Spiders are not insects, they are arachnids, a family that includes harvestmen, ticks, mites and scorpions.
Three arachnids: harvestman, tick and scorpion
The difference between spiders and insects is most easily defined in numbers: spiders have only two parts to their bodies not three, they have eight legs not six, six or eight eyes while insects have only two, and all spiders have up to six silk-producing spinnerets whereas most insects have none at all.
Insect anatomy compared to a spider’s anatomy
Here are five more spider numbers, just to keep you interested.
SIX: the number of species of the genus Tegenaria that live in our houses in the UK, all of which we are inclined to call house spiders. They range in size from the relatively small Tegenaria domestica to the quite large Tegenaria parietina, which can reach a leg span of 120mm (5 inches) in the adult male.
FIVE AND A HALF MILLION: the number of spiders that a recent study found per hectare in an undisturbed grass field in Sussex.
Some pf the 5.5 million spiders in an hectare of undisturbed grassland
TWENTY: the length in meters of the silk thread a garden spider (Araneus diadematus) produces overnight to mend its web.
FIVE: the number of times that spider silk is stronger than steel.
FORTY FIVE THOUSAND: the number of species of spider in the world, found in all possible habitats in every country except Antarctica.
Southwick Country Park Nature Reserve 
In recent years I have noticed a marked reduction in the number of spiders found in my home. Now I do all I can to protect and nurture any that I find, even the big house spiders that make my flesh creep! So I have a glass and piece of card ready to catch and move big spiders to a safer place in the house where I can’t see them!
Well done Barbara! I am too scared of big house spiders to get close enough to catch them. Instead I cultivate cellar spiders (Pholcus phalangioides – see below), the slow and wobbly sort that hang out in untidy webs in the corners of your rooms; they will trap and eat house spiders and the house spiders know it and stay away.
