We are about to move for a while from the main Caterpillar Foodplant theme of our website to discuss Nectar Plants, but we won’t of course be losing sight of the fact that without caterpillar foodplants there won’t be any adult butterflies to drink the nectar.
Limited Caterpillar Foodplant Choices As we have seen, butterflies are highly selective in their choice of leaves on which to lay their eggs, due to the need to provide a high quality, nutritious diet for their caterpillars - which usually means fresh, young leaves in a warm, sheltered spot. The leaves also need to provide camouflage, and in many cases toxic chemicals that the caterpillars can safely concentrate within their bodies to make themselves unpalatable to birds and other predators. In these days of shrinking habitats, finding the right plant in the right place becomes more and more difficult.
But Wide Nectar Choices In contrast, when it comes to what flowers they get their own nectar from, butterflies are far less selective. But they do have preferences, and to attract as many types of butterfly to your green space or garden as possible, the wider the range of nectar plants the better. Most commercial seed mixes contain twenty or so. They are typically selected by the suppliers to provide nectar over as long a season as possible, from when the first butterflies emerge from hibernation in spring right through to when the second or third brood are on the wing as autumn approaches. They also include species with long-tubed flowers for those bees, butterflies and moths that have a long proboscis.
Wildflower Mixes for Every Occasion Most good commercial suppliers have mixes geared for specific types of terrain. Scotia seeds for example have an especially intriguing selection including a Dry Meadow Mix, Wet Meadow Mix, Flowering Lawn Mix, Hedgerow Meadow Mix, Northern Haymeadow Mix, Highland Grassland Mix, Coastal Meadow Mix, Urban Pollinator Meadow Mix, Green Roof Mix, Bee, Bird and Butterfly Mix, Coastal Dry Places Wildflower Mix, Flowering Lawn Wildflower Mix, get Nectar-rich Quick Mix, Haymeadow Wildflower Mix, Hedgerow Wildflower Mix, Pond-edge Wildflower Mix, Wetland Wildflower Mix and a Woodland Wildflower Mix. With most of the hard work having already been done for us by the seed companies, it’s just a case of deciding which mix best fits our location, and if we have special favorites or extra caterpillar foodplants, adding them to it. Some wildflowers are tolerant of a wide range of conditions and appear in most mixes, while others are far more dependent on specific conditions of wet or dry, chalk or acid soils and so on..
A Word of caution. There are some wildflower mixes on the UK market which turn out to include the wildflowers of America, South Africa and elsewhere. They may produce just as much nectar and pollen as British wildflowers but our insects have not evolved to use them as larval food plants, so avoid them. Always make sure that you only choose companies like Scotia Seeds, Emmorsgate and others that either grow their own stock in the UK or source it from growers who do. Most of our wildflowers also grow on mainland Europe, but to keep your stock pure, whatever country you live in, buy as locally as possible.
Pollen or Nectar? Should we choose those wildflowers that produce most pollen, most nectar, or both? Our native butterflies don’t eat pollen – bees do, but not butterflies - so if our main aim is to attract butterflies to come and set up breeding colonies, the amount of pollen produced by the wildflowers is irrelevant. It’s their yield of nectar that will be of more interest to us.
If our aim were to provide wildflowers for a colony of honeybees it would obviously be a different matter. It's important not to confuse the life style and diet of bees with that of other insects. Bees are extremely unusual insects for at least two reasons. Firstly their larvae are cared for and fed by the adults. A few other kinds of social insect including ants and termites and a few species of wasp adopt a similar strategy, but the vast majority of insects, including butterflies and moths, after carefully choosing a relatively safe place to lay their eggs, leave their larvae to fend for themselves. Secondly, bees feed themselves and their young exclusively on nectar and pollen. Butterfly caterpillars eat leaves and buds, not pollen and nectar. Even the adults (with some specialised tropical exceptions) only drink nectar, and do not avail themselves of the flower's pollen, although they might get contaminated by it and carry it to the next flower they visit, inadvertently fertilising it.
