Many people are antagonistic towards ivy, believing that it will kill a tree a tree it climbs up. Ivy is not a parasite, it is an epiphyte that merely uses support – a tree, fence of wall, -to reach the light. This misbelief that ivy is damaging to a tree is probably founded on the way ivy thrives on dead trees without any leaves. It does, however, increase the wind resistance of a tree and make it more susceptible to being blown down by storm winds. Local councils wage war on ivy, because if an ivy-covered tree is blown down damaging a house or blocking a road, the Council can be held responsible and sued. The solution adopted is to cut a metre out of the base of the growing ivy so that it dies back without, however, is making any attempt to clear away the dead foliage. This results in the tree becomes unsightly until the dead ivy branches rot away.
When it first begins to grow ivy has five-lobed palmate leaves, but once it has reached the light it changes to producing simple leaves and begins to flower. Its flowering season is from September into November when there are few other sources of nectar. The flowers are light green in colour and are produced in globular clusters. They emit a pungent scent, which some people find unpleasant. It is this scent that, both by day and by night, attracts a wide miscellany of animals to feed on the copious quantities of nectar the flowers produce. In late autumn there are few other sources of energy the nectar provides for insects and other animals either preparing to overwinter or migrate south to warner climes. As a result, every patch of flowering ivy becomes a Mecca for all manner of foraging insects and other invertebrates, many of which are important pollinators. On sunny days the loud buzz of insect visitors is audible, but at night it is quieter and there is an almost complete change in the types of visitor. My attitude to ivy underwent a major shift once I began to photograph visitors to the ivy blossom and realised just how many there are and their great variety. There are two shifts one by day and an almost complete change of species at night.
The day shift
When there are bee-hives within a mile of an ivy patch, it will be worked extensively by honey bees. The discerning eye may notice that some of these bees look somewhat different, being slightly smaller and more crisply coloured. These will be ivy bees Colletes hederae; they are harmless solitary bees that only occur in autumn and specialise in the exploitation of ivy blossom. They nest individually in colonies of burrows excavated in bare sandy soil and lawns favouring sunny slopes. Find one of these bees, and the chances are there will be lots more around. In common with many other solitary bees, the males emerge first in early autumn and then hang around waiting for the females to appear. The first females to emerge are often targeted by hoards of males that form a ball all competing for the single female in the middle. Scientifically these bees are quite novel discovered in Europe in 1993. They were first found in Britain in 2001 arriving in Surrey in 2007 and in Farnham in 2013. It has spread rapidly and is now common throughout much of England and Wales.
Bees belong to the order of insects called Hymenoptera. Many other hymenopterare common visitors to ivy. You can see queen white-tailed bumblebees stocking on their food reserves so they can overwinter successfully and establish new colonies in the Spring. Several species of wasp exploit ivy flowers. On our local ivy patch at the edge of Ten-acre Wood was worked by large numbers of common wasp and sever of the larger saxon and tree wasps. These different wasp species are difficult to distinguish but have different nesting habits. Many people are scarce of them because of their painful stings, but they do provide a much-needed service in killing many insect pests – without wasps we would be plagued by flies and mosquitoes! However, the largest of the hymenopterans is the hornet, which has a fearsome reputation mainly created by its portrayal in children’s comics. Queen hornets forage on ivy flowers both by day and by night, and pollen can be seen adhering to the hairs on their legs and bodies. Hornets are much less aggressive than the smaller wasps and are quite approachable unless of course you are meddling with their nests.
A rich assortment of flies visit ivy flowers including several species of ‘bluebottle’, ‘green-bottle’, ‘house flies’ and hoverflies. Hoverflies are almost as important pollinators as honeybees. Several of the species have a black and yellow coloration which mimics the colorations of wasps and hornets and it is easy to be taken in by this disguise. But look at a fly closely and you will see that it has just one pair of wings (bees and wasps have two pairs). The hind wings are modified into dumbbell shaped sensory structures called halteres that are sensory organs that help a fly to stabilize its flight. Halteres are most easily seen on daddy-longlegs as white knobbed bars just behind the insertion of the large wings. Perhaps the oddest of the flies you may see on Ivy are conopid flies. They are rather bizarrely shaped flies and again have a coloration mimicking that of wasps. Their larvae are internal parasites of bees and wasps; In France, the larvae of one species has been reported as a parasite of queen Asian hornets.
