Bats in the Web of Life
To celebrate the theme of Cave Week 2012, “Bats in the Web of Life,” members of the Virginia Cave Board have developed the following lesson plan for use by educators and their students. This activity is age appropriate for all groups because its content can be adjusted relative to the intellectual abilities of the participants and can be taken to whatever level desired. It results in open-ended discussions of bats’ interconnections within the natural world.
The activity was adapted from “Food Web Tangle” from Callaway Gardens, Pine Mountain, GA.
SOLs: 3.5, 3.6, 3.10, 4.5, LS 5, LS 6, LS 8
Objective: To understand the relationships between living organisms in bat habitats.
A large ball of yarn for each group of 10–12 students
Plastic name tag pockets, one per student
Food web component name tag insert cards, one per student
Markers, pencils, paper
Food Web component name tag insert cards for aboveground habitats:
1. Insect-eating Bat
8. Wild Berry
Food Web component name tag insert cards for underground habitats:
1. Insect-eating Bat [leaves guano]
2. Wood rat
3. Amphipod (shrimp cousin)*
9. Crickets (and eggs)
13. Black Rat Snake
14. Isopod (Pillbug)*
*Please note that both sighted and blind species of these animals exist in U.S. caves. Virginia does not have blind versions of cave crayfish, fish, or salamanders
Number of Participants: 10–30
The optimal size of each group is 10–12 student participants. A typical classroom would include two groups participating in the activity simultaneously, preferably one from each habitat (aboveground or underground); after completing a round of the activity, the groups can repeat the activity for the other habitat.
Before the activity:
Assign each student a character (food web component) from the lists above (bat, isopod, rat, etc).
Have each student do preliminary research on his/her living thing’s interactions with the other food web components listed above (that is, what his/her character eats or what eats his/her character, and what makes up the different parts of their character’s life cycle if they have one. See Web-based or book-based resources below.)
Write each name of the food web component/character on a name badge insert; place each insert in a plastic badge sleeve
To begin the activity:
Have each student put on the name badge for the living thing assigned to him/her so that everyone can see it when facing the student.
Have all students stand in a circle facing each other, standing about an arm’s length apart.
Use the following opening dialog for the activity:
Solicit: What do you think of when you say the word ’web’? (Answers are likely to go immediately to “World Wide Web.”)
Solicit: Are there any other kinds of webs? For example, have you ever walked into a spider web? Why did you? (Directed answer: you couldn’t see it, but it was there)
Say: Everything in the natural world has connections that you cannot see. So to ‘see’ them we’re going to use a ball of yarn in this activity.
Give one person in the circle a ball of yarn. The person holds onto the end of the yarn and gently tosses/hands the ball of yarn to another person who represents something it eats, drinks, or is eaten by. In the process of moving the ball of yarn to another person, the student should say what they think or know their connection is to the other person’s component. Students need to also think about all the life stages of their creature, for example, crickets produce eggs that may be food for other animals.
The activity continues by players holding on to part of the yarn and then moving the ball of yarn to the other players until a food web is formed and everyone is connected with yarn. It is OK if someone holds more than one portion of yarn, since most creatures eat more than one thing and have more than one predator.
When all characters are linked in as many ways as they can imagine, at least once or even two or more times, have the group vote on the least important food web component. Allow it to fall out of the circle, tugging its yarn in place before it drops it. Have students raise their hands if they felt a tug [tally up how many felt the tug]. Have students tighten up on their portion of yarn to take up the slack if possible. Ask: Can whatever needed this living thing instead use something else that is still within the web? Allow anyone with no other connection to also drop out of the circle.
Now have the group vote again on the least important food web component remaining and allow it to fall out of the circle, tugging its yarn in place before it drops out. Repeat the tally of tugs and the consequences of it as above.
Repeat this process until only a few food web components are left in the circle and there is nothing the components can eat (it breaks apart). Discuss the likelihood of their remaining components’ survival without the others.
Repeat the process for both webs.
Discussion questions: Which of the creatures had lots of connections? Which was the most important in each web? What happened when the bat was eliminated from the aboveground web? What happened when the bat was eliminated from the underground web?
End the activity with: Now you have seen the otherwise invisible connections between bats and other parts of the natural world.
1. Keep a tally of connections on the board to see which food component has the most connections in each web. Compare the most and least important food web components by ranking a list of 1 to 15 in order of importance. Discuss: “What if humans eliminated one of these components?”
2. Run the activity again with both groups forming linked circles [like a figure 8 across the room] with the two bat participants back to back in the center of the 8. Reform the two webs. Explain how some bats depend on both habitats [see background information below]. Tally how many connections the two bats have in total between the two webs. Each web now votes on the least important component, which drops out as before. Record the tugs either bat receives. Continue voting and dropping the least important component as before. Solicit: Which web falls apart first? At what point does either bat drop out? Can the bat stay alive if only one web is working? Can both webs stay together if bats disappear? Direct answers to the positive contributions of Virginia bats to cave life and as controllers of nighttime insect populations, both for human comfort and for crop viability.
