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Thinking outside the box - Investigating Invertebrates
By David Hanson
17 Apr

David Hanson has over 40 years' experience of teaching, has been a member of the ISEB Mathematics exam setting team and has written numerous titles for Galore Park, including the Mathematics for Common Entrance 13 Plus revision series. 


Small invertebrate animals are abundant in many habitats. Usually, we find them in their daytime hiding places. It is interesting to investigate their activity in their natural habitat and we can do this when we are not watching!

We are most likely to encounter arthropods:

  • woodlice (14 legs)

  • centipedes (more than 14 legs and one pair of legs on each body segment)

  • millipedes (more than 14 legs and two pairs of legs on each body segment)

  • spiders (8 legs)

  • harvestmen (8 very long legs and small body)

  • insects, particularly beetles (6 legs)

but we might also meet

  • slugs and snails (molluscs)

  • earthworms (annelids)
     

The Basic Technique
We prepare a glass plate by making a fine, sooty deposit on it. The glass plate is placed, sooty side up, in a suitable position. After a time (for example overnight) the plate is likely to show the tracks of animals.

sooty glass


Preparing the Basic Equipment
Prepare a cover. This can be made by cutting away sections of the four edges of an old rectangular ice cream container, or similar, leaving the corners to act as legs.
Obtain a small glass plate. About 15 cm x 10 cm would be ideal, but the exact size does not matter. The glass from a photo frame would be fine but check that it is free from cracks.
You also need:

  • a candle (or tea-light)

  • a candle holder (or tea-light holder)

  • matches

  • an old dinner plate or similar

  • safety goggles

     

‘Smoking’ a Glass Plate
It is important that you choose a sensible, safe area to work. Hold the glass plate firmly at one end. Wearing safety goggles, ‘smoke’ the half of the glass plate furthest from you over a candle flame, slowly and carefully, keeping the plate about 3cm above the top of the flame and moving the plate constantly.

The half of the glass plate nearest to your hands should remain cold.

Despite all your care, a glass plate may crack, usually because one area became too hot. Don’t worry! Simply stop and try again with a different plate.
A thin, even deposit of soot about 6 cm in diameter would be fine. Leave the glass plate, sooty side up on an old dinner plate (or similar) to cool down.




Preparing a First Track
It is a good idea to have a trial run with a single animal, just to get the ‘feel’ of things.

  1. Place your cold ‘smoked’ glass plate sooty side up on a flat surface.
  2. Find a suitable ‘volunteer’ woodlouse, beetle or other arthropod.
  3. Place the animal on, or very close to, the sooty deposit and allow it to wander freely for a short time. Sometimes a little gentle persuasion is needed!

The animal will be grateful if you return it to where you found it. It may not be too happy about having dirty feet, but the soot will soon wear off!

bug on plate

Hold the glass plate up to the light and you should be able to see the tracks quite clearly.


Preparing a Permanent Record of a Track
There are two easy ways of preparing a permanent record of a track. The simplest way is to carefully lay a piece of clear adhesive tape over the track and press down with your finger so that the soot sticks to the tape. This can be fixed to a backing piece of white paper or card. A better way is to photograph the track with a digital camera. Place the glass plate over a light source (a ‘light box’ is ideal, but just holding it over a lamp will do). Using the computer, you might like to produce a negative image.

Making a Reference Collection of Tracks
To be able to identify the animals which made multiple tracks on a plate left overnight, it is a good idea to prepare a reference collection of tracks using known animals. With a good reference collection, and practice, it should be possible to say which types of animal were active, at a particular time, in a particular microsite.
 
Studying the nocturnal activity of invertebrates
Place a smoked plate in a suitable location and cover it. Leave this overnight and then check the next morning to see if any animals have left tracks in the soot deposit on your plate. You may be surprised!



A few suggestions
You may like to

  • ‘bait’ a glass plate with a small piece of apple, or some other food, to see if animals are attracted to it.

  • compare the activity of invertebrates

    • in one habitat on several different nights

    • in several different habitats on the same night.

with several sets of basic equipment (glass plate and cover)

Remember to keep a record!

Investigations like this are imporant in developing your child's scientifc mind and will help towards covering all aspects of the ISEB Science syllabus. Our revision range is also a great way to ensure that your child is fully prepared ahead of examination, you can buy all three Science revision products together for 20% than if you purchased separately 

science pack
 

Tags: 11+, 11 plus, 11plus, 13+, 13, 13 plus, blog, challenge, David Hanson, games, Science

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