Worms: a nutritious, healthy snack
What makes them so important to our wildlife, and is there anything that we can do to ensure our feathered friends find their fill?
A varied feast
Worms are probably not your shopping list this week, although edible invertebrates are popular in many parts of the world, and an essential part of the diet of most birds.
Despite their unpalatable appearance, not all invertebrates are poisonous, and they are a good source of proteins, vitamins and minerals. Insects are vital for the diets of most breeding birds and their chicks in particular.
Some birds are specialist invertebrate feeders. Nightjars, swifts and house martins catch insects on the wing. All are excellent fliers, with wide gaping mouths that help them sweep up the hapless prey. Nightjars have sensitive bristles, like cats' whiskers, that help them to locate prey, and are also thought to help funnel the moths, flies and beetles into their mouths and away from their eyes.
The weather's effect on insects has a noticeable effect on the behaviour of swifts, swallows and martins. During spells of good weather they can be seen spiralling higher and higher, as they chase insects raised on thermals; they hawk low over waterbodies when water insects emerge during summer storms.
Many of our woodland and garden birds have needle-like bills that enable them to pick insects with precision. Tits and warblers search for caterpillars, flies, spiders and aphids among tree buds and leaves.
Great spotted woodpeckers favour beetle grubs in rotten wood, and have chisel-like beaks and long, barbed tongues perfect for the job. Green woodpeckers are particularly fond of ants, and are often to be seen foraging for their nests among short grass.
Song thrushes, robins and blackbirds feed on the ground, and for them there simply isn't anything as delicious as a worm. All have strong bills that enable them to pull struggling earthworms from the soil, and large eyes that help them to see in the early morning light, when earthworms are most active near the surface.
Song thrushes turn their attention to snails when they can't get worms, but removing a snail from its shell takes a lot of effort and time. Song thrushes are well-known for using hard stones as 'anvils' to break open the shells; blackbirds are well-known for stealing the snail from the song thrush, once it has done all the work!
Long-billed waders like curlews, godwits and snipe find their invertebrate food by feeling through soft mud with their sensitive and sometimes flexible bills. Each has a different technique, which you will see if you watch them swiping, stabbing or needling at the ground.
There are few specialist insect feeders that can survive our northern winters, as food becomes too scarce for them. Most migrate south to return in the spring when the weather grows warmer, days become longer, and insects are more abundant. Though they may feed predominantly on invertebrates in the summer, most resident birds gradually switch to fruit or seeds during the autumn.
The decline in many once-common birds has been linked to their reliance on invertebrates. Less invertebrates means that chicks go hungry, or fail to survive after leaving the nest. Insecticides reduce the numbers of insects in the environment, and toxins can build up inside the bodies of birds that feed on them. Slug pellets are also a problem, as the poisons become concentrated in birds and animals that feed on slugs and snails, like song thrushes and hedgehogs.
Climate change is also affecting the numbers and types of invertebrates available to birds. In hot weather, earthworms, snails and slugs can become scarce, and warmer springs mean that caterpillars mature more quickly, so they are not available when birds like pied flycatchers need them for feeding their young.
Garden bird buffet
By making your garden better for invertebrates you can give your garden birds a better chance to find food and raise their chicks. By avoiding the use of insecticides and slug pellets, you will protect garden birds, and supply them with an abundant, safe source of food: after a while, birds and predatory insects will keep pests at bay.
Planting native shrubs and trees helps – willow, oak and birch support lots of caterpillar species to feed hungry tits and warblers. Grow annuals and perennials that attract nectar-feeding insects.
A little untidiness helps: log-piles, decaying leaves, and longer grass are all good habitats for insects, and if your garden has more invertebrates, you should see more birds. Insects can be interesting and beautiful, too!
How you can help
Who's living in your garden? Make your garden wildlife-friendly.