Question: Are brightly colored insects found in exposed places more often than cryptically colored insects?
Background Information: Many insects are brightly colored, either because they are noxious in some way (e.g., poisonous, or sharp spines) or because they mimic something that is. Others are colored so as to minimize cues to the predator, cues that they are indeed an insect at all (“cryptic”).
How To Do It: This activity can be done in one of two ways: (a) tops versus undersides of leaves; (b) sun versus shade.
In any event, students search through accessible vegetation for all insects but ants, bees, and wasps (there are reasons). For any non hymenopteran, depending on which choice was made, the students should note whether the insect is bright or cryptic, and whether it is (a) on the top or the underside, alternatively (b) in sun or shade. After XX minutes of searching, students gather together and tally data as shown below.
Discussion: So, which is where more? Why? Ask students to explain results, thinking of the predator’s perspective and how it recognizes edible (or inedible) items. Are predators capable of learning? Note that most predators are birds. Students can handle this one quite well, I think, without additional prodding (my daughter’s kindergarten class did fine with no preparation).
| top [sun] | bottom [shade]
bright | # | #
cryptic | # | #
55. The Great Escape
Question: Once insects are approached by a predator, how do they escape?
Season: Spring, Fall.
Notes: This incorporates elements of activities 54, 53, and 52, but is different (and hands on) enough to be worthwhile anyway (I hope).
Needed: Paper, pencil, and clipboard.
Background Information: The idea is to sneak up on any insect to discover its defense reaction. For example, grasshoppers jump; many beetles fall from vegetation (they’re slow to start up flight), as do many bugs* (but some of the latter are quick to fly); butterflies and skippers dash or saunter away; many ants ignore the predator, while others run around like chickens with their heads cut off; etc.
How To Do It: Students sneak up on any insect (again, no bees and wasps, but ants okay), and: (a) note how close they get before the insect escapes; (b) note what kind of escape ensues.
Discussion: Which do you think would be easiest to catch? Do those that would be easy to catch have other means of predator avoidance? Do those that are the most sensitive to student’s approach seem to be especially large and/or tasty? Are the insects using vision, olfactory cues, or hearing? Etc. etc.
“ Bugs” in this case refers to both homopterans and hemipterans, which together used to be known as heteropterans, a nice category for ecologists.
56. The Angry Mob
Question: How do birds respond to a vertebrate predator, and who takes the lead in responding?
Needed: This requires a bird feeder outside the classroom, a feeder to which birds have been coming for some time.
Predators: The very best would be a good snake mimic, preferably (but not necessarily) coiled. Most K Mart type places (even Albertson’s) stock cheap rubber snakes that would be ideal. Also great would be a stuffed, rubber, or plastic owl, life size. Try different animals that students bring in: stuffed cats, racoons, weasels, dinosaurs, etc. Try plastic alligators.
Background Information: The idea is to set out a fake “predator” right next to the feeder and then watch the birds’ response, noting who does what. Most likely birds will demonstrate mobbing behavior, particularly to the snake.
How To Do It: At an established bird feeder, discreetly assemble students around it so they can observe bird behavior. Set out one of the fake predators described above. Observe the results. Different “predators” could be used on different days, to see how or if the birds’ response differs. Anyway, you get the idea.
Discussion: Ask students to discuss the function (if any) of mobbing behavior. Why not just ignore the predator? Or leave the area, quietly? Why scream at the predator, drawing its attention? Why join in an ongoing mob scene? Might mobbing initially arise from parent birds warning their young about the presence of a predator, and trying to distract the predator from the young? How would you test this?
57. Going With the Flow
Question: Do any, some, or all kinds of local seeds float, and why might that be interesting?
Season: Fall, Winter.
Framework: I-4-D (I-3-B-i).
Needed: Fruiting plants on campus. Envelopes or notebook, inkpen, and tape for keeping track of seed identity. A big bowl. An area of firmly-packed bare sand. A big bucket of water, or better, a hose that extends to the aforementioned patch of bare sand. A natural area of dry litter (look for a place with lots of weeds of various species, and relatively few dead leaves).
This works by far the best in sandhill vegetation, where there are few leaves on the ground and where many herbs have floating seeds, but it should work to some extent in the weedy edge vegetation of campuses and backyards.
Background Information: Note that during our heaviest rains, even the porous sands (especially those over the clays of the Hawthorne formation) saturate to the extent that some water actually flows over the surface.
