April
Seasonal snapshots of nature in close-up
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.
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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Contents
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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Contents
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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Contents
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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