PURPOSE:  To determine if invertebrates are active under the snow in winter.

MATERIALS (per group): Field -- hand shovel, pencil, pitfall trap, trap covers (wood or shingle, about 30 cm square), antifreeze mixture (ethylene glycol and water), stake and flagging tape, meter stick, flat pan or box for teacher.  Lab -- stereo/microscope or hand lens, filter paper, funnel, petri dish, dissecting needle, eyedropper.

INTRODUCTION:  The soil litter layer is composed of organic debris like leaves, twigs, and dead animal parts -- not fast food wrappers or cigarette butts!  The invertebrates that live in this ecosystem are important as decomposers.  Decomposers recycle nutrients back into the environment as they consume the organic debris on the ground.

When these animals are active in the soil litter, they can be caught using a pitfall trap.  Each pitfall trap consists of two cups.  One is a permanent outer cup set level with the ground.  A removable inner cup is filled with a preservative.  The whole trap is covered with a loose lid to keep debris from filling the cups, while allowing the invertebrates to crawl beneath.

In the warm months of the year, pitfall traps rapidly fill up with unwary invertebrates moving over the ground under the litter.  In this activity, you will place pitfall traps filled with antifreeze liquid under the snow to determine if invertebrates are active in winter.

PREDICTIONS: Use what you know about the activity of invertebrates in summer, the cold temperatures of winter, and the insulating effect of snow to make a prediction.

1.  Do you think you will find many soil invertebrates moving around under the snow? Explain your ideas.

PROCEDURE:

A. In autumn before snowfall, your teacher will show you where to establish your pitfall trap as follows:

(1)  Carefully remove the soil litter from the area.  Install the outer cup only of the pitfall trap level with the soil surface.

(2)  Place the cover over the trap.  Prop it up about 1 cm on some stones as shown in the diagram. Replace the litter over the trap.

(3) Mark the location of the trap with the stake and flagging tape.  Draw a sketch of your study area showing the location of the trap, vegetation, and other features.

B.  After there is snow on the ground, return to your trap site and dig down to the trap cover.  Do not trample the snow around the trap.

C.  Write your name on the inner cup.  Set the trap by filling the inner cup half full of antifreeze mixture and placing it into the outer cup.

D.  Replace the cover and the trap marker. Cover the trap with snow. Do not pack the snow. 

E. After at least 10 days, return to your pitfall trap.  Measure the depth of the undisturbed snow near your trap. Record the snow depth in centimeters on the cup.  Carefully dig down to remove the inner cup.  Give the cup to your teacher for safe-keeping.  Remove the entire trap, fill in the hole, and replace the snow.

F.  In the lab, transfer the snow depth measurement to your data table.

G.  Pour the contents of the cup through a funnel lined with filter paper.  Spread the filter paper on a petri dish. View with a stereo microscope or hand lens, using the dissecting needle and eyedropper as needed.

H. Count the total number of invertebrates found in your sample.  Record your data on the data table.

I.  If you found invertebrates in your sample, identify them using the picture key provided.

J.  Share your data with the class.  Record class data on your data sheet.

YOUR DATA:

Sample Location:________________________________________________________

Snow Depth (cm):____________ Total # Invertebrates in Sample:___________________

Kinds of Invertebrates in Sample:____________________________________________

_____________________________________________________________________

_____________________________________________________________________

CLASS DATA:

CONCLUSIONS:

2. Are soil invertebrates active under the snow in winter?  Use class data to support your answer.  Was your prediction correct?

3. Which location contained the most invertebrates?  Which location contained the least invertebrates? 

DISCUSSION:

4. What environmental factors could account for the differences in number of invertebrates in different locations?

5. Does the activity of invertebrates vary with the depth of the snow?  If so, what is the relationship?

6. Why don't invertebrates freeze under the snow?

7. If the snow were packed down by cross country skiers or snowmobiles,  how do you think this would affect invertebrate activity under the snow?  What effect do you think this would have on the survival of invertebrates in winter?

8. What do you think soil invertebrates eat?  Explain your answer.

                 KEY TO ADULT SOIL AND LITTER INVERTEBRATES

 1a.  Body segmented..........................................................2

 1b.  Body not segmented, usually with a coiled shell........Gastropoda (snails)

 2a.  Appendages segmented....................................................3

 2b.  Appendages if present not segmented.............Annelida (segmented worms)

 3a.  Antennae present........................................................7

 3b.  Antennae absent.........................................................4

 4a.  Three pair of legs................................................Protura

 4b.  Four pairs of legs (pedipalps in front of legs and may appear leg-like..5

 5a.  Pedipalps with pincher-like claws, abdomen segmented....Pseudoscorpionida 
                                                               (pseudoscorpions)

 5b.  Pedipalps without pincher-like claws, abdomen not segmented..    .......6

 6a.  Cephalothorax and abdomen joined by a narrow connection..Araneae (spiders) 

 6b.  Cephalothorax and abdomen joined by a broad connection.....Acarina (mites)

 7a.  Three pairs of legs....................................................12

 7b.  More than three pairs of legs...........................................8

 8a.  Distinct head followed by a series of segments..........................9

 8b.  Distinct head absent....................................Isopoda (pillbugs)

 9a.  9 - 12 pairs of legs...................................................10

 9b.  More than 12 pairs of legs.............................................11

10a.  Antennae branched...............................................Pauropoda