The Importance of Hedgerows for Butterflies - Hedgerow Week 2022

There are 35 species of butterflies in Ireland - 23 of these breed on hedges. Over-management of hedges removes butterfly eggs, larvae and nectar sources for adult butterflies. Catherine Keena, Teagasc Countryside Management Specialist and Jesmond Harding, Butterfly Conservation Ireland explain

Main photo above: Small Copper butterfly on gorse. (Photo: Jesmond Harding)

Leaving around one third of a hedgerow uncut each year helps butterflies, moths and many other wildlife groups. However, some three-year-old hedges are too strong for a flail to cut without causing damage so where hedges are trimmed annually, it is essential to leave some escaped hedges on the farm. 

Escaped or untopped hedges or treelines which have never been topped provide great habitat for butterflies and moths, as do the occasional individual trees allowed to mature within topped hedges. Fenced field margins alongside hedges containing native grasses and flowers increase their biodiversity value significantly, of critical importance in intensive agriculture. Results from a study of the abundance of moth species showed that really good hedgerows containing trees with fenced field margins, mitigated the impact of intensive arable farming. 

Hedge species - value for butterflies

The value of a hedge depends on its composition. Whitethorn is of high value – even a monoculture whitethorn hedge as it supports 62 species of larger Irish moths along with the additional wildflowers at the base on which moths feed at night, as well as other species that feed on developing berries. Willow is really good for biodiversity, flowering early in spring. Brimstone butterflies, Peacocks, Comma and Small Tortoiseshells waking up from a long winter hibernation parched for nectar, head straight to willow. An amazing 115 of our larger moth species breed on willow, making it the single most important plant for moth species and that just counts the larger moths, there are hundreds of micro moths which are much smaller and a lot of those breed on willow too. Birch supports 102 moth species. Oak supports 72 species of larger moths and more micro moths which are the tinier ones and the purple hair streak butterfly. Oak trees within hedges provide the same support as an oak woodland, even in exposed locations. Beech isn’t native and supports less insect because it hasn’t developed alongside the native fauna of Ireland. There are only 22 species of moth that breed on beech. While fuchsia does provide nectar both it and montbretia which are often found in Cork and Kerry hedges, are not native and are very invasive, encroaching on and eliminating native plants such as Bush Vetch, Tufted Vetch and Common Bird's-foot-trefoil. 

The herb layer at the base of hedges containing plants such as Cow Parsley and Greater Stitchwort are brilliant areas when sunny in spring for butterfly and moth species. Insects are cold-blooded so they need external heat from the sun to warm themselves up so those sunny spots are really brilliant for butterfly and moth species. There are some butterflies, like the Speckled Wood that will have more than one generation a year. In spring when it's cooler, the Speckled Wood lays her eggs in the sunny side of a hedge but summer when it's warmer they actually lay their eggs on the shaded side of the hedge so the eggs don't desiccate and dry out or the larvae don't dry out so a shaded part or side of a hedge is also very good. Some moths eat decomposing mouldy leaves and there are also larvae that over-winter inside leaves in in the curl of a dead leaf. Hedge banks are great because and are lower in nutrients, which allow different plants that can't tolerate high nutrient levels to grow such as Lady’s Bedstraw - a yellow frothy flower with a beautiful scent which was used to fragrance ladies’ beds. Patches of scrub are incredibly important for butterflies, especially in unshaded areas with native flora and grasses. 

Butterfly life cycle

Female butterflies lay eggs in or near a foodplant in the best location for the larva which develop from the eggs. Most Irish butterflies overwinter in the larval stage. Larvae are either a similar colour to blend in with their foodplants or a completely different colour to warn predators that they are harmful. Larvae moult and shed their skin several times, before becoming a pupa. This is the stage when the adult butterfly develops inside. Pupae are usually deep in vegetation and blend in with their surroundings. Adult butterflies push their way out of the pupal skin and fly away after drying their wings. In Ireland butterflies are mainly on the wing from April to September. 

While some butterflies, like the Orange-tip and Green-veined White butterflies can use a range of plant species for their young, several butterflies are fully or mainly dependent on one plant for their caterpillars. The Brown Hairstreak butterfly relies totally on Common Blackthorn. The Small Tortoiseshell and Peacock breed exclusively on Stinging Nettles. The Brimstone butterfly breeds on two small trees only - Alder Buckthorn and Purging Buckthorn.

Here are some butterflies and moths that depend on hedgerows and extended field margins.

Left to Right: Brown Hairstreak butterfly and its caterpillar feeding on delicate new blackthorn leaves in spring after hatching from eggs which have overwintered on the plant. This butterfly is only found in certain small pockets in areas in the Burren in County Clare and Galway and around Lough Corrib in County Galway and Mayo. It relies strongly on lightly managed hedgerows and hedgerows cut on a long rotation. (Photos: Jesmond Harding)

Left to Right: Emperor moth egg cluster on Alder Buckthorn and the adult female moth. (Photos: Jesmond Harding)

Left to Right:  Sulphur yellow Brimstone butterfly and its green caterpillar on Alder Buckthorn. (Photos: Jesmond Harding)

Holly Blue butterfly appropriately perched on Common Holly. (Photo: Jesmond Harding) Holly Blue butterflies breed on holly and the later generation of the year breed on ivy laying their eggs from August to October. The caterpillars feed on the little ivy berries.

Left to Right: Hedge brown or Gatekeeper butterfly breeds on grasses that grow at the edge of the hedge and Orange-tip butterfly taking nectar on greater stitchwort in a hedge in springtime. (Photos: Jesmond Harding)

Left to Right: Red admiral perched on whitethorn and Green Hairstreak on Wild Raspberry at the edge of a hedge in north Kildare. (Photos: Jesmond Harding)

Left to Right: The Beautiful Carpet moth feeds on bramble, raspberry and hazel and the Barred Yellow moth feeds on Common Dog-rose. (Photos: Jesmond Harding)

Further Information

For more information on butterflies: https://butterflyconservation.ie/wp/

Join Butterfly Conservation Ireland at https://butterflyconservation.ie/wp/join-us/

See Jesmond Harding’s new book – The Irish Butterfly Book 

The Irish Butterfly Book published in December 2021 by Jesmond Harding 

Hedgerow Week 2022

Friday August 26th to Friday September 2nd marks Hedgerow Week 2022.
The theme for the week is Best Practice Hedge Cutting
Get more information on hedgerow week 2022 here
Get more information on hedges here