What would you think about if I asked you for good foodplants for butterflies and moths? Buddleja? Verbena bonariensis? Hebe?
It’s true – they’re all great nectaring plants, and non-native to the UK. So why should I bother with native plants if I want to encourage butterflies and moths?
Well, many native plants are very good sources of nectar, of course. Hemp agrimony, knapweed, honeysuckle, wild marjoram and field scabious spring immediately to mind. These are all attractive and in some cases long flowering wildflowers. As nectar plants are they as good as the ornamentals? It’s a far from straightforward question and not my topic here!
Where native plants incontrovertibly DO win is as foodplants for caterpillars. British caterpillars, by and large, need British plants to munch. This can, of course, extend to cultivars, which explains why cabbages are regularly written off. There are exceptions too; I offer up nasturtiums (from South America) in my veg patch as a sacrifice to happy Small White caterpillars.*
At this point gardeners say they have a nettle patch for caterpillars. Well yes – good foodplant but not enough on their own. Atropos Publishing has a good guide which shows which species of butterfly and larger moth depend on which foodplant. Urtica – nettles – have 35 associated caterpillars. It highlights the difference between imported plants and native. Buddleja are a good example; the book lists only 3. This is very different to a native plant – field scabious has 14.
Grasses too are good larval foodplants, which is one of the reasons why we encourage people to sow meadow mixes rather than just wildflowers. Cocksfoot, for example (although not ideal for a meadow), comes in as supporting 35 different types of caterpillar.
Trees and hedge species are even better. Sometimes they have almost exclusive or totally exclusive relationships with individual plants. I think of Yellow Brimstones and Buckthorn, Purple Emperors and Oak, Brown Hairstreak and Blackthorn. The king of all our plants is the Oak; according to the book, both oaks support over 120 types of moth and butterfly caterpillars. It’s said an oak tree will lose around half its leaves to insects in an average year.
Which are the top five foodplants? They’re all native trees or shrubs:
English and Sessile oaks (Q. robur and petraea)
Willows (Salix spp.)
Birches (Betula spp.)
Hawthorn (Crataegus spp.)
Blackthorn (Prunus spinosa)
*and thence happy blue tits etc.etc.