Alternative: For students who understand graphs, you could “randomly” select plants of the given species, and measure the mean distance to the three nearest neighbors of the same species, using this as a measure of density experienced by the plant. Measure herbivory as above or some other way. Then, plot herbivory against “clumpedasy, if the campus or backyard has (as many do) (a) several oak trees of a single species (preferably either laurel oak (Quercus hemisphaerica) or live oak (Quercus virginiana), but water oak (Quercus nigra) is okay too); (b) at least one tree that is standing alone, and at least three others that are standing close to one another in a clump.
44. Acorn Weevils: Looking for a Home
Question: Do oak trees growing in clumps experience more acorn predation (by Curculio weevils) than isolated trees?
Needed: This will be a great activity, and extremely easy, if the campus or backyard has (as many do) (a) several oak trees of a single species (preferably either laurel oak (Quercus hemisphaerica) or live oak (Quercus virginiana), but water oak (Quercus nigra) is okay too); (b) at least one tree that is standing alone, and at least three others that are standing close to one another in a clump.
Season: Late Fall, Winter (November to February is best, or whenever acorns have dropped but not yet rotted).
Framework: 4C (II5D).
Notes: This is just the same as #43 above in concept, but might work much better in places with oaks.
How To Do It: Basically follow the scheme above, except that the discussion centers around seed predation rather than leaf herbivory.
Note that a seed is a packet consisting of (a) the baby plant, or plant embryo; (b) food for the sprouting plant; and © some sorts of protection, physical and often chemical.
Well, food for the sprouting plant is also food for freeloaders. Although
tiny seeds of many plants don’t offer enough food to attract macroscopic animals (they do attract fungi, bacteria, and tiny soil arthropods), seeds of some plants are large enough to attract insects, birds, and mammals. Acorns in particular are big, starch-filled packages.
Weevils (long-snouted klutzy looking hard beetles) of certain species (in the genus Curculio) are especially fond of acorns. Females lay eggs inside an acorn long before it falls from the tree; they use their long snouts to drill through the shell of the developing nut, and lay their eggs on the nutritious tissue inside. The larva hatches, gets fat and sassy on the rich starch food inside, and finally makes its way back out just before the acorn falls, or soon thereafter. It pupates, and emerges an adult beetle. See mid-1989 National Geographic article on precisely this relationship.
Students can very easily note whether or not an acorn has been preyed upon by looking for the exit hole of the beetle, a small, perfectly round opening either on the side of the acorn or at the base.
Note: The weevil larvae are themselves parasitized by parasitic wasps—see extension below.
Half the class goes to the isolated tree(s), the other half to the clumped trees, and students simply examine acorns one at a time. Continue for the time allotted, but make sure that each group examines an equal number of acorns, e.g., 200 each (this will prevent having to compare percentages or fractions). Simply note the number of acorns without any hole and the number with a hole.
Discussion: Again, making sure that the total number of acorns examined in each situation is equal, simply ask students to compare: In which situation are more acorns weeviled? Post-data discussion is similar to that in preceding activity. Make sure that students open up several acorns, those without holes and those with. Any evidence of weevil occupation (of course there is!)? Any evidence for weevils that had been parasitized?
Extension: THREE’S A CROWD!
Look for parasitized weevils in acorns. Remnants of larvae characterize parasitism. Set up an activity similar to the weevils-in-acorns, but asking the Question: do clumped trees with clumped acorns have clumped weevils which in turn experience a higher parasitism rate than do the scarcer weevils in acorns on isolated trees?
45. Elbow Room for Nipple Galls
Question: Are hackberry galls spread evenly over leaves, or do some leaves seem to be better than others? and other galling questions.
Season: late Fall, early Winter (hackberry leaves fall mid November and will rot by late January).
Framework: I-4-C (I-2-B, II-5-E).
Needed: At least one good sized hackberry (Celtis laevigata, also called sugarberry) tree on campus. Clipboards, pencils, and paper.
This activity is best done on a dry day, because wet leaves are hard to handle. Note that crisp blackened fallen leaves are fine to use; the nipple galls can be discerned easily until the leaves actually are so rotten they fall apart at the touch.
Notes: Even if you find a tree that has one of the other psyllid species as the most common, you can use it to do this activity.
Background Information: Nipple galls are homes of one genus of plant lice (which are psyllids, relatives of aphids). Actually, there are at least five species of hackberry gall psyllids here, but the most common is one that makes a nipple like gall about 3 8 mm across, on the leaf.
Note that psyllids live off of nutrients coming through the plant’s vascular system (“veins”). Note that too many psyllids per leaf might mean fewer nutrients per psyllid (or per gall). So, make a prediction: Will there be some leaves with many galls and a lot with none, or will there be only a few psyllids per leaf?
