Category Science

When do dragonflies eat?

Dragonflies are impressive insects with two pairs of powerful clear wings which enable them to catch insects on the wing. They have large eyes for spotting their prey. Dragonfly nymphs live in water and so the adults are usually seen near ponds, rivers and lakes. Some species have a feeding territory which they guard from other dragonflies – their clattering wings can sometimes be heard as they battle. When they mate, most species fly around in tandem before they lay their eggs in the water or among the waterside vegetation. Dragonfly nymphs are active carnivores. They feed on other insects, but can catch tadpoles or even small fish. On the underside of the head is a flap called the mask. This is armed with sharp jaws and fangs. At rest it is folded, but it can shoot out to catch its prey.

Fact File:

A dragonfly’s eyes are large and five it almost all-around vision. They are sensitive to the slightest movement around them. If you look closely you will be able to see the individual facets of the eye. Each one contains its own lens; together they help form the image seen.

 

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When do caterpillars turn into butterflies?

Young insects develop in two main ways. Butterflies, bees and beetles, go through a process called metamorphosis. This means that their eggs hatch into larvae or caterpillars. Later these become a pupa or chrysalis, within an imago, or an adult insect, develops. The larvae may live in a different habitat from the adult and require different foods.

In species such as grasshoppers and locusts, the young that hatch from eggs look rather like small adults, and are called nymphs. As they grow, the nymphs shed their skins, looking more and more like adults each time.

Fact file:

The wings of a bee or wasp can beat as many as 250 times per second during flight. The wings of midges can beat as many as 1,000 times per second – which accounts for the high-pitched whine that these tiny insects make.

 

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When do plants eat insects?

Plants growing in bogs and peaty areas often need to supplement their food supply by catching insects. Bog water contains very little nitrogen, but some bog plants can obtain this substance by catching and digesting insects. They are known as insectivorous plants. Other insectivorous plants are covered with sticky tentacles that trap flies. The most remarkable is the Venus flytrap plant. It has two clawed plates that slam together when a fly walks over them and touches a trigger hair. Other insect-eating plants are aquatic, catching tiny crustaceans in bladder-shaped underwater traps. Some of the largest insectivorous plants live in the tropical rainforests.

Fact file:

Some insects use camouflage to blend into their environment, protecting themselves from predators. 

 

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When do trees lose their leaves?

A tree that loses its leaves in winter is called a deciduous tree. Trees that are about to lose their leaves in the autumn conserve their food supplies by withdrawing all the nutrients from the leaves. Chlorophyll is broken down in the leaves, causing their pigment to change. Eventually all the nutrients are moved from the leaves and they wither, turn brown and eventually fall from the tree.

Fact File:

Every year a tree grows, it deposits a new layer of cells on the outside of its trunk, beneath the bark. This new layer is called an annual ring. By counting the annual rings it is simple to work out the exact age of a tree.

 

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When does pollination take place?

Pollination is the process of transferring pollen from the stamen to stigma. It is possible for flowers to pollinate themselves, or other flowers on the same plant – this is called self-pollination. It is, however, much better for the health of the species if cross-pollination occurs, i.e. pollen is transferred from one plant to another. The most common method involves insects that are attracted to the flowers for their nectar. Pollen grains stick to the insects’ bodies and are effectively transferred from one plant to another as the insect moves from flower to flower. Other, less attractive types of flower, use wind to transport their pollen.

Fact File:

The flowers of orchids are highly specialized for pollination by insects. When the insect pushes into the flower to reach the nectar, the pollinia stick onto its head.

 

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When are seeds formed?

Seeds are the main means by which flowering plants reproduce and spread. After the plant has been fertilized the egg cells develop into a seed from which a new plant can develop. The seed contains an embryo from which the new plant will grow. It also contains a food store to nourish the embryo until it has developed roots and leaves. The seed is enclosed in a tough outer coating to protect it from drying out. Many seeds can be carried by the wind. Some even have a fluffy umbrella like the dandelion seed head, which enables them to be carried for very long distances.

Fact File:

The biggest seed is the coco de mer, a kind of coconut that grows in the Seychelles, a group of islands in the Indian Ocean. The coco de mer seeds weigh 250 kg each.

 

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