3. Change the bat to a fruit- or nectar-feeding bat as part of a tropical habitat web and run the activity again. Remind students that bats in other parts of the world pollinate plants, disperse seeds, and eat other animals besides insects.
4. Discuss how humans can affect either web. Solicit: What components of each web do human beings value? Which do humans consider pests to get rid of? Teachers can run the game again and then become the human interaction in the web by standing in the center of any web as it is formed and then direct who leaves, and ask who gets tugged [Example: humans spray the aboveground habitat to eliminate mosquitoes. This kills ANY insect. All insects leave the web.]. Solicit: What happens to the web when insects are eliminated?] If humans polluted the only water source in a cave, what would happen? A dramatic way to illustrate this for the teacher to stand in the center of the web and tug on all the strings of the water-dependent cave animals!
A study of cave life includes the plants and animals found in a cave and a study of the environment in which they live. Habitats are areas that provide the food, water, shelter, and space animals need to live. Caves provide several different types of habitats. Cave habitats can be divided into categories using different methods. One method categorizes a habitat and the animals that live in it as terrestrial or aquatic.
Aquatic habitat - a water area. The animals that live in an aquatic habitat are referred to as aquatic animals. These are animals that live in the water. Examples of the aquatic animals are cave fish, amphipods, crayfish, and salamanders.
Terrestrial habitat - a land area. The animals that live in a terrestrial habitat are referred to as terrestrial animals. These are animals that live on dry land areas. Examples of the terrestrial animals are bats, crickets, and harvestmen (better known as daddy long legs).
Another division of cave habitats is by light zone.
Entrance zone - The area just inside the cave opening is called the entrance zone. This area inside the cave still receives sunlight. The light from the entrance allows some plant growth and an exchange of animals that might commonly be seen living aboveground.
Twilight zone - Farther from the entrance the light begins to diminish. This area is called the twilight zone.
Dark zone - The dark zone begins where the cave becomes completely dark and stays that way, usually throughout the rest of the cave.
Compared to surface habitats, underground habitats are food-poor. Most of the nutrients must be brought into the cave from outside.
A cave ecosystem is an especially fragile habitat that is inhabited by animals grouped together as accidentals, trogloxenes, troglophiles, and troglobites.
Accidentals (frogs, fish, newts, turtles, cows, and people) are animals that accidentally entered a cave by wandering or falling in or by being washed in during heavy rains. They can live in caves for only short periods of time because they cannot survive or reproduce underground. If they cannot leave the cave, they die and become food for other animals.
Trogloxenes (bats, bears, foxes, pack rats, snakes, raccoons, moths, swallows, vultures, groundhogs, and people) are literally “cave guests”; the word trogloxene is derived from the Greek troglo (cave) and xenos (guest). These animals visit the cave for shelter, but must return to the surface for food or to complete their life cycle.
Troglophiles (beetles, crickets, crayfish, spring fish, earthworms, millipedes, centipedes, and some salamanders) can complete their life cycles either above- or underground. These cave lovers (troglo=cave, phileo=love) survive their entire lives in dark underground places, but they can also live in a suitable dark or shaded habitat aboveground.
Troglobites (blind crayfish, blind cave fish, blind cave salamanders, blind cave millipedes, blind cave beetles, blind cave isopods, blind cave amphipods, blind cave shrimp, and blind cave spiders) are animals fully adapted to live their entire lives in caves (troglo=cave, bios=life). These “cave dwellers” cannot live aboveground. Troglobites survive and complete their life cycles in the total darkness of caves using special adaptations such as long antennae, vibration sensory organs, a good sense of smell, long fins or limbs, smaller bodies than surface species, low metabolic rates, few eggs or young, long life spans, little or no pigmentation, and small nonfunctional or no eyes in the adult stage.
Bats’ Interactions With Other Animals
There are more than 1200 kinds (species) of bats worldwide. They are the only true flying mammals in the world (so-called flying squirrels do not really fly, they glide from perches).
Bats In Aboveground Habitats
What animals eat bats? Because bats can fly and can roost in out-of-the-way places, they do not have many predators. Snakes, raccoons, opossums, and skunks prey on bats as they roost in trees or in crevasses; for this reason, bats learn to avoid small cave openings that give their predators an opportunity to snatch them while entering and exiting those caves. Owls and hawks can catch a bat in midair, a method of predation many bats use on their own prey.
What do bats eat? All bats found in Virginia feed on insects. Other bats in temperate or tropical regions eat fruit, and others feed on nectar found in flowering plants. Some species of bats are specialists, using sonar to detect ripples in water and their feet to catch small fish. Others can catch frogs or mice. Three species of bat are vampire bats which feed on blood (none are found in North America and only one in South America). These bats do not suck blood out of other mammals; the bats’ unusually sharp teeth make a small cut, usually on cattle, and then they lick up the blood oozing out of the cut.