Seeds of many plants may be moved short or great distances in surface runoff just over the ground surface; of course, any seeds carried into watercourses have the potential to travel tremendous distances (down the Suwannee to the Gulf and thence to South America or Portugal???). In fact, dispersal by water is responsible not only for a large part of plant biogeography on a worldwide scale, it is probably also responsible for the distribution of a lot of local plant populations, and for their ability to colonize new habitats. Probably many seeds are dispersed much farther by “sheet flow” over the ground’s surface than they are by their “biological” dispersal mechanisms.
How To Do It: Students run around collecting mature seeds of any species they can get their hands on (keeping track of which is which), directly from plants. The seeds are mixed together in a bowl, then half of the mixture is tossed on some quite firmly packed bare sand (available on most campuses and backyards). A bucket of water is then tossed at the seed pile from the side (better: a hose is brought to the pile and turned on full blast).
Which seeds are carried the farthest? How far are they carried? Do any simply sink and not travel at all (probably true for acorns etc.)? With the other half of the mixture, simply fill the bowl with water and note which seeds float on the surface; write this down. Leave overnight, and the next day, see if the distribution is the same or if some have sunk.
Meanwhile, to finish off the activity, take the full bucket of water or a hose to a natural area of dry litter. Dump the bucket or turn on the water, and see what seeds show up.
Discussion: Do any, some, or all kinds of local seeds float? In your simulated rainstorm, which seeds were carried the farthest? How far were they carried? Do any simply sink and not travel at all (probably true for acorns etc.)? After leaving them overnight, were they still floating, or did some sink? When you flushed out the weedy patch, which seeds appeared? What consequences might this type of water-assisted movement have on the dispersal of seeds on campus? Along streamcourses or in floodplains? Between continents?
58. The Hungry Caterpillar
Season: Late Spring (April June), Fall.
Framework: II-5-E (II-5-F).
Needed: Plastic freezer bags (not ziplock), clotheslines, and clothespins (alternatively, lots of jars or plastic shoeboxes); lettuce and/or collard greens, and caterpillars.
How To Do It: Students search for large caterpillars (look especially on leaves of wild grape (Vitis), Virginia creeper (Parthenocissus quinquefolia), peppervine (Ampelopsis arborea), Rhododendron, Ludwigia, Sassafras albidum, camphor (Cinnamomum camphora), parsley or other carrot relative (e.g. Ptilimnium capillaceum), bay (Persea), oak (Quercus), Citrus, etc.).
Place the caterpillar in a plastic bag, along with the following:
(1) Two fresh, unmunched leaves of its food plant (most likely the plant it was sitting on);
(2) two pieces of lettuce leaf of the same size as the host plant leaves;
(3) two pieces of collard greens of the same size; and
(4) two leaves from each of at least three naturally occurring plants that seem similar to the caterpillar’s host plant (for example, a grape vine caterpillar would be given Virginia creeper as an alternative).
Each caterpillar gets a separate jar or plastic bag. Plastic bags can be hung on string or clothesline strung across the classroom, in true field entomologist style. Make sure that each plastic bag is filled with air; a collapsed bag may mean a dead caterpillar. Also, make surhem! And different caterpillars might be specialized to deal with particular chemicals! Now, though, what plants are most likely to have the most similar chemicals? Those that are closely related, right? So, if you find a caterpillar eating one kind of grape leaf, might it not be able to eat another kind of grape leaf? What about Virginia creeper, a relative of grape? Etc. etc.
Let students observe and draw their own conclusions, but ask them to come up with tests for each of their hypotheses.
59. Advice From a Caterpillar
Question: What traits of vegetation encourage or discourage feeding by caterpillars?
Season: Spring, Fall (depends entirely on the situation).
Framework: II-5-E (II-5-F).
Needed: A fairly common caterpillar species. Plastic freezer bags (not ziplock), clotheslines, and clothespins (alternatively, lots of jars or plastic shoeboxes); collard or spinach greens, a paintbrush.
Notes: This should be an “opportunistic” activity, to be used whenever there is one kind of fairly large (i.e., late instar) caterpillar of which several individuals can be found easily.
How To Do It: Use the jar or plastic bag technique described above. Give caterpillars choices between two categories of leaves at a time, all from the natural food plant species. The choices are:
(a) Young vs. mature (but not old) leaves.
(b) Leaves painted with juice squeezed from collard greens or spinach greens vs. control leaves (same age).
