Friday, February 24, 2012


Almost all spiders possess venom, which may inject into their prey through sharp, hollow fangs. Few spiders are able to pierce human skin, but about 30 species out of a total of about 40,000 can cause severe illness or even death if they bite people. However, spiders are not usually aggressive and have rarely been drawn to bite unless it is provoked. The very notorious spider is undoubtedly America’s Black widow. Although its fangs are very short, it manages to get them through the skin to inject venom which is volume for volume, about 15 times more poisonous than rattle snake venom. The spider obviously injects a much smaller amount than a rattle snake but it causes severe pain and nausea, and has resulted in many deaths over the centuries. The closely related red widow in habits the sand pine scrub of southeast Florida. Similar spiders are found in southern Europe as well as in most other warm areas of the world.

The brown recluse spider from the southern USA injects venom that destroys blood and other tissues. It has caused some deaths. The Sydney funnel web is Australia’s deadliest spider, and is particularly dangerous because it often makes its home in gardens. The most deadly South American spider is the wandering spider an aggressive hunter that has been known to kill children. It occasionally turns up elsewhere, having travelled in crates of bananas. Its fangs are over 400 long but the longest fangs –up to 12mm long- belong to the bird eating spiders or tarantulas. Luckily, these big spiders do not have particularly strong venoms. Antivenins are now available to treat victims of most of the dangerous spiders. Provided they are given quickly they should result in almost immediate recovery.

Sunday, February 19, 2012

Insect produce

Insects provide us with a surprising number of commercially important materials. Cochineal, which is widely employed as a red food dye, and shellac, used in varnishes and polishes, are both obtained from scale insects. The honey bee supplies us not only with honey but also with bee wax for polishes. Silk, most of which is produced by the silk moth bombyx mori in a process that was for centuries a closely guarded Chinese secret, is one of the finest natural fibers in existence, and has long been valued for fine clothes because of its shiny appearance and light weight.
Natural pesticides
The role of ladybirds in controlling aphids is well known, but there are many other pest killing insects. Gardeners can now control whiteflies and other greenhouse pests by buying a supply of minute parasitic insects that attack and kill the pests. The big advantage of these biological control agents is that they leave no harmful residues on the crops. Insects can also be used to control weeds. For example, the larvae of a South American moth called cactoblastis successfully rid Australia of the introduced prickly pear cactus.
Insects as human food
Locusts have always been eaten in Africa and other warm areas. Fried in butter after removal of their wings and legs, they are said to be very tasty and nutritious. Honey pot ants, which are full of stored honey, are eaten by many desert dwellers. Witchetty grubs, eagerly sought by Australian aborigines, are wood boring caterpillars. Many beetle grubs, including the mealworms often used to feed birds and other pets, are also widely enjoyed by indigenous peoples, among whom they are considered highly desirable food, especially when fried.