Friday 08 January 1999
The smallest spider is the Mygalomorph spider from Borneo, whose body measures just 0.5mm long - the size of a coffee granule. The largest is the goliath bird-eating spider, the largest of which has a leg span of 29cm (11in) - the length of your forearm.
Q: How long do spiders live?
Ordinary spiders live for about a year, although up to five to six months of this may be spent in the egg stage. However, some South American tarantulas can live for as long as 20 years, while some tropical jumping spiders only live for three months.
Q: How is snake venom produced?
Venom is produced at the back of the snake's head (behind the eyes). Glands similar to those that produce our saliva make and store a cocktail of venoms, toxins and enzymes, which travel through ducts to either fangs or groves in the teeth. The venoms work in different ways: they can paralyse prey (cobra venom affects the nervous system) or digest tissues and organs (rattle snakes) which helps them in their food intake.
Q: Is there such a thing as a bionic eye?
People may be either blind from birth or have lost their sight through disease or an accident. For those born blind, an artificial eye may not be all that useful as their visual cortex has not been trained to see. For those that have lost their vision later on in life, a bionic eye (an implant that replaces damaged retinal cells) may restore some of their sight.
Retinal implants are constructed from 25 electrodes just a thousandth of a millimetre thick, and incorporate a miniature solar panel. When the panels absorb light, tiny currents are generated in the implants which then stimulate the ganglion cells beneath, bypassing damaged retinal cells.
So far, the implants have worked in animals and in one human volunteer who had gone blind through glaucoma. The patient could see a light shone in the eye, and make out simple letters. If more electrodes are used, the wearer's vision might be even better. Next, the researchers will need to make an implant that does not corrode in the salty solutions of the eye, and will not slice into the retina (the implants are razor sharp as they are so thin). Researchers remain hopeful that eventually such implants may restore sight to some blind people.
Q: Why do your eyebrows grow as you get older?
The continued growth of hair in men is thought to be due to the male sex hormones (androgens). Hair in different parts of the body varies in its sensitivity to androgens and eyebrows, nose, ear and patches on the top of the shoulder respond to continual high levels of the hormones. It therefore does not usually appear in women, who have much lower levels of androgens. Why evolution should have produced them is unclear. There is, however, a hint from some species that females seek out males who are older because that shows they are good at surviving and so must have a fit set of genes. The males of these species develop outward signs of their age. Perhaps going grey and sprouting ear and nose hairs was once attractive to women and so men showing them were successful at getting their genes into the next generation.
You can also visit the technoquest World Wide Web site at http://www.sciencenet.org.uk
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