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The Milkweed : A Micro-habitat The study of a milkweed plant gives a fascinating picture of a micro-habitat. A micro-habitat is a very small area which is home to a community of organisms. The milkweed plant grows to about 90cm in height. It is called milkweed because it produces a white liquid, called sap, when its stem is cut or broken. Many animals live their lives on the milkweed plant or visit it to feed. The milkweed flowers produce a sugary nectar to attract insects such as the honeybee and the bumblebee during the day. At night, the white flowers produce more scent and nectar which attracts moths.
The caterpillars of the monarch butterfly only eat the leaves of the milkweed plant. The leaves contain a special chemical which makes the larvae and the adult butterfly unpleasant to eat. This gives them protection from predators. The crab spider is white in colour which camouflages it when it is on the milkweed flower. The crab spider preys on the insects which visit the milkweed. When the milkweed flowers are in bloom, the crab spider can eat enough prey to increase its mass from 40mg to 400mg in 2 weeks. The remains of the crab spider's prey fall to the ground. These carcasses become the food for a scavenger called the harvestman. At night, the harvestman climbs up the stem of the milkweed to feed on the carcasses which did not fall to the ground. The crab spiders lay their eggs on the underside of the milkweed flower petals. The eggs are grouped together in an egg sac. Some flies and small wasps lay their own eggs in the crab spiders egg sacs. When the larvae of the flies and wasps hatch, they grow by eating the eggs of the crab spider in the egg sac. The seeds of the milkweed develop in pods. Each pod contains 100 to 200 seeds which are dispersed by the wind. The milkweed bugs feed on these seeds. Finally, aphids use their pointed mouthparts to pierce the stems and suck out the white sap.
The Rocky Shore
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© Paul Billiet and Shirley Burchill 2009 |
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