High Yielders A detailed study has recently been carried out of the nectar yield of a wide range of wild flowers native to Britain and Ireland. The figures in brackets are the average micrograms, to the nearest hundred, of nectar sugar produced per day by a single flower or, in the case of members of the daisy family, by the whole flower head. By far the highest yielding flowers were those of Ragwort (2900), Creeping Thistle (2600), Spear Thistle (2300), Dandelion (2100) and Cat’s Ear (1800), none of which usually appear in wildflower mixes. These were followed by the Rough Hawkbit (1800), Common Knapweed (1500), Scentless Mayweed (1400), Corn Marigold (900), Cornflower (900), Viper’s Bugloss (700), Corn Marigold, sow thistles (600), and Autumn Hawkbit (500), Musk Mallow (500) and Oxeye Daisy (500).
As a general rule, the highest yielding flowers were those of the daisy family the Asteracea, which have composite flower heads. In other words the flower does not consist of a single flower as in poppies but has large numbers of tiny florets each producing nectar. Not every wildflower was studied so it is likely that for instance other types of thistle produce a similar yield of nectar to the Spear and Creeping Thistle.
But that doesn't mean they are the only ones of value. A lot of other wildflowers like Bird’s-foot Trefoil (60) and Wild Red Clover produce comparatively small amounts of nectar per flower (50) but they produce an abundance of flowers, often blanket a wide area, and are flowering over a long season, so it all adds up.
Many seed mixes like Scotia’s get-Nectar Rich Quick Mix omit the highest yielders, the thistles and ragworts, but compensate for this by including many of the other less controversial high yielders. There is of course no reason why you should not welcome thistles and ragwort to your own green space and garden. They fact that they are the highest nectar yielders, the major food plants of caterpillars of the Painted Lady butterfly and day-flying Cinnabar moth respectively, as well as producing extremely attractive flowers, make them good choices for any wildflower garden.
Poppies interestingly produced less that 1 microgram of nectar per day but compensated for this with their huge output of pollen for bees.
The Butterflies Choice? The very high nectar-yielding wild flowers are attractive to many species of butterfly. In one study, about ten of our butterflies were most often seen feeding from thistles. But not all. Butterflies that spend most of their lives in more specialised environments may focus on the nectar in flowers that grow in those environments. For instance, those that live in colonies in woodland glades like the Orange-tip, are more likely to be seen feeding from Bluebells, brambles, Bugle, Cuckooflower, Dandelion, hawkweeds, or Ragged Robin than from knapweeds, Ragwort and thistles that tend to grow in more open locations. The Wood White and the Cryptic Wood White seemed to have a strong preference for the nectar of Bird’s-foot Trefoil; the Heath Fritillary and Silver-washed Fritillary for bramble nectar: while the Pearl-bordered Fritillary and Small Pearl-bordered Fritillary were especially keen on Bugle nectar
.Sometimes a butterfly has no choice but has to make do with the nectar plants that are there. The common daisy only produces about 50 micrograms per day of nectar sugar, but it’s out there on the lawn early in the year when there might not be much else available in the area for insects emerging early from hibernation.
The Length of the Proboscis While there are those wildflowers that produce more nectar than others, and produce it over a longer period, the shape of the florets is also important. In butterflies like the Speckled Wood and Gatekeeper, the proboscis is not long enough to reach nectar at the base of long-tube florets like those of buddleja, on which the larger, longer-tongued Peacocks and Small Tortoiseshells so readily feed. Butterflies with a shorter proboscis need flatter flowers like those of Ragwort and other members of the daisy family. Most butterflies, bees and other pollinators can extract nectar from these regardless of the size of their proboscises. But that means lots of competition, so those butterflies that have evolved a long proboscis are more likely to be seen dining at the more select restaurants accessible only to those that can reach the nectar in their deep-tubed florets.
Conserve Existing Nectar Plants The odds are that unless you suffer from a bad case of block paving, you will have some valuable nectar plants in your green space or garden already. Don’t overlook them. Because they are so common, bramble flowers are one of the most important sources of nectar for butterflies over the country as a whole. If you don’t have wild bramble in your garden at the moment and don’t want to plant it, go for some of the higher yielding commercial blackberry and raspberry varieties, so that while providing them with nectar you can take advantage of the butterflies’ pollinating services to provide you with juicy fruit. There are even ‘thornless’ varieties, though it might be argued that these provide less protection to invertebrates from collateral damage due to herbivores.