Discussion: In which case is there likely to be a true difference between the two alternatives, in food quality? What is the food quality difference between old and new leaves? Which is likely to be tougher? Which is likely to have more poisonous chemicals built up? Which is likely to be drier, to have less water per amount of tissue? How might all these differences affect the caterpillar? How could you separate them experimentally, and what tests would you design? Why should caterpillars choose young leaves, then? Now, does squeezing collard juice on leaves really change their quality? Is it likely to be poisonous? If students find out that control leaves are selected in (b), then how do you explain the choice by caterpillars? How might caterpillars recognize the “right” leaves in the wild? By olfactory cues? Etc. etc. This could be developed into an activity in its own right.
60. Leaf Squiggles
Question: How many kinds of leaf miners can you find, and what kinds of plants do they occur on?
Season: All year (old mines never die, they just fade away).
Needed: Handlenses, prizes, and for the extension, paper, pencil, clipboard, and maybe a compass.
Background Information: Leaf mines can be distinguished from the rasps of beetles etc. because they are actually in-between the upper and lower epidermis of the leaf, in the spongy mesophyll in-between; the epidermis is broken only where the leaf miner (or its parasite) has emerged.
Search through weedy, shrubby, viney, and tree y vegetation for leaf miners, recognized by little squiggles, tunnels, and hollow spots in leaves.
Good species for mines: Hickories (Carya), oaks (Quercus), Lantana, sweetbriar (Smilax), Spanish needle (Bidens), cultivated squash plants, and many, many others.
How To Do It: First, send students out looking for leaf mines; the first student to find a decent one (a squiggle is best), everyone gather around and look.
Does it change in size? If so, what do you think is happening? The leaf miner is growing, dummy! see, here’s where it started, where the mommy laid an egg and the egg hatched and the tiny larva started chewing. Is the leaf miner still there, or is there a big hole at the end? How can you tell if the leaf miner has been parasitized?
Anyway, after scrutinizing one good leaf mine, students go out and try to find as many different kinds as possible. Winner gets a prize (nothing big, just a miner prize).
Discussion: Compare different leaf mines. Do the squiggly ones all go clockwise, or counterclockwise? Are there different kinds of mine in a single kind of plant? Does the same exact mine shape occur in different kinds of plants? Note that we are assuming that mine shape indicates miner species; in the very rough sense, this is okay.
Extension: If there is a desire to make this activity more “quantitative,” it could be changed: Do oak leaf miners prefer one compass direction over another (i.e., are there more on some aspects of oak trees than others?), or not? If so, what might be the reason? Etc. etc. Of course, teacher must make survey for leaf miners first (this will take the teacher all of 20 minutes), as they are not as sure a thing as most of the other animals involved in our activities.
Question: Do caterpillars naturally prefer young or old leaves?
Season: Spring, Fall.
Notes: This is a complement to #59.
Needed: Clipboards, pencil, paper.
How To Do It: Do the usual caterpillar search in the field. For each caterpillar found simply note whether it is on a young, new leaf or a mature leaf.
Discussion: Is there likely to be a true difference between the young and old leaves in food quality? What might this difference be? Which is likely to be tougher? Which is likely to have more poisonous chemicals built up? Which is likely to be drier, to have less water per amount of tissue? Which is likely to be more nutritious? How might all these differences affect the caterpillar? How could you separate them experimentally, and what tests would you design? Why should caterpillars choose young leaves, then? If students find out that the old leaves are selected more often, how do you explain this choice by caterpillars? How might caterpillars recognize the “right” leaves in the wild? By olfactory cues? Taste or touch? Etc. etc.
62. Leaf Miner Mothers
Question: Do mommy leaf miners choose larger leaves for their babies?
Season: All year.
Needed: Ruler marked off in millimeters. A plant with a fair density of leaf miners (at least 20 30 mines will be necessary, in total, for this activity).
Background Information: Again, the teacher must have made a leaf mine survey prior. Good candidates are hickories (Carya), oaks (Quercus), Lantana, sweetbriar (Smilax), Spanish needle (Bidens), cultivated squash plants, and many, many others.
How To Do It: Every time a leaf mine is found, measure the lengths or the breadths (whichever varies more) of all the unmined leaves on the same branch or stem (up to 20 leaves maximum). Then measure the length (or breadth) of the mined leaf (or leaves). At the end, compare data.
