It's all too easy to think of insects as friends or foes: bees are good, wasps bad; butterflies are good, flies bad. You admire bumblebees and point the insecticide can at wasps. As National Insect Week starts on Monday, now's a good time to explore what insects do in the garden, why they're important to gardeners and how we can learn more about them.

Insects go through three stages as they grow: they start life as eggs, develop into larvae and finally become adult insects. Many of them spend most of their lives as larvae, underground, in trees, leaves and, of course, in fruit, passing little time as the fetching butterflies or moths you enjoy in the garden. The most extreme example are the mayflies, whose Latin name – ephemeroptera – more than hints at their short lifespan. Other species live for a few short hours with scarcely enough time to lay eggs, never mind feed.

You'll catch a glimpse of dragonflies and damselflies while they're hurriedly laying eggs on pond plants such as irises and rushes. The resulting larvae spend a year under water but these carnivores consume other tiny creatures and keep the pond healthy; they have no interest in your plants.

Many insects help control creatures we consider to be pests. Several of the 350 British species of ground beetles eat slug eggs and small slugs. Lacewing and hoverfly larvae consume greenfly for us, leaving a tiny, fairly harmless population. That's why I'm not even aware of these sap suckers in my garden. The dreaded wasps also do a sterling job here by carting off these protein-rich pests to their bykes. They only become a pest when larvae in the nest have grown up and the workers get their P45s and turn to consuming sweet fruit.

For all my love of nature, I draw the line when I see a queen wasp starting to set up home in the potting shed and confess to having squashed one on my bedroom window this morning. Sleepy wasps on the pillow in autumn don't appeal.

Of course, some larvae, such as those of carrot root fly and cabbage butterfly, are a perfect nuisance to gardeners. We should use protective barriers for these crops and let their predators play their part in the garden's complex ecosystem, well away from our plants.

Undoubtedly, though, pollination is the most important service insects provide. What can beat the wonderful sound and sight of bumblebees in the flower garden? And we shouldn't forget that, in their different ways, insects all play their part.

The more closely you observe these insects at work, the more fascinating the circus becomes. Which flower colours and shapes attract which insects? How many species of bumblebee can you see and identify in the garden?

To help answer these and many other questions, Monday sees the launch of Blooms for Bees, a citizen science project in which gardeners from across the UK are asked to provide the research data scientists can then use.

There's an app to help identify different bumblebee species, and gardeners are being asked to send photos of bumblebees in their gardens, which will help the organisers identify which bumblebees visit which plants. This data can then be used by the sponsors, Garden Organic and the Royal Horticultural Society, to help horticulturists develop garden plants, especially bedding plants, that are bee-friendly. Blooms for Bees is part of National Insect Week. Visit nationalinsectweek.co.uk