Ready sources of nectar are important for butterflies and bees emerging in early spring, so early flowering plants like native bluebells and primroses are always worth encouraging
It may be hard to believe, looking at the restrained, closely clipped hedges that surround so many front gardens, that privet flowers are a great source of nectar. But it has to be allowed to flower, so give at least part of your privet hedge free reign, cut down on the cutting and allow at least the garden side of part of it to produce flowers for the butterflies. Dandelions too are an excellent source of nectar, one of the highest yielders of all, so avoid the temptation to pull these up from between the paving slabs. Pull up the paving slabs instead! Dandelion lookalikes like Cat’s-ear and the hawkbits are similarly high nectar yielders.
Thistles of all varieties with their beautiful flowers, extremely high levels of nectar, and wealth of associated insects should be welcome in any garden, especially Scottish ones. It is the Emblem of Scotland after all! It could become an emblem of Scottish biodiversity. Okay they are prickly but so is holly, and exotics like pyrancantha produce not just prickles but real stem-derived stabbing thorns, but this rarely seems to act as a deterrent to growing them.
Not all Sources of Nectar are Wild Flowers As well as privet hedges, any fruit trees you have growing in your garden will be especially valuable as they are likely to provide an early source of nectar. Wild plums trees are particularly good. Blackthorn is another wild tree that produces a profusion of blossom early in the year. Later in the year any tree that is insect pollinated will provide nectar and pollen for insects.
Natives Versus Exotics Firstly in praise of native wild flowers I mentioned buddleja as a nectar source for our long-tongued Small-Tortoiseshell. But should we be growing invasive aliens like this? In contrast to native wild flowers, it is often the case with exotics that none of our native insects have evolved to eat them. With so few insects to keep them in check, some exotics, if they adapt to our climate, can get out of hand. Buddlejas despite their merits, are an obvious example. In many parts of the country they are choking out our native species, a situation especially noticeable along large stretches of railway line where they predominate to the exclusion of a wider variety of native hedgerow plants that were there previously. The nectar they provide may be good for long-tonged bumble bees and adult butterflies but they fail to provide the all-important food for butterfly larvae and the larvae of other species.
Despite the reservations, if you already have good nectar sources like buddleja, Verbena and other exotics growing in your garden they are worth keeping. The spectacle of the flower heads of Sedum spectabulae covered with Small Tortoiseshells is worth hanging on to. Non-invasive exotics like Sedum may be useful for supplementing nectar levels at times and in areas where there are currently not enough wildflowers to supply the demand, Starting from scratch though it is much better to go for native plants rather than potentially invasive exotic ones. The aim should always be to build up the numbers of nectar-producing wildflowers so that exotics are not needed.
This is because any species of wild flower will be the larval foodplant, if not of butterflies, then of other types of insect. Not all of the native plants in your green space or garden even need to provide pretty flowers. Why should they, when the less flamboyant species are likely to support equally important populations of invertebrates, and are just as good for biodiversity. Many people with less concern for the environment are content with blocks of concrete, so I’m sure we can welcome a few flowerless leafy wildflowers in our garden.
Not All Butterflies Drink Nectar It is easy to imagine that all adult butterflies and moths fuel their flight by drinking nectar, but this is far from being the case. Many species of butterfly spend their lives in woodland feeding on sap and aphid honeydew, and rarely if even touch the sugary nectar offered by flowers. These include the Black Hairstreak, Brown Hairstreak, Large Blue, Large Tortoiseshell, Purple Emperor, Purple Hairstreak, White Admiral and the White-letter Hairstreak, all fairly rare species confined to deciduous woodland in southern England. But there is one much more common and widespread butterfly, the Speckled Wood, familiar in wooded areas in England that specialises in honeydew for most of the summer, only turning to flowers like bramble and Ragwork early and late in the season when there are less aphids around. Some of our most common nectar-feeding butterflies like the Peacock, Red Admiral, Green Hairstreak, and Holly Blue will also take honeydew along with their nectar.
Butterflies that feed primarily on honeydew typically like the Speckled Wood typicaly have shorter tongues than those that feed on nectar. This means that when they do turn to flowers, those that produce their nectar at the bottom of deep florets are inaccessible to them, and they are often seen feeding on the flatter florets of Ragwort and Wild Privet. In British species the average length of the proboscis is about two thirds of the body length. Longer proboscises have an advantage when accessing nectar from deep-tubed flowers but we might imagine them to be unnecessarily cumbersome in feeding from a flower head of ragwort for instance crowded with other insects. Butterflies that feed on honeydew, and fruit juice feeders often have modified proboscises with a sponge-like structure at the ends which enable them to soak up this kind of food.