More than two-thirds of all bat species eat at least some flying insects, which most search for through echolocation. On average each night insect-eating bats consume 25 percent of their body weight in moths, beetles, flies, cicadas, leaf hoppers and other insects. Nursing female insect-eating bats consume more than their body weight in insects each night. Studies of a colony of 150 Big Brown Bats in Indiana concluded that they consume about 1.3 million pest insects each year. One common Brown Bat can eat 3,000 mosquitoes each evening; the Pallid Bat can chase down 600 beetles and cockroaches per hour.
Bats In Underground Habitats
Some bats roost in caves, using them for sleeping during the daylight hours of warm seasons and hibernating in winter. Colonies of bats can leave a tremendous amount of guano (feces, droppings) on the cave floor. Roosting bats can therefore be the main source of organic matter entering a cave. Guano provides a food source for some lower forms of cave life, which in turn feed many cave-dwelling populations of salamanders, fish and invertebrates.
Interconnections Between Aboveground and Underground Habitats
Food webs found in aboveground habitats intersect underground habitats through animals or nutrients that enter the cave accidentally or on purpose. Trogloxenes (cave guests) may hunt, or are hunted by, animals that live entirely in aboveground habitats. Accidentals and trogloxenes that enter a cave can leave behind (in guano, their dead bodies or meal leftovers) important nutrients for other cave dwellers.
The lack of light in underground habitats means few plants can live in caves to contribute to the food web and then only near the entrance. Thus cave creatures always exist on a limited food supply, dependent on nutrients brought into the cave from the outside. This occurs by detritus [small particles of organic matter], seeds, nuts, dead leaves, and small animals being carried into the cave by flowing water, wind, gravity, or the actions of other animals. Organic matter is also carried into the cave by organisms in the form of eggs and guano (feces). Additionally insects and other animals dying inside the cave become food for other cave animals. All the organic matter is decomposed (broken down) by molds, fungi and bacteria. The nutrients then become available to microscopic animals, worms, insects, amphipods and isopods, which in turn are eaten by larger animals.
Bats actively feeding at night may leave guano sprinkled across the aboveground landscape as they fly, adding a small amount of fertilizing nitrogen to the soil.
Ecosystem Services Provided by Fruit and Seed-Eating Bats Outside of Virginia
● Fruit- and seed-eating bats pollinate about 528 plant species worldwide, many of economic or ecological importance.
● Fruit-eating bats help regenerate tropical forests by spreading seeds, some carrying them as far as oceanic islands during their seasonal migrations.
Bat-dependent tropical plants provide:
ü timber, fuel, and other wood like balsa wood
ü foods including cashew, mango, palm-hearts, acai, papaya, durian, breadfruit, fig, banana, guava, passionfruit, coffee, and star-apple
ü beverages including tequila and coffee
ü fibers including kapok [in life preservers] and panama hat straw
ü animal feed, medicines, dyes, ornamental plants, rope and other products.
What a tangled web we weave!
World Wide Web
Bat Conservation International, All About Bats: www.batcon.org/index.php/all-about-bats.html
Texas cave food: www.tpwd.state.tx.us/learning/webcasts/caves/foodweb.phtml
Australian cave food: www.kama.com.au/crc/biodiversity/cavefoodweb.html
How cave biology works: animals.howstuffworks.com/animal-facts/cave-biology3.htm
Bat Habitats and Migration: www.tpwd.state.tx.us/learning/webcasts/caves/bathabitat.phtml
Bat echolocation simulation: www.eduplace.com/kids/hmsc/activities/simulations/gr4/unita.html
Bat web: feeding: www.thewildclassroom.com/bats/feeding.html
Bat Detective: www.batdetective.com
Bat Foods: www.bats4kids.org/food2.htm
Tropical Food Chains: www.redorbit.com/news/science/1326118/bats_play_critical_role_in_the_food_chain/
Enchanted Learning: All About Bats: http://www.enchantedlearning.com/subjects/mammals/bat
Caves and Caverns, by Gail Gibbons
Caves, by Michael Ray Taylor
Caves: Mysteries Beneath Our Feet, by David L. Harrison
Let’s Explore: Caves and Caverns, A Young Explorer Activity Book, by Connie Toops
One Small Square Cave, by Donald M. Silver
Planet Earth: Underground Worlds, by Donald Dale Jackson
Published Research on Bats’ Economic Importance
“Economic Importance of Bats in Agriculture,” by Justin G. Boyles, Paul M. Cryan, Gary F. McCracken, Thomas H. Kunz, Science Volume 332, April 1, 2001, pp. 41–42. www.sciencemag.org/content/332/6025/41.short and supporting online material at www.sciencemag.org/cgi/content/full/332/6025/41/DC1.
“Ecosystem services provided by bats,” by Thomas H. Kunz, Elizabeth Braun de Torrez, Dana Bauer, Tatyana Lobova, and Theodore H. Fleming. Annals of the New York Academy of Sciences, Volume 1223, March 30, 2011, pp. 1–38. http://onlinelibrary.wiley.com/doi/10.1111/j.1749-6632.2011.06004.x/full.