The Open Door Web Site
Part XIX : Colonizing and Populating Habitats :
Cabbage White Butterfly
Female great green bush-cricket showing ovipositor
COLONIZING AND POPULATING HABITATS
The butterfly represents the adult (mature) stage
In order to colonize new habitats animals must be able to disperse themselves. In this section we are going to study the invertebrates and their life cycles. We often find that a particular stage in the life of an invertebrate is adapted for dispersal. Other stages in the life cycle may be adapted for feeding and growth. This means that the animal has to change its form as it grows.
The change in the form of an animal as it grows and develops is called metamorphosis. To remind you "Metamorphosis" comes from the Greek and it means "a change in shape".
It is the adult form of insects which is responsible for their dispersal because by that stage they can usually fly. Some of the best known examples of insects which disperse themselves widely are considered as pests, for example the cabbage white butterfly and the locust. These insects do a lot of damage to our crops so they have been very carefully studied.
Metamorphosis in Insects
In Europe the cabbage white butterfly is estimated to fly between 100 and 200 km in its brief adult life span of two weeks. In Africa the desert locust can spread out over almost 30 million square kilometres during the years when there is a plague of locusts.
Searching for food
It is on these long journeys that the adult female insect searches for suitable places to lay her eggs. In the case of herbivorous insects, such as the cabbage white butterfly, this means looking for the correct food plant for her offspring. To help them in this task the adult insects have good colour vision.
The female cabbage white butterfly is attracted to red-blue colours when she is young. This is so that she can identify flowers where she will drink nectar. When she is ready to lay her eggs the female butterfly is attracted to yellow-green colours or blue colours. These are the colours of the food plant where she must lay her eggs. She may sometimes even mistake a yellow tee-shirt for a food plant ...until she gets close enough to smell it or taste it!
To taste the food plant butterflies use their legs; a brief half-second touch is enough to tell the female whether it is the food plant that she is searching for.
The female insects often have specialized egg-laying organs at the end of the abdomen. These are called ovipositors and they come in all shapes and sizes depending upon the material the eggs are going to be laid in and the depth at which she will lay the eggs.
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