After months of gloom about the environment and Britain's embattled wildlife, reassurance may be on its way from a creepy and often-unloved source.

Scientists and conservationists are optimistic that an annual survey will record a bumper crop of the country's spiders – more than 650 species which variously weave, jump, hunt and have up to six eyes.

Anecdotal reports of high numbers of spiders, from amateur enthusiasts as well as specialists, are already piling up at the campaigning charity Buglife and the British Arachnological Society (BAS). Temperate weather since the end of winter, with few very hot or cold spells, has suited the animals, which emerge at this time of the year to mate.

Monitors also expect an increase in the number of craneflies, or daddy-longlegs, which like the spiders are significant indicators of the ecosystem's wider health. Buglife, whose motto is "conserving the small things that run the world", said that a rise in arachnid numbers would benefit not just spiders but their many predators.

It also has implications for good housekeeping. "One house spider will catch and dispose of 20 or so flies for you," said Matt Shardlow, director of Buglife.

The survey is partly designed to end the instinctive "zap it" reaction of many people confronted with a spider or a web. It is hoped that as well as recording numbers, the exercise will increase understanding of species that still have much to teach humankind.

"If you don't like them, just leave them alone and they will leave you alone," said John Partridge, secretary of BAS. "But if you can, get up close and have a look at how beautifully coloured they are."In between commandeering friends' gardens today for TV photo opportunities for spiders, Shardlow said "lots of fantastic spiders" were around at the moment.

The six types of house spider, which can grow to a legspan of a couple of inches, are familiar. Others include the jumping zebra spider, which leaps on to its prey rather than bothering to make a web, and the pink prowler, which has six eyes.

"If you move furniture around and look underneath, or poke about in the garden, you should make some good finds," Shardlow said. "But we're particularly interested in numbers overall. The BAS spider recording scheme does a very good job of marking where particular species have been found, but we need a lot more data on how many spiders of all kinds there are.

"We know that numbers have fluctuated in recent years, and almost certainly went down badly in 2007, which was one of the worst years in living memory for butterflies and moths, which are much more widely recorded. Recent cold and wet summers have been bad news for all bugs."

The survey was welcomed by the Royal Society for the Protection of Birds, which sees the spider population from the point of view of food. Ian Dawson of the RSPB said: "It's debatable whether some of our resident insect-eating birds, like the wren, would be able to survive the winter without a plentiful supply of spiders in leaf litter and under shrubbery. Let's hope the suggestion of an increase is correct."

Cranefly larvae also have a role in maintaining soil health and breaking down leaf litter and compost.

"They are very important for biodiversity, without which we would not last very long, Shardlow said. "And if it weren't for spiders, we would be overrun with flies and other pests which make our life unbearable."

Handling spiders is not recommended, partly because they probably do not enjoy it, but no one has died in Britain from the small number of bites needing treatment - about 10 a year - recorded by the Natural History Museum in London.

Dangerously venomous foreign species are occasionally found in imported fruit, usually at the docks or wholesale markets.

A deadly Black Widow is now in Bristol zoo after arriving in a hosepipe brought back from San Francisco by a family from Newport, South Wales in June.

Most spider-related injuries stem from arachnophobia. A German woman who lost a £5,200 compensation case for a broken wrist in July. She panicked after seeing a large but harmless spider, and fell over.