Descriptions like these have yet to make it into the standard school texts but could, by some stretch of the imagination, link to the key stage 4 requirement "to consider and evaluate the benefits and drawbacks of scientific developments, including those related to environment, personal health and quality of life and those raising ethical issues".
Nevertheless, we can supplement the information and build on pupils' curiosity.
The gruesome world of flukes, tapeworms and roundworms can be dealt with at many levels. Their external features and suitability for a life in a dark, silent world surrounded by food, faeces or blood can be explored at KS2 and KS3. At KS4, a more detailed analysis of adaptation could be tackled and at ASA2, classification of Platyhelminthes could be linked to work on variation and ecological niches.
Many pupils will have been stung by nettles or even cut by grass (probably Deschampsia caespitosa) but most will not have seen the surfaces of plants like sedge or lady's mantle through a lens. In an investigation at KS2 or KS3, the roughness of the sedges could be compared to glass paper.
Humans have exploited the alkaloids of plants for years and, as a result, we can get morphine from poppies, quinine from cinchona bark and salicylic acid (aspirin) from willow. Plenty of reference books have detailed summaries; for example, Seeds of Change: five plants that changed mankind by Henry Hobhouse (Pan Macmillan, pound;10.99) tackles quinine. Human parallels can be drawn with herbal remedies and alternative therapies (see www.homeopathy.co.uk). Other information is available from Kew Gardens (Tel: 020 8940 1171).
The disadvantages of using drugs to alleviate parasites and advantages of using scourers to de-worm can be linked to the long-established discovery of DDT-resistant mosquitoes and the spread of malaria.
There are lots of readers for primary and secondary pupils on the history of medicine and most deal with the development of medicines, drugs and treatments. The series History 13-16 has several relevant books, as does Medicine Through Time (ISBN-0431-057710).
You are unlikely to enjoy first-hand observations of the behaviours described. You might see birds swallowing small stones or gravel to supplement the digestive grinding mechanism of their gizzards. And experiments with woodlice and maggots and their responses to light could be linked to second-hand data on conditioning in mammals.