Seasonal snapshots of nature in close-up

This month's features:

Please read the important notes on collecting.

The days are getting longer and the spring flowers are beginning to show. The naturalist will soon be spoilt for choice of subjects to study in close-up with both the hand lens in the field and for the microscope back home.
The recurring theme in these seasonal nature studies is that even the commonest things in nature offer a whole new world to study when examined in close-up. So this month we examine the humble daisy, the mosquito you love to hate and lichens.

Mosquito antennae

The mosquito (family Culicidae) hardly needs introducing, the itchy swelling resulting from the female taking a tasty snack of your blood is familiar to everybody. However, mosquitoes and other small flies are fascinating in close-up, either with the hand lens or low power stereo microscope. A good source of them for study is any spiders web left over from last season eg in the shed or garage. Webs are also a rich source of other insects to study. The webs in my garage for example are full of green lacewings (family Chrysopidae).

The image above is the antennae of a male mosquito. The line drawing at the head of this page is the head of a male mosquito (genus Culex). It is easy to tell a male from a female mosquito because the male usually has bushier antennae. The antennae is a marvel of nature's engineering. True flies (Diptera) have hearing and for the mosquito the 'organ' of hearing is at the base of the antennae. The base is expanded to form a sac containing a large number of sensory units called scolophores. These are stimulated by vibrations of the antennae shaft.

The male mosquito is sensitive only to the humming frequency of the female of his own species, and he will fly in the direction of such sound to mate with the female.

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Lichen - fungi and algae cooperate

Until the advent of microscopy, lichens were classified as a single organism. But early studies revealed that lichens are a close association for mutual benefit of algae and fungi ie symbiosis. Lichens occur in a range of morphologies and colours, from the attractive crusts growing on gravestones or rocky seashores to the leafy forms found on trees.

Lichens are very slow growing and should not be removed from a substrate (particularly rocks or gravestones) but examined in situ with a hand lens. If a dead twig or piece of bark has fallen off a tree and has lichen growing on it, small pieces can usually be taken for study at home without damaging a habitat. (But see Important Notes on Collecting).

The lichen shown right was found on a dead twig (species uncertain). Examine habitats such as tree bark, fallen branches, heaths, gravestones, rocky seashores - each habitat usually has distinctive species if you live in an unpolluted area. Lichens have assumed an important role in pollution monitoring because many species are intolerant to air pollution such as sulphur dioxide.

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The daisy - a composite of flowers

Like me, you have probably walked passed the humble daisy (Bellis perennis) or it's relatives in the Compositae family many times without a second glance. But it is well worth studying under the 10X lens and low power stereo microscope. As the family name suggests it is not a single flower but a composite of flowers. The best way to appreciate this is to cut a flowerhead in half with a knife along the axis of the stem. The image on the left above shows a split flowerhead.

Each yellow tube is a separate flower or floret with male and female parts when open. Some of the florets in the above image are not open. The yellow florets that form the central yellow head are called disc florets, whereas those that have a single petal that collectively form the white ring of petals are ray florets.

It is interesting to compare the structure of the daisy with another flower seen at this time of year - the dandelion (Taraxacum). This flower only has ray florets ie each floret has a single yellow petal. This is why the dandelion doesn't have the central yellow disc that the daisy has. Try splitting a single floret open with a knife to study the flower structure.

Why not join me next month to study nature in close-up in Spring?

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Suggested reading

Your local library should have introductory texts on botany that should explain the structure of flowers of the Compositae family and the symbiotic relationship of algae and fungi in lichens. The larger encyclopaedias such as Encyclopaedia Britannica are also worth consulting.

The line drawing at the head of this page was taken from L C Miall's Aquatic Insects, Macmillan, London 1912. This is a delightful book with excellent line drawings...worth looking out for in the secondhand bookshops.

Image details

Images were taken using a CCD camera attached to the eyepiece tube of a stereo microscope using a x1 paired objective with no eyepiece. Camera images were transferred to the PC using a Creative Video Spigot capture card.
Image manipulation using Photostyler v2.0 software.

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