but it is important. This can help us understand how healthy the habitat is. In this activity you'll get to take on the role of a wildlife biologist by examining the biodiversity of bugs and other small invertebrates (such as spiders, centipedes and roly-polies) in your neighborhood or backyard using a homemade bug vacuum!
Ecology is the study of living things and the habitats they inhabit. In ecology the more different species that live in a given habitat, the healthier it is considered to be. The degree of species variety found in a habitat is referred to as its biodiversity. In a given habitat, the plants and animals normally rely on one another—for their entire life cycles. For example, let's say berries from a bush are eaten by a field mouse, then the mouse helps transport the seeds inside the berries to different locations, thereby allowing more berry bushes to grow. The mouse might then be eaten by a bird of prey, like a hawk, and on and on the chain goes. This web of relationships is called an ecosystem. The greater the biodiversity, the larger the ecosystem, and the healthier the habitat is thought to be.
Wildlife biologists study and monitor the health of habitats and ecosystems. One way they do this is to survey (identify and count) populations of plants and animals to determine how much biodiversity is in a habitat. In this activity you'll do your own local biodiversity survey by making a “bug vacuum” to collect as many species of bugs that you can find.
• Plastic container with lid, approximately one-cup or one-half-pint size
• Single-hole punch or leather awl (Use caution and adult help with sharp objects.)
• Two flexible drinking straws (Wider ones are better as they will allow larger bugs to be caught.)
• Pen or pencil
• Nylon stocking that can be cut up
• Clear plastic wrap
• Access to an area in your yard, a field or other outdoor place where you think bugs might live. Tip: These types of small invertebrates can often be found under rotting wood, stones and decaying leaves. And if it is hot and dry outside, more bugs may be found in shady and/or moist areas.
• With the help of an adult make a hole in the side of the plastic container (using a single-hole punch or carefully using a leather awl). The hole should be about one half inch below the top rim of the container. Make sure that when the container has its lid on, it does not block the hole.
• Using the same technique, make a hole opposite the first one, again about one half inch below the container's top rim.
• Insert the mouth end of a flexible straw into one of the holes. Stick the straw about an inch into the container. If the straw does not fit tightly into the hole, wrap tape around the straw to make it fatter until it fits snugly into the hole. If the straw is too large for the hole, gently push a pen or pencil through the hole to widen it until the straw just fits. Make sure the connection between the straw and the hole is snug. Why do you think this is important?
• Cover the mouth end of the second straw with a small piece of nylon stocking. Why do you think it's important to cover one straw like this? Use tape to secure the stocking piece to the straw. If necessary, overlap two layers of the stocking so that air can pass through but bugs can't.
• Insert the covered end of the second straw into the second hole in the plastic container. Again, make sure the fit is snug, and stick the straw about an inch into the container.
• Cut out the center of the plastic container's lid. You can do this by folding the lid in half and cutting out the center so that only a one-half-inch border around the lid's rim remains. This will be the observation window of your bug vacuum.
• Stretch a piece of clear plastic wrap over the top of the plastic container. Then snap the container's cut-out lid back on to hold the plastic wrap in place. Make sure there are no holes in the plastic wrap or your subjects could escape!
• Bring your bug vacuum out to an area in your yard, a field or other outdoor place where you think bugs might live. What types of bugs do you think you'll find here?
• If you want, you can use sticks and/or rocks to mark off a small area that is roughly four feet by four feet. This will help you define the area you are surveying for bug biodiversity.
• Carefully search a small area for bugs (such as the one you may have marked off). You will need to have a search pattern so that you do not crush the resident bugs before you suck them up, and also so you know what parts you have checked already. (For example, you could start at one corner of your area and walk along its edge, looking into the area you're surveying, and then carefully check the area inside, only walking on places you've already collected bugs from. Alternatively, you could break your area up into smaller sections and check each one at a time.) Do you see many bugs?
• When you find a bug, take your bug vacuum and gently place the filterless straw so that the end is very close to the bug. Place the other straw with the nylon filter in your mouth and breathe in forcefully. This will, like a household vacuum, suck in the bug. Repeat this process until the bug has been transferred into the plastic container chamber.
• Repeat this process until most of the bugs in your small surveying area have been collected. Tip: Don't forget to check for bugs under wood, rocks and leaves—but get ready for them to quickly scatter!
• Examine the bugs you collected by looking at them through the plastic wrap window of the bug vacuum. How many different types of bugs did you collect? How many of each type did you collect? Can you identify the different types of bugs you caught? Based on your data, do you think there is a lot of biodiversity in the area you chose to survey?
• Extra: Research which species of bugs live in your area, then repeat this activity using bug guidebooks and Web sites to identify the samples you collected. Did the kinds of bugs you expected to find in your backyard match your results?
• Extra: Compare two or more different habitats, such as a field and a forest. Do different locations have different bugs? Which habitat has more bug biodiversity? Why do you think this is?
• Extra: Try changing the conditions in your survey area, such as by sprinkling the ground with water before doing your survey or waiting until just after it has lightly rained. Does changing conditions like this affect the biodiversity you find?