Free From School Part 6

Dr Vijayalakshmi also bred a particular species of fly in a small cage with fine mesh with a small saucer of milk in the centre as a medium for breeding.

Baby spiders were also housed individually in bottles and these were fed fly larvae or the larvae which come when maida or rava begins to lose its freshness.

The purpose of all these experiments was to find out which types of spiders were useful for using as pest control agents to deal with c.o.c.kroaches. Information about spiders such as their growth, hardiness, their eating habits, reproduction etc. are important indicators of the species of spiders that can be kept in houses as predators for c.o.c.kroaches.

Other than the spider work I tried to learn Tamil from Selvan but he was keen to learn English from me and so both of us failed in learning a new language and ended up speaking a c.o.c.ktail of TamEnglish instead.

Extracts from Diary: Spiders

26th November: Uncle Mano and I left for Dr Vijayalakshmi's office this morning at 7 a.m. While Uncle Mano and Madam chatted, I read some books. Madam then showed us her spider collection. She also introduced me to Selvan. Before we left she gave me some books to take home to read.

27th November: Watched how Selvan separated baby spiders from their mother, placing each baby in a separate container. There were about 110 babies. Then we fed about 200 older spider babies. Selvan showed me how to check their moulting.

28th November: Today I did feeding of the spider babies on my own. Then transferred adults from one container to another and then fed them.

29th November: Today did only feeding of spider babies. Madam did not come to the office as she was ill but her husband Dr Balasubramanian came to check on us instead. Read some books on spiders in the afternoon. Left early for home as Uncle Mano and Aunty Sagu were going away for a few days and I would be staying at their relative Santosh k.u.mar's place instead. They left at 7.30 p.m. and I waited at their neighbour's place for Santosh to collect me which he did at 9 p.m.

30th November: Being Sunday I got up late and ate idlis, dosas and sambar for breakfast. Wrote out my diary for the past 2 days and watched some TV. In the evening Santosh took me to the bus stand and explained the route I would have to take next morning to CIKS.

1st December: Madam came to the office today and showed me how to collect spiders which were in the compound of the office. She also gave me some more material to read on spiders and told me to start preparing my essay on spiders. After doing a little bit of feeding as usual, I went out on my own and collected few species of spiders. Then Madam helped me identify them and also some other species of spiders that they had caught. Spent the afternoon catching flies to feed to some of the older spiders.

2nd December: Today I only did identifying of different species of spiders. I took some material home to read and so I left early; was so busy looking at the books I was carrying, I didn't notice the terminus where I was to get off and got over carried much further. Had to walk nearly half an hour back. Asked people for directions and finally reached the terminus.

3rd December: Did not feel well today so I didn't go to CIKS. Read the books I had brought at home. Started preparing my written report.

4th December: Today did feeding of spiders as usual. Then caught about 70 flies and fed them to the adult spiders. Put 2 spiders to mate and made my observations. Continued writing my report in the evening.

5th December: Went to New College to collect my vermiculture report.

6th December: Did feeding of baby spiders first. Then caught flies. A female spider's eggs had just hatched so Selvan and I did the separation of the babies into individual containers.

7th December: Did writing of my report first today. Then I gave it to Madam to correct. After she finished with it, I started writing it in fair. I finished writing the report before evening and left it with Madam for final approval.

8th December: Went to CIKS late as I had a bad stomach. I was given my final report signed and Madam also gave me a certificate. I left slightly early in the evening as I was still feeling unwell and was scheduled to leave for the Croc Bank the next day.

Field Work Notes: Spiders

These days most of us use Baygon or some other synthetic poison to control c.o.c.kroaches and other pests. But what does this do? It only makes c.o.c.kroaches or pests immune or resistant to such poisons.

Moreover, synthetic chemicals are very harmful and pollute the environment. How nice it would be if we had a biological method of controlling of pests. But that's just what spiders are!

A spider is not an insect. Insects are made up of a head, thorax and an abdomen. They have compound eyes and are six-legged. They usually grow wings in certain stages of their life and possess feelers or antennae.

Insects produce eggs which hatch into young that are completely different from their parents. The young ones usually grow through metamorphosis.

A spider on the other hand is an arthropod, made up of a cepolothorax joined to an abdomen. It does not grow wings at any stage of its life.

It is eight-legged, and in place of the normal insect antennae it has pedipalps. A spider generally has eight simple eyes or it could have six eyes e.g. a spitting spider. Depending on the species the eyesight may be well or poorly developed. Some species, such as the cave spiders, are totally blind. Depending on the species a spider's life span ranges from a couple of months to more than a decade (e.g.

mygalomorphs).

Almost all spiders have their first pair of appendages later modified into fangs with venom glands. But only a few have fangs that are large and strong enough to pierce human skin. Out of these, most cannot do any serious damage to human beings except for about four to five species which can be lethal.

The Black Widow spider, for example, which is found in South America is the most poisonous of all spiders. The female of the species, whose poison is strong enough to kill a human being, often kills and eats the male after mating and is thus aptly named the Black Widow. This spider is shiny black in colour with a red hour gla.s.s mark on the ventricle side of the abdomen. Fortunately, there are no spiders in India which can seriously harm human beings.

