Lesson Title: Looking at a Snake Unit: Classification (Extension)
Aim: To show how the features of an animal relate to its lifestyle, habitat, etc., and introduce some basic evolutionary ideas if desired.
Note: This is an optional lesson, to be added if it is felt that it will reinforce the ideas presented in the unit. Obviously a suitable snake needs to be available for study; see safety considerations below. The lesson plan below relates to a corn snake (Elephas guttata), but can easily be adapted to most of the commonly kept snakes, and to other (preferably unfamiliar) animals if a snake is not available. Snakes with abnormal coloration (e.g. "snow corns") may not be suitable.
Key Words: Egg-laying (Oviparous), "warm blooded" (Homeothermic), "cold blooded" (Poikilothermic), Shedding
Introduction: Pupils should be warned in the previous lesson that the next lesson will involve a live snake, and positioned so that anyone exhibiting a genuine phobic reaction can leave the room easily. In rooms with a single entrance it may be advisable to have the snake in an opaque container (such as a vivarium covered with a box) away from the door before pupils enter the room. Take registers etc. before the snake is introduced.
Safety: Care should be taken to choose a snake that is "well behaved" when handled. Larger male corn snakes seem to be especially suitable, females are generally less willing to be handled. The snake should be fed 2-3 days before the lesson. A cloth and disinfectant should be available, in case the snake voids during handling. Check that the snake is not shedding or otherwise likely to be irritable. Some alcohol swabs should be available, or a bottle of alcohol and some cotton wool; if anyone is bitten the wound should be swabbed immediately, if the snake is unwilling to let go the alcohol will drive it away. Use a room that has a sink/wash basin, and provide antiseptic soap; snakes and other reptiles can carry salmonella, so anyone handling the snake must wash afterwards. The teacher MUST be familiar with handling and controlling the snake used for the lesson! Venomous snakes must NOT be used, even those allegedly harmless to humans!
Support

Make sure that any tutors etc. present are aware that the snake will be used, and are not phobic! Students may need more prompting in all sections

  1. As core.
  2. As core.
  3. As core.
  4. As core.
  5. As core.
  6. As core, but simplify terms used.
  7. As core.
  8. As core.
 Core

See detailed lesson plan below

  1. Visual examination of snake.
  2. Discussion of origin, habitat, etc.
  3. Discuss coloration as camouflage
  4. Discuss evolution and loss of limbs.
  5. Discuss methods of locomotion.
  6. OHPs, basics of snake anatomy and modifications to a normal vertebrate body
  7. Questions, students handle snake (if it is behaving) under supervision. Remind pupils
  • To avoid letting the snake contact their mouths or eyes
  • to keep fingers etc. away from its mouth
  • to avoid distressing the snake.
  1. Return snake to vivarium; pupils may wish to draw it, ask more questions, etc. if time permits.

    If a hatchling is available demonstrate the "rattling" response to apparent danger.

Higher Ability

Students should need less prompting throughout

  1. As core.
  2. As core.
  3. As core.
  4. As core.
  5. As core.
  6. As core.
  7. As core; this may be a good opportunity to explain what "cold blooded" (poikilothermic) and "warm blooded" (homeothermic) really mean, especially if the snake has had time to warm up, the scientific terms are probably inappropriate at this level.
  8. As core. If time permits some additional work might be appropriate; for example, measuring the snake by allowing it to move through a glass tube and simultaneously noting the position of its head and tail. Point out that several measurements may be needed to get the maximum and average extended lengths. Weighing (in a bag or box) is easier but less challenging.
H/W: Write about what it would be like to be a snake. H/W: Write about the snake's adaptations to its lifestyle. H/W: As core.
Citizenship: Wider awareness of environmental issues, e.g. snakes unjustly persecuted when they were in fact eating pests. The "Simpsons" episode "Whacking Day" has been shown on British TV, and shows how violent such persecution can be; snake "culls" of this type are common in parts of America.
Responsibility for keeping pets and handling them carefully.
Resources
OHP Far Side cartoon "God Makes The Snake" (Optional)
OHP Snake skeleton and basic anatomy (Grolier encyclopaedia)
OHP Photo of snake, size of jaw when dislocated drawn onto the picture.
OHP Jaw diagram (Grolier)
OHP Constriction (Grolier - may not be suitable for some groups)
Worksheet: Picture of snake body & scales (Biodidac)
Worksheet: Picture of snake mouth open showing teeth, trachea, etc. (Biodidac)
Video - The Trials of Life (set to correct place as below)