A Taste for Rotting Fruit Some kinds of butterfly indulge in yet another alternative to nectar, namely rotting fruit. The adjacent photo reveals a Red Admiral indulging in its well-known activity of sucking the juices from a rotting apple. They obligingly wait until the fruit is on the ground and of no use to us before tucking in. and Sweat As well as snacking on these sugary drinks, many kinds of butterfly, but often just the males, take fluid from loose soil or sweat from your hand, presumably attracted by the salt content as well as the water itself.
Food for Thought If we start to consider the nectar needs and preferences of individual species it can be a lot more complicated than that but unless we are focused on conserving one particular species, we don't want to waste time overthinking things. Go ahead, purchase and sow a good nectar mix to start attracting butterflies to your garden, Then go through a list, like ours, of caterpillar food plants, identify those suitable for the caterpillars of the butterflies likely to be around in your part of the country. Check that they are in the commercial wildflower mix, and if they are not - usually because they don't produce pretty wild flowers for pollinators - purchase them separately, either as seed or plug plants. The advantage of plug plants is that they provide a head start over everything else. To persuade butterflies to actually breed in your garden rather than just stop for a nectar snack the caterpillar food plants must always take precedence.
Nectar and Moths You may have noticed that many plants, like the high yielding nectar plants like dandelions, as well as many popular none-native species like the African daisies (Osteospermum spp.) and the bindweed look-alike Convolvulus cneorum close their flowers at night. This means that their nectar is not available to the lepidopteron nightshift, namely the countless species of moths that must need it to fuel their flight - or do they? As they make up a significant part of the diet of bats, and supply the all-important abundance of caterpillars for nestling birds, moths are even more important to the food chain than butterflies. It is clearly important therefore to sow a wide range of nectar plants and maintain and encourage pre-existing ones, at least some of which will keep their flowers open at night, or even, like honeysuckle open them specially to welcome moths.
A Starvation Diet A lot of moths have bypassed the problem of a shortage of winter and night-time nectar plants by not feeding as an adult anyway; but so few moths have been studied in detail that it’s hard to hazard a guess at a percentage. Several common moths don't take food at all as adults. These include the Wood Tiger Moth, Oak Eggar and Goat Moth. They rely throughout their adult lives upon the food laid down as caterpillars, to enable them to produce a large number of viable, full-sized eggs, and have the stamina to fly around in search of a mate and suitable food plants on which to lay their eggs. This emphasises the importance of a high quality diet for the caterpillars if the adults are to produce a healthy new generation. This applies not only to those species of moth that do not feed as adults. Butterflies do feed as adults but sugary nectar itself is far from constituting a balanced diet, so it might be assumed that well-fed caterpillars are essential to produce a generation of strong healthy adults in all butterflies, Even if its effects are not seen immediately, a sub-optimal diet over a few generations can result in a serious weakening of the viability of a colony of butterflies or moths. The importance of larval food plants cannot be emphasised too strongly. Pollinators, like butterflies and moths, start out as caterpillars and in order to develop into healthy adults depend on the leaves of specific wildflowers for their nutrition, the very wildflowers that fall victim to over-intensive agriculture, local authority strimmers and herbicide sprays, and the dismal paving over of gardens. But we are now at the situation where in many areas of the country even non-specific nectar-producing flowers, exotic as well as native, are in desperately short supply.
Setting up Home Once we have equipped our area with nectar stations at which passing butterflies can refuel, we don’t really want them to continue their journey. We would prefer them to stay, set up home and produce the next generation. So if we wish to create a breeding ground for butterflies, the next step is to see how well the commercial pollinator mixes supply the necessary caterpillar food plants. It’s easy enough. Just go through a list like ours of caterpillar food plants, and identify those suitable for the caterpillars of the butterflies likely to be around in your part of the country. Then check that they are in the commercial wildflower mixes of interest to you, and if they are not - usually because they don't produce pretty wild flowers for pollinators – simply purchase them separately, either as seed or plug plants. The advantage of plug plants is that they provide a head start over everything else growing from seeds. To persuade butterflies to actually breed in your garden rather than just stopping briefly to refuel at its nectar pumps, it’s important that the caterpillar foodplants always take precedence.