There are about 30,000 species of spiders in the world. They have been found upto a height of 23,000 feet up Mount Everest as well as underwater.

Almost all spiders are carnivorous. They can eat insects, small birds, mammals and reptiles, including poisonous snakes and other spiders, which they first subdue with their poison. They inject their prey with a highly lethal venom and, having no teeth, suck out the liquid from inside their prey. Large spiders with longer and powerful jaws may eat part of or even the whole of their prey. Spiders can live without food from a few weeks upto three months, depending on species, size, and age. They obtain liquid from their food and thus do not need water.

Many spiders spin webs to capture their prey. However spiders also have other means of capturing their prey. Some spiders spit a sticky web onto their prey. Others live in burrows with trapdoors. Whenever they feel hungry they come out and catch an unsuspecting insect. One species attaches a sticky drop to one end of its silken thread and holds it with its first three pairs of legs. When an insect pa.s.ses by, the spider waves the thread at the insect and ropes it in, as it were.

Some spiders sit on flowers and catch insects that come to collect nectar. Others spin a small web, hold it with their first few pairs of appendages and then throw it on insects pa.s.sing below them. Still others feed on other spiders only and are called pirate spiders. A few spiders live on the webs of other spiders: they are too small to be eaten by their host. They eat the small prey that get caught in the web, thus keeping it tidy.

Spiders also have amazing defence mechanisms. Some spiders camouflage themselves as a bird dropping. Others, as a dried yellow or black rotting leaf or twig. And yet others resemble ants which are often rejected by birds, reptiles and other insects. Some are even able to change colour and shape, to some extent, to match their surroundings.

Some species build zigzag white coloured threads in their webs which are visible to birds who avoid flying through the webs and damaging them.

The male spider is smaller than the female, and is thus liable to be eaten by his mate. So, the male uses many tactics to prevent his being devoured by his mate. In some cases the male drums or pulls at the strings of the web in a special code to announce that he is not a prey or an enemy, but a s.e.xual object.

Some spiders offer their mate a gift such as a juicy fly, wrapped in silk. But it may well be taken back after mating and offered to another female. Sometimes a male may even offer the female the empty husk of an insect. Sometimes the male loosely binds the female with silk to immobilize her before mating. Some species of male spiders may patiently wait near the web of a female spider for weeks until she has caught a prey, and then mate with her while she is busy feeding on the prey. Sometimes, the male is so small compared to the female that the female is practically unaware of him while mating and this gives him protection.

Most spiders are solitary in nature. Each one builds its own separate web. If one spider falls by mistake into another web, the bigger spider will eat the smaller spider. However, there are some spiders called social spiders that live together in one web. Sometimes there may be hundreds or even thousands of adults and young ones living in one web.

Even if a single prey is caught (such as a small fly), all the spiders will share the meal.

Spiders multiply very rapidly. After mating, an egg sac is constructed and the internally fertilized eggs laid inside the egg sac which is carried by the female with her palps and fangs. Fertilization of eggs may be internal or external depending on the species. Within 15 to 20 days, 80% of the eggs hatch. (The eggs hatch into young spiderlings.

The new born spiders are similar to their parents, only smaller. The spiderlings moult to mature.) After a gap of one week to ten days the next batch of eggs is laid in a fresh egg sac, and fertilised with the help of stored sperm. The female can do this three to four times without mating with another male, although she will readily mate with a male after the laying of every batch of eggs.

Spiders have proven themselves to be one of the best biocontrollers of insect pests. Very few of us realize that spiders were, are and will be laying traps for insects even after man has finally disappeared from the earth.

How to Rear Spiders

Spiders have cannibalistic tendencies, i.e. if two or more are kept in one container, they will prey on each other. Hence from birth, they must be separated into individual containers.

Transparent plastic containers (size depending on the individual species) can be used to rear spiders. A few pin-sized holes should be made in the lid of the container as aeration holes. One big hole should be made for dropping prey inside. It should be blocked with a piece of cotton.

Baby spiders will eat culture foods such as Thrypolium, drosophilia, fruit fly and house fly larvae. As they grow, they will eat house flies and later on c.o.c.kroaches.

Cleaning the prey remains and moults is a must. Two containers should be used. Every week the used one should be washed with soap and water, and allowed to dry in the sun.

The legs of the stands on which the spider containers are kept should be placed in bowls of water or oil to avoid ants. The adults should be fed well before allowing them to mate. Spiders will tolerate moderate room temperature.

Culturing food

1. Milk powder and a medium sized piece of cotton, mixed with water.

Every day, a teaspoon of milk powder should be added.

2. Drosophilia larvae culturing: quarter cup of wheat flour and two medium sized pieces of jaggery should be boiled in two cups of water.

Housefly and drosophilia can be reared in a wooden or metal framed box, covered with a fine mesh or netting. The above mixture should be put into small bowls and introduced into the cage. Adult houseflies and drosophilia should be captured and put inside the cage and left there to lay their eggs.

3. Thrypodium larvae: adults are found in rava and maida. A special bucket should be kept with an aeration hole and the maida or rava in the bucket, sprinkled with a little bit of water every day. A strainer can be used to strain out the larvae wherever necessary.