Vivarium, lamp, etc.
Corn snake - large placid adult
Hatchling snake if available (housed separately, not to be handled by pupils)
Egg cases, Shed skin
Antiseptic soap, towel, sink, alcohol swabs, disinfectant and cloth

For extended lesson (measurement)
Glass/plastic tube wider and longer than the snake (e.g. 1.5 metres x 40mm internal diameter)
2 Metre rulers
Balance with capacity to hold snake and a box or bag (e.g. 0-1kg x 1g)

Detailed lesson plan

Throughout the lesson it is likely that pupils will have questions related to the snake's anatomy, behaviour, mating habits, diet, etc. If possible they should be answered as they come up, if it will not disrupt the lesson too much. A common question is "how does it go to the lavatory?", since there is no obvious "bottom"; point out the vent and explain that wastes are released from an opening normally covered by scales. For higher ability explain that this corresponds to the position of the pelvis in limbed vertebrates.

  1. Show pupils the snake in its vivarium and lift it out to allow them to see it more clearly. Tell them its name (it helps if they think of it as a pet, not a strange animal)
  2. Explain that it is a North American corn snake, so called because the early settlers often found them in corn fields. Ask the pupils why it might be found there; elicit the answer that mice and other small animals eat corn, the snake eats them. Do not over-stress this point. Explain that snakes are reptiles; they lay eggs, and are "cold blooded" (this may need explaining at this or a later stage). Mention shedding of skin.
  3. Point out the vivid red and brown coloration, and ask why it has these colours; elicit the answer that they are camouflage.
  4. Ask why it has no limbs; elicit the answer that it has evolved (or is "designed") to chase other animals down tunnels, where limbs are likely to be less useful. Point out other animals that have similarly elongated shapes and vestigial or no limbs, which also chase prey through tunnels; ferrets and weasels, limbless lizards (such as Britain's slow worms), daschunds, etc.
  5. Point out methods the snake uses to move; elongation and compression of body, leverage around a stationary object, etc. Show that the body generally follows the movement of the head, although there are exceptions.
  6. Move to OHP and explain the basics of snake anatomy and the modifications to a normal vertebrate body involved:
  • Single lung (except some very old species)
  • Elongated trachea (including extension of windpipe into lower jaw)
  • Many ribs used for locomotion
  • Tongue used for smelling "in stereo"
  • Jaw structure (explain dislocation) - show TRIALS OF LIFE section of snake swallowing a slug (immediately after killer whale section).
    NB: Pupils should NOT be shown the snake feeding on a mouse, but should be aware that these animals eat their prey whole.
  • Compare shape and nature of teeth with other animals; elicit that they are designed to seize and immobilise prey prior to swallowing whole; there are no specialised slicing or grinding teeth for breaking up food. Comparison with killer whale teeth.
  1. Questions and allow students to handle snake (if it is behaving) under supervision. Remind pupils
  • To avoid letting the snake contact their mouths or eyes
  • to keep fingers etc. away from its mouth
  • to avoid distressing the snake.
  1. Return snake to vivarium for remainder of lesson; pupils may wish to draw it, ask more questions, etc. if time permits.

    If a hatchling is available it may be possible to demonstrate the "rattling" response to apparent danger. Point out that this is not imitation of a rattlesnake; it is seen in old world snakes as well.