The most colourful insects regularly seen on ivy flowers are butterflies. The red admiral butterfly (Vanessa Atalanta) is the most striking. It can be seen flying throughout the year on warm sunny days, I have even seen it feeding on the flowers of sweet box Sarcococca on a sunny day in January. Not all red admirals are resident. Each year there is a big influx of red admirals migrates across the Channel from Europe in mid-May and these immigrants lay their eggs singly on nettles. In autumn they all used to migrate back to Southern Europe, but now, increasingly more, overwinter here. You may find them in sheltered frost-free hide-ways like your garden shed. Thus year (2017) they have been very common feeding on the flowers of our local ivy patch om sunny days. While early in the autumn most will have been fuelling up for their migration back across the Channel, the later ones will have been preparing for hibernation and looking for frost -free shelters. Another butterfly that exploits ivy is the Comma (Polygonia c-album). At the beginning of the 20th century this was a rare butterfly, but in the 1930’s, it changed from using from using hop to nettle as its larval foodplant and became common. With its wings open it is striking, but when it closes its wings it looks like a dead leaf. It occurs throughout Surrey and there are two generations, the first in Spring (mid-March until May) and the second is on the wing from late June until October. It is this second generation that can be seen visiting ivy flowers in preparation for hibernation. Another butterfly that frequents ivy is the holly blue (Celastrina argiolus) but it does not visit for the nectar. It has two generations. In Spring the first generation lays its eggs on holly; the second generation which appears in late summer and it lays its eggs on ivy. The caterpillars can be found feeding on the buds of ivy in September. Holly blue populations fluctuate extensively because of a parasitic ichneumon wasp. The wasp lays a single egg within the egg of the butterfly. The larva that hatches then lives inside the butterfly caterpillar without killing it. However, when the caterpillar pupates the wasp breaks out, killing its host. As a result, there are marked interannual oscillations in the abundance of holly blues, with a two-year lag between the peaks of abundances of the butterfly and its parasite. When the wasp is abundant it almost wipes out the butterfly locally, so the following year the wasp population crashes and the butterfly can begin to recover.
The night shift
Searching the flowers at night by torchlight reveals a whole different assemblage of animals exploiting the nectar some of which I find surprising. For example, many woodlice make the long climb from the ground to reach the flowers where they are joined by snails, ants and earwigs. Earwigs have wings but are reluctant fliers, so they too must climb up from ground level. Wasps and hornets are slight active at night, but less so than by day. Females of the common rough woodlouse Porcellio scaber are common visitors – this is the woodlouse species that you are most likely to find wandering around in your house. An efficacious treatment for stomach ache was once considered to be to eat woodlice! Woodlice are vegetarian, normally consuming decaying plant material but at night can be seen on tree trunks where they are eating the algae. Another frequent night-time visitor is the white-legged snake Millipede Tachypodoiulus niger. Millipedes are vegetarians and can and have two pairs of legs per segment, whereas the carnivorous centipedes have a single pair. Like the woodlouse they can frequently be seen at night climbing up the trunks of trees; presumably they are drawn to the flowers by their scent. On the ivy flowerheads they are often joined by banded snails
A common insect visitor that is capable of flight but rarely seem to do so, is the earwig Forficula auricularia. Again it seems to be the female earwigs that seem to visit the ivy. The sexes of earwigs can be distinguished by the shape and size of the back pincers; these are broader and strongly curved in males, but straighter and slimmer in females; (there is also a difference in the number of abdominal segments 8 in females and ten in males). The females lay their eggs in autumn and then tend the young after they hatch; presumably they are exploiting the nectar to stock up their energy reserves before reproduction.
Daddy-long-legs (or crane flies) are large members of the fly family that are mainly active at night, but are easily disturbed from grassland during the day. They are unpopular with gardeners because their larvae, known as leatherjackets, eat the roots of grasses causing unsightly bare patches in lawns. Again it is the females that are the common visitors to ivy flowers, squashing their heads against the flowers to get at the nectar.
It is the moths that are attracted to the ivy that interest me most. At night using a head-torch they can be picked out by their eye shine; the brightest eye shine being reflected from the eyes of the angle shades moth (Phlogophora meticulosa). This year (2017) one of the main themes for National Moth Night which was held in October was moths visiting ivy. This year, I recorded 21 species visiting our local ivy patch near Ten Acre Wood. The most abundant species was the chestnut (Conistra vaccinii), which is a moth that can occur throughout the winter months on relatively warm nights. In the autumn it favours ivy flowers but in Spring it is a common visitor to sallow catkins. This year, brick moths (Agrochola circellaris) were the second most abundant moth visitor, closely followed in abundance by red-line quakers (Agrocholqa lota) and yellow-line quakers (Agrochola macilenta). The less common species included a frosted orange (Gortyna flavago), several large ranunculus (Polymixis flavicincta) and a couple of pink-barred sallows (Xanthia togata) – some of the prettier autumnal moths. Other visitors, like a snout (Hyperia proboscidalis) and a common plume (Emmelina mondactyla), which I saw just once, are far more abundant earlier in the year. The plume moth looks like a mosquito when it is flying. More special visitors were several dark sword-grass moths (Agrotis ipsilon) and the rare large and spectacular clifden nonpareil (Catocala fraxini), both of which were probably migrants from Europe.
Thus, ivy is a hugely beneficial in the way it helps to sustain our biodiversity by supplying energy resources at a critical time of year to many insects and other species preparing for winter. Furthermore, during the winter the crop of ivy berries that are produced as a result of these visitors to the flowers are important as a food resources for many of our overwintering birds.