Note, then, that this prediction makes an implicit assumption: Leaves are equally good. What if there is variation among leaves in quality? What sorts of things might vary? Size, nearness to nutrients, sun vs. shade (more nutrients in sun leaf), etc.?
How To Do It: Anyway . . . students scuffle through fallen hackberry leaves (November January—see below) and simply note the number of nipple galls [or other species] per leaf. Make a tally sheet with columns headed 0, 1, 2, 3, etc., and simply tally each leaf. Make sure that zeros are counted. For each leaf, note S, M, or L, for small, medium, large (the easiest assessment of quality).
Discussion: At the end, look at the results. Do most leaves have only a few galls? Are there any with lots more than the “usual” (modal) number? If so, anything unusual about those leaves? Is there a pile up of “S”s at the 0 1 end, and a pileup of “L”s at the high gall numbers end? DISCUSS. Ask students to speculate on how psyllids, tiny critters that they are, could even tell whether a leaf was large or small, and how many pselfish psyllids it already had on it, etc.
46. Hit the Road
Question: Do dispersal traits of plants differ with habitat, and why might this be so?
Season: Fall, Winter (Spring—some plants have set seed by late Spring).
Framework: I-4-D (I-3-B-i, I-3).
Needed: At least two different habitats on campus (easily accomplished), including mowed lawn, lawn edge, etc. Millimeter rulers. Clipboards, pencils and paper.
Background Information: See Handbook pages 13, 34-35, and 41-43.
How To Do It: Students simply range from habitat to habitat, and in each habitat, for each plant species encountered in that habitat, note the size of seed (use millimeter rulers) and the kind of dispersal mechanism: bur, exploding seed pod (e.g., Cassia, Geranium), wind dispersal, simple drop dispersal (no obvious mechanism), fleshy fruit, animal dispersed nut (e.g., oak (Quercus), hickory (Carya), etc.
Make a list for each habitat. Characterize each habitat by shade on the ground and patchiness (whether the habitat occurs as more or less continuous habitat or as patches isolated from one another).
Discussion: Just examine the different dispersal mechanisms and discuss them in terms of the habitat characteristics the students have noted.
In habitats that are shady at the ground, would a tiny seed make it? Or might a seed with more “parental care” (food resources provided, more or less, by the mother) be better suited? Is there a relation of seed size with shadiness? Now, what about distance traveled? Which travels farther, small or large seeds? Can large seeds float in the wind? Can small seeds? How far could a small seed float in the wind? Etc. Let the students come up with almost all, if not all, of the ideas. How might you test some of these ideas?
Question: Do seeds dropped from higher disperse farther, and if so, might this be one of the main benefits of plant height?
Season: All year, as noted.
How To Do It: A brief introduction about dispersal: seeds that disperse farther have a chance of locating suitable habitat for growth; also they escape from predation (see above). Plants whose seeds don’t disperse far are unlikely to colonize new habitats easily. Thus, a plant whose seeds disperse a bit farther than those of its neighbors is likely to have an advantage.
The exact nature of this activity will vary with the plant species.
Spring: Red maple (Acer rubrum) and box elder (Acer negundo) are great. First determine how these seeds are dispersed. Do they normally fall in pairs, or separated? Green or brown? Then students grab handfuls of red maple seeds and drop them from various heights: waist height, head height, top of slide height, and if possible from even higher, in a two story school.
An equal number (probably several handfuls of 10 20 seeds each) is dropped from each height on a breezy Spring day, and the resulting pattern of landings is mapped. Students also have fun watching the seeds whirl in the wind.
Wild germanium (Geranium carolinianum, also called crowsfoot) is an explosive disperser. Wild geranium infructescences that are nearly dry can be mounted at various heights (use bottles, etc.) from 1 centimeter to approximately 15 centimeters (as high as they get) above a cross made of two perpendicular strips of flypaper. When they explode (hours, days, or weeks later), the resulting pattern can be mapped.
Fall: Same with partridge pea (Cassia fasciculata): Use heights from 5 to 50 centimeters. Use pods that are almost but not quite dry. They should dry quite rapidly indoors.
Any Season: Dandelions or other parachute seeds. Let students blow the seeds from a lying down position, squatting, and kneeling. Note how far they go (don’t use flypaper here, just watch the seeds); or do it outside, and let the wind be involved. There are many other explosive or wind dispersed seeds around, but this should be sufficient.
48. The One That Got Away
Question: Do ant lions of different sizes differ in their ability (or desire) to capture ants of different sizes?
Season: All year.
Framework: II-5-A (II-5-B, I-3-C-ii).
Needed: Ant lion pits of different sizes, and ants of different sizes (should be extremely easy to accommodate this need).
