Minibeasts_Concept_2

Subject Facts

Two forms of insect metamorphosis are recognised by most entomologists: complete and incomplete. The butterfly is an example of a complete metamorphosis: the animal progresses through an immature, larval stage before changing via a dormant pupa stage, into a mature adult (see Figure 2). The coat protecting the pupa is commonly known as a cocoon.The change from larva to adult allows the animal to adapt to changing seasonal conditions and make use of very different food supplies.

An incomplete metamorphosis is where the young and adult forms are not very different: often the immature form only lacks wings and sexual organs. in this case, the young form is called a nymph (see Figure 3). Again, the changes are adaptations to make use of changing habitats and food supplies. The mayfly, for example, spends one to three years as an aquatic nymph, eating and growing. Mayfly nymphs will emerge (all at the same time) from the water, shed their nymph skins and have a very short life as a winged insect — usually about 48 hours (long enough to mate). Not surprisingly, the group (or order) to which mayflies belong is called the Ephemeroptera (meaning 'short-lived wings').

Why you need to know these facts

Many arthropods (and insects in particular) provide excellent examples of metamorphosis: they undergo radical changes in their body structure, lifestyle and habitat as they move from one stage of their life cycle to the next. Without careful study, children are likely to assume that caterpillars and butterflies, for example, are completely different animals. The processes of insect metamorphosis can be observed over a fairly short period of time, and provide a useful introduction to the idea of biological development.

Vocabulary

Larva — an immature form which bears little resemblance to the adult form.

Metamorphosis — a process of change from one form to another during a life cycle.

Nymph — an immature form that bears some resemblance to the adult (the differences are usually that the adult form has wings and reproductive organs, and has a different habitat and food source).

Amazing facts

Dragonflies shed their skins up to 20 times as nymphs where they live in ponds and streams. The nymphs can grow so large that they are able to feed on tadpoles and small fish. The protective covering or cocoon around a butterfly or moth pupa is spun out of a kind of silk, which is allowed to harden.

Silk cloth is made from threads spun by the silkmoth caterpillar.

Common Misconceptions

Butterflies die in the winter.

You don't see them around because of the lack of food Many butterflies lie dormant over the winter months. A very few, such as the painted lady, migrate as some bird species do: in summer, they can be found as far north as Finland; in winter, they fly to southern Europe and North Africa. Relatively speaking, it is probably the most amazing migration of any animal

Questions

What is cuckoo spit?

At its larval stage, the froghopper (a type of aphid related to the greenfly) lives by sucking juice out of plants. To prevent it from drying out (and to deter predators), it surrounds itself with a froth which it produces from its anus, So the name could have been a lot worse.

Do earthworms reproduce by dividing? No, If a small portion is cut off the head or tail, the worm can regenerate the missing portion — but the smaller part dies.

Worms are hermaphrodites (each individual has both male and female sex organs), but the individuals usually pair up to fertilise each other. (This increases genetic variation, and is therefore good for the species,) Each individual will lay eggs, wrapped up in a cocoon, from which small, fully developed worms will emerge.

Teaching ideas

It is possible to keep some types of insect in captivity in order to observe their metamorphosis. Be Safe! (ASE Publications) provides a complete and very useful list of these animals.

Particular species of butterfly are excellent for this purpose, as are certain cockroaches and stick insects. Eggs, along with suitable habitats and food (plants), can be obtained from butterfly farms. A class project on insect metamorphosis will allow the children to observe and record the various stages, then release the adult insects into a local environment that has been prepared with the appropriate plant life to sustain them.