There are 26,000 million insects living in every square mile of habitable land on Earth.
About 35,000 species of spiders are known and more are being discovered every day.
The web of an average garden spider contains up to 30 metres (nearly 100 feet) of silk.
In an old field in South Wales, researchers recently found approximately one million spiders per acre (2.5 million per hectare).
Insects have a much greater impact on the planet than vertebrates.
In tropical forests, insects eat 12 to 15 per cent of the total leaf area as compared to only two to three per cent eaten by vertebrate herbivores.
Insects eat 15 to 20 per cent of all crops grown for human consumption and, locally, the damage may be much higher.
Leaf-cutter ant colonies of many millions can excavate room-sized underground chambers in which they cultivate fungus gardens.
The world's largest spider is the goliath bird-eating spider with a body length of 3.5 inches, a leg span of 11 inches, fangs measuring one inch long and a total weight of 4.3oz.
The biggest spider webs in the world are made by species in the Tropics and measure well over one metre in diameter.
The largest beetle is now known to be the Titan beetle from the Amazon Basin. It is up to seven inches (170mm) long and will appear in the series for the first time on television.
The rain forests of Central and South America are home to the biggest centipedes. Some have been recorded at around 300mm and more, and the African Savannah holds the record for the biggest millipedes at about 280mm.
Millions of years ago, anthropods were a lot bigger than they are today.
There were millipedes more than one metre long and giant spiders weighing more than one kilogram with leg spans of up to 500mm.
Carboniferous period dragonflies whirred though the air on wings that were 760mm across. These creatures got smaller and smaller when efficient predators such as the reptiles evolved.
The smallest insect is the fairy wasp with a length of only 0.2mm but it flies underwater, as the series will show. The wings of these tiny insects are simple hair-fringed struts.
Termites invented air conditioning for their mounds millions of years ago. Life In The Undergrowth goes inside a mound to see how it works.
Although individually small, termites' total biomass per unit area is double that of the biggest herds of African hoofed grazing animals.
Dragonflies are the fastest insect fliers in the world, attaining speeds of up to 36mph – no wonder they were so difficult to film!
Invertebrates were the first farmers on Earth. Termites tend fungus gardens, leaf cutter ants make underground compost heaps and many species of other ants tend and protect aphids for their honeydew.
A swarm of desert locusts may consist of up to 50 billion individuals.
As each can eat its own weight of food in a day, the whole swarm eats somewhere between 75-100,000 tonnes (about four times as much food in a day as would be consumed by the human population of New York or Greater London).
Today, there are about 20,000 species of bee.
Wood ant queens can live as long as ten years.
It is estimated that, every year, the world's formicine ants release one million tonnes of formic acid into the atmosphere.
Purple Crow butterflies migrate up to 500 miles each year.
The velvet worm can squirt glue, just like Spiderman.
Fossil evidence suggests that cockroaches inhabited Earth around 300 million years ago. The species around today have changed little since those early days.
Snow scorpions are superbly adapted for life in cold conditions. These insects contain antifreeze compounds and can tolerate temperatures up to six degrees below freezing. They will die if held in the human hand.
A 500g jar of honey represents about ten million trips from the hive to flowers and back again.