Notes: See Activity 37. Do not use pits where there is obviously no ant lion, or a sleeping ant lion, or a scared ant lion. Clipboards, pencils, and paper.
Background Information: See Handbook page 69.
How To Do It: Scrutinize available pits in a patch, and choose a number of them in the “small” size range, and a number in the “large” range. Drop small UNDAMAGED ants in both kinds of pits. Note whether the ant lion even tries to grasp the ant or not, and if so, whether or not it is successful. Then do the same with large ants.
Discussion: Do large ants usually escape from small pits? From large pits? Then, why don’t small ant lions dig large pits? Look at energy questions in Activity 37. Now, are there any large ant lions (i.e., large pits presumably housing large ant lions) that ignore small ants but grab large ones? Why might this be so? Again, think about energy return per energy expended.
49. Androcles and the Antlion
Question: Do some kinds of ant lion foods escape more easily than others from the pits? Is there a relationship between escape-ability and the frequency with which the prey encounters ant lions?
Season: All year.
Framework: II-5-B (II-5-A, I-3-C-ii).
Needed: Ant lion pits of different sizes, and a variety of insects of different shapes and sizes. Clipboards, pencils, and paper.
How To Do It: Find a series of active ant lion pits, of medium to large size. Try dropping all sorts of small insects in them: ants of different species, beetles hanging around pits, small moths, bugs, etc. Note the results.
Discussion: Are there some that easily fall prey to ant lions? Can you spot any behaviors that tend to make them easy meat? Are there some that seem to escape frequently? Any traits associated with this? Do they sit still, then make a rapid dash for the rim? Do they have a hard “shell”? Are there any insects (e.g., brightly colored true bugs) that ant lions start to grab and then reject? Why might this be so? Might the bright color indicate bad taste? Is there any relation to the site from which the potential prey come; i.e., are those insects normally found near ant lion pits especially good at escaping? Are insects that don’t normally encounter ant lions especially vulnerable?
Extension: You might want to restrict some of the tests regarding the last question to ants alone: Test the ants that normally scavenge around ant lion pits from those that normally occur well away from them. If so, though, make sure that the ants are all about the same size, or you’ll be back in Activity 48.
50. The Pit of Despair
Question: What kinds of insects do ant lions eat?
Season: All year.
Framework: II-5-B (II-5-A, I-3-C-ii).
Needed: This requires ant lion pits that have at least a few former victims scattered around the rims; someone will have to do a brief survey first.
Background Information: Note that ant lions throw carcasses to the rim of the pit, so that by examining pits you get an idea (probably a somewhat biased one) of what ant lions have been eating.
How To Do It: So, have students simply go around looking at what has been eaten (I guarantee not just ants), and looking for interesting features of the prey that have been consumed, noting these.
Discussion: Are the already-consumed prey all dull colored, or are there some brightly colored ones? What kinds of insects are there? What sizes? Are there any really hard bodied ones? Do pits of different sizes have different arrays of victims, and if so, how do the arrays differ? Etc. etc.
51. The Bigger The Better?
Question: Do bigger spiders spin bigger webs that catch bigger (or more) prey?
Framework: II-5-A (I-3-C-ii).
Needed: Meter stick, rulers marked off in ler close (these spiders won’t bite); (b) measure the web diameter in centimeters or in millimeters; © measure inter strand distance, i.e., the distance between two successive “circles,” halfway between the center and edge; (d) count the number of prey in the web; (e) measure the length of each prey item in millimeters, and add up, for “total length of prey.”
Discussion: Compare rankings of numbers. Do bigger spiders spin wider webs that catch more prey, or a greater total length of prey? Do bigger spiders have a larger inter strand distance? How might this be accomplished? Does a larger inter strand distance mean that the size of the average prey (not the total length of prey) is greater? Why don’t small spiders catch big prey too, then? Etc. etc. Let students relate the different discoveries.
52. A Bag of Tricks
How do caterpillars, which are essentially little bags of bird food, avoid becoming prey?
5.b (5.a., 3.b.ii., 5e).
Caterpillars are meat on the hoof (proleg): nice soft packages of juicy bird food. And indeed many, many caterpillars are eaten by birds. But the caterpillars aren’t just “sitting ducks.” Different caterpillars have a wide variety of traits that make them less likely to be discovered by birds; or that enable them to escape when birds do find them
; and that make them less likely to be eaten by birds even when they can’t escape.
How To Do It:
Go on a caterpillar hunt. Look everywhere, but especially in weedy vegetation at the lawn’s edge; in shrubs; second-growth; at the edge of woods; under and on the leaves of schoolyard trees. Unsprayed and feral gardens are caterpillar factories.
For each caterpillar found, observe the following:
Is it sitting out in the open, or is it somewhat hidden?