Discussion: Are leaf mines in the branch’s larger leaves, or do they seem to be in any ol’ leaf? Explain whichever result is found. Why might leaf miners thrive better in larger leaves? How can they choose? They can’t, but their mommies can. How on earth can the tiny moth, fly, or wasp mommy figure out which leaf is biggest? This question can be dealt with either way depending on the results—if there was no size selection, then the answer might be, she can’t, but if there was apparent size selection, then students can ponder away. How might you test this? Ask students to devise a “choice test” for leaf miners.
Question: What kinds of evidence do you find for the use of pine bark by animals in the past?
Season: All year.
Needed: Pine trees (Pinus elliottii, Pinus palustris, Pinus taeda, etc.) slash or longleaf are the best, loblolly is okay, but somewhat difficult to use).
Notes: This is somewhat like #3 but much more specialized.
Background Information: The point of the activity is for students to examine pine bark as an unusual “fodder” for some insects, to examine the ways in which they use it, and to discover the benefits and perils of the bark existence.
How To Do It: Students examine pine bark extremely closely and peel it apart, looking at “animal leavings” and interpreting these.
Discussion: What made the tiny perfectly round holes? Can you find any evidence? What makes the squiggly tunnels between layers of bark? Can you find any? What on earth could these things be doing with the bark? Try tasting some (it isn’t poisonous). Yuck! It tastes terrible and has a terrible texture (sort of like a doctor’s tongue depressor). How can animals (usually beetles) chew on sawdust, anyway? Why aren’t they out somewhere eating nice juicy leaves? Well, at least this is a nice protected microhabitat, isn’t it? But nothing’s perfect. What makes the large rough edged holes (woodpeckers)? Etc. etc.
64. The Old Pine Inn
Question: What animals use different parts of pine trees for food? How, and why?
Season: Spring, Fall (Winter).
Notes: Again, this is somewhat similar to #3, but with a more specific orientation.
How To Do It: Students examine all parts of a pine tree and look for animal munchers. Parts to examine: bark, live needles, dead needles, growing tips, buds, flowers, branches, trunk, bark, roots, cones, pollen.
Discussion: What traits do animals using different parts of the pine tree have? Why doesn’t a single kind of animal use all of the different parts of a pine tree? How many kinds of herbivores does a pine tree face? Are all the munchers independent of one another, or might an herbivore eating one part (e.g., the roots) possibly affect the resources available to others?
65. Fodder Fights Back
Question: What traits of plants might serve to deter munching?
Season: Spring, Fall.
Background Information: Here’s all that soft juicy plant tissue out here. Here are those hordes of hungry munchers. Do munchers have free rein, or is some of the plant tissue protected from some or most munchers?
Munchers come in at least two varieties: big (e.g., large mammals) and little (e.g., many insects). Different traits might deter different munchers.
Some plants will have no obvious traits. But here are some possibilities:
Spines and thorns. Would these be useful against large or against small munchers? And look along the edges of the leaves. Don’t some, like holly, have spines? Might these deter caterpillars that normally start munching at the edge?
Grass blades—why do they feel rough? Look at them with a magnifying glass. They have tiny silica fragments that abrade the munching apparatus of many munchers, and even wear down the teeth of cows and horses. Many other kinds of plants, such as figs (Ficus) and their relatives (Tung trees, mulberries, (Morus rubra), etc.), have crystals in the leaves (have you ever eaten fresh figs until your tongue burned?).
Trichomes—look for hairs, especially tiny sharp or hooked hairs on some species. What might these trichomes deter? (They puncture holes in soft bodied caterpillars). Also, look and feel for glandular hairs that secret droplets of sticky liquid. These might gum up ants’ legs. Really fuzzy foliage might stick in the throats of some animals. Retro-barbed trichomes on cactus, called glochids, deter large mammals.
Now, what about chemicals? Chew on an oak (Quercus) leaf or a pine needle (neither are poisonous). What happens? Does your mouth pucker up? Might the tannins responsible deter some herbivores? Don’t try to eat anything other than pine needles or oak leaves! Crush other leaves and smell. Any have sharp, aromatic smells? Might these indicate some poisons?
Gummy or resinous sap. Some plants, such as milkweeds, and many composites, including dandelions (Taraxacum officinale), have milky, gummy sap that contains latex. This glues up the mouthparts of caterpillars, grasshoppers, and many other small, generalist herbivores.
Any plants with extra floral nectaries? which enlist ants and other carnivores to rid the plant of munchers (see #s 68, 69, and 70).
Tough leaves? Might these deter some munchers?
How To Do It: Anyway, the idea is that students roam across campus, inspecting theWhat is being defended? etc etc.
66. Grasshopper Grazing