Is it on the top or the bottom of a leaf?
Is it brightly colored or does it “blend in” with the color of the vegetation on which it sits?
Is it camoflaged within a mound of “frass,” or caterpillar feces?
Is it sewn up inside a leafy case, either made by rolling up one leaf and stitching it or by stitching two leaves together?
If hidden inside stiched leaves, has it also included some food supply (a leaf inside to munch), or do you think it might come out at night, when birds aren’t around?
Has it camoflaged its leaf nibbles in any way (after all, one way a bird could spot caterpillars would be to look for leaves with holes in them)?
Is there evidence that it eats just a little of one leaf before moving to the next?
What is its behavior when you approach it or touch it with a stick—does it drop to the ground on a silken thread, does it rear its head, does it regurgitate some noxious smelly gunk, does it imitate a snake and “strike” at you with what is actually its butt?
If it is brightly colored, do you think it is good to eat? If brightly colored, is it fairly unresponsive to your probings?
Is it bald, or covered with hair/spines (don’t touch!)?
If in a group, does the group exhibit some sort of confusing response when one is probed?
What other colors/ behaviors/ protuberances/ secretions do you see? There really is a tremendous variety of caterpillars in our area, from wonderful snake mimics to extraordinarily brightly colored (and noxious) sluggish ones to ones that drop to the ground at the slightest threat to wonderfully cryptic twig-like ones, and a thorough search by students will turn up all sorts of surprises.
Have students discuss caterpillar traits in the light of the threat of bird predation. Why haven’t all caterpillars “come up with the same solution” to that threat? Why are there so many different kinds of defense? Do some caterpillars appear to have several lines of defense
, such as: first, be cryptic; if discovered, drop; if discovered again, secrete smelly gunk?
A Scary Face?
“of the ... swallowtails ... all have a whitish ...[tail] end with some dark markings. When viewed from the side, the white patch and markings seem to simply form part of the overall disruptive color pattern.... But when viewed from behind (the view that a predator stalking a larva along a branch would see), false face patterns are clearly evident…
“The Giant Swallowtail and Bahama Swallowtail have similar ...false face patterns consisting of two small eyes, nostrils, and a downturned mouth. The Schaus Swallowtail has quite a different, skull-like pattern....
Others are colored so as to minimize cues to the predator, cues that indicate that they are indeed an insect at all. ” (The former is called “aposematic coloration”, the latter, “cryptic”.)
--Marc C. Minno and Thomas C. Emmel, Caudal false face patterns on the larvae of Florida swallowtails, Tropical Lepidoptera, 1992, Volume 3, issue 1, page 51.
53. Close Encounters
Question: Do birds attempt to eat some kinds of butterflies more than others, and why?
Season: F (mid October best).
Framework: 5.b. (5.f).
Needed: A weedy schoolyard edge or a flowering hedge where butterflies of several species congregate in the fall.
How To Do It: Students simply get within a meter of a fluttering, basking, or feeding butterfly and look for the presence of obvious bird beak marks on one or both hind wings. Beak marks are obvious ragged tears or V-shaped notches missing from the wing; most are exactly the shape of a bird’s beak. About 10% of fall butterflies have them, but the % varies among species. Using the field guide entry on “Butterflies” as well as the Golden Nature Guide to butterflies, students will determine the frequency of beak marks in different kinds of butterflies and relate these to other butterfly traits. Most likely butterflies are: cloudless sulphurs (most common, vary widely in tastiness—some are very noxious tasting to birds, many aren’t); other sulfurs (probably mostly tasty); buckeyes (probably tasty); gulf fritillaries (very nasty tasting); zebras (uncommon, very nasty tasting); woodnymphs (tasty). Do not bother with skippers; it’s hard to distinguish beakmarks from ripped-off tails, and their wings are harder to see.
Discussion: Ask students to note how the butterflies “look” and fly; do they fly slowly as if they hadn’t a care in the world, flaunting their colors, or do they fly fast and erratically (presumably hard to catch), or are they cryptic and hard to see, dropping often to the ground? How do beak marks correlate with tastiness? with flight mode? What is the explanation? How would you test this?
NOTE that the underlying assumption is that a beak mark represents an unsuccessful predation attempt, where the bird tried to consume the butterfly but the butterfly ripped away. An equally valid assumption is that beak marks represent cases where the bird tasted, then rejected the butterfly, whereas butterflies tasty to the bird were more often caught and consumed entirely. Probably the two causes can’t be distinguished, but for our purposes it’s enough to point out that beak marks are the result of a predation attempt, that different butterflies with different “tastiness,” color, and behavior have different frequencies of beak marks, and to let students speculate as far as they wish.
54. Things that Don’t Hide in Dark Corners