|The effects of the Harlequin Ladybird in Nottinghamshire|
|Along with many other naturalists, newspaper columnists and website owners, we wrote a great deal on the invasive Harlequin Ladybird and it's arrival in Nottinghamshire almost a decade ago.|
|The Harlequin Ladybird (Harmonia axyridis) first appeared in the UK in 2004. Soon
after it's arrival, it was exceptionally quick to
colonise new areas of the country, whilst substantially
strengthening its existing populations in the south-east.
Within the space of a couple of years, it had reached the north-west of England and the Welsh borders.
first acceptable record was from Eakring in July 2006,
although there is little doubt that it had already become
well established in parts of Nottinghamshire as early as
late 2005. One was claimed from Wollaton at the time, but
the record could not be accepted by the county recorder,
on the basis of lack of photographic evidence or
The Eakring record initially seemed to be an isolated one, but a few weeks later, we eventually discovered numbers of Harlequin Ladybirds at Hare Hill Wood near Kersall and in early November we counted 151 adults. By January 2007, most of the Harlequins at Hare Hill Wood had disappeared, but we did find a small over-wintering group under loose bark and in company with a number of 2-spot Ladybirds. Along with literally hundreds of other invertebrates, the 2-spot Ladybird was just one of many species of Ladybird deemed threatened following the Harlequin's UK arrival.
Native Ladybirds at risk
We have made regular counts since 2006, so we thought that it might be time to look at our Ladybird records further, to see if there has been any sign of the predicted dramatic decline in the numbers of our native Ladybirds.
The species we thought to be most at risk ,would be the 2, 7, 10 and 14-spot, Orange, Cream-spot and Pine Ladybirds. We've classed these Ladybirds most at risk, because they often share a preference for Lime, Beech and Sycamore trees, which the Harlequin often favours. In urban areas, Lime and Sycamore trees used in urban street-planting schemes for years, are particularly attractive to Ladybirds, as they are more prone to developing large accumulations of Aphids, more than most other trees.
As our records date back to when the Harlequin first arrived in Nottinghamshire, we have looked at the total number of individuals of each species recorded since then and have included our latest records for 2014. The graph below shows our annual Ladybird counts dating from 2006 to 2014. We have not included the data for both Harlequin and 7-spot Ladybirds in this graph, as the pure size of their counts in some years, renders the smaller counts of the other six species almost invisible.
|The 7-spot Ladybird is
still usually found in much larger numbers, especially in
more rural locations. Most times, it is just far less
obvious than it's gregarious Asian counterpart. It is
however, prone to attack by a parasitic wasp (Perilitus
coccinellae) and in 2011, we found that approximately
20% of adult 7-spot Ladybirds were affected over all of
the sites we visited that year. A similar natural
population control, has yet to be recorded attacking the
Although both species congregate in numbers during the last warm days of the Autumn, the Harlequin is greatly attracted to light, warm objects. The trunks of large Beech trees and the walls of churches are especially attractive to the Harlequin as they search for somewhere to over-winter, while the 7-spot will be found in much the same numbers, but mostly on low foliage and leaf litter.
Large numbers of Harlequins in urban locations, often give rise to the belief that they out-number the 7-spot, yet we have found that they rarely actually do. The warmer climate generated by the concrete and brick buildings of our towns and cities, may well help Harlequin Ladybirds to successfully overwinter and they are more likely to hibernate indoors than other Ladybirds. 7-spot Ladybirds prefer to overwinter in leaf litter, or openly on evergreen shrubs and small trees, even in urban locations.
Potentially, its the other species not mentioned in any detail so far, which are most at risk, but we have personally yet to record any long term drop in the numbers of 2, 10 and 14-spot, Orange, Cream-spot and Pine Ladybirds. What we have seen though, are strong fluctuations within the populations of all species, including the 7-spot and Harlequin Ladybirds.
On producing the data in Tables 01 and 02, it was obvious that there have been two 'Ladybird' years in 2011 and 2012. While 2006 was good for four of the selected species, the Harlequin was only just establishing itself and the 7-spot Ladybird had a poor year by more recent standards.
If we are to take the 2006 data as providing a suitable baseline and assume it to be an average year for Ladybirds, then there followed four poor years (2007-2010) good years in 2011 and 2012, then poor years in 2013 and 2014. Several years ago, we mentioned that many species of Ladybird have a cycle of three to four poor years, before building up in numbers to a good year. At the moment, this still seems to be the case and we cannot find anything in our data which would suggest otherwise.
|It must be remembered
that we are only concerned with Nottinghamshire here, so
the picture from other parts of the UK may well be
different, although we believe unlikely. The after
effects of the Harlequin's arrival, may also be more
evident in urban areas, something which could make a very
useful study in schools?
Table 01 shows the fortunes of the eight species selected. The figures in the GLr column, are the annual counts, of which anything above would represent a good year. For example - a total annual count of above 60, would class the 2-spot Ladybird as having had a good year.
|Our records show that the likely affected species, either have mostly low population levels anyway, or are predominantly arboreal and less likely to be seen, but will occur in higher numbers when favourable conditions arise. Weather/climatic conditions at certain times of the year, will be one determining factor to the fortunes of all species. We consider changes to habitat or habitat loss, to be a less likely factor for our selected species, as all frequently occur in urban areas and are not habitat specific.|
|Table 02 shows our
Ladybird counts for each year since 2006.
The two rows in blue, show the combined totals of all species (Totals 1) with the same totals, minus those of the 7-spot and Harlequin in Totals 2.
We have never recorded either Orange or Cream-spot Ladybirds in any real numbers and our records consist of single individuals (or very rarely) small groups. Both have proved to have low population levels based on our records.
The Pine Ladybird is another species, more usually found in small numbers, but it does occasionally have years of abundance.
Summary of the records and conclusion
Having looked at the results we have gathered over almost a decade, we can find no data to suggest that the arrival of the Harlequin Ladybird has so far had any detrimental effect on our native Ladybirds.
Our counts have come from various habitat types, in which the Harlequin was found in all at some time. So far, all species appear to have been unaffected by the Harlequin's arrival here and while this may be down to a similar size in both the adult and larval stage of large species such as the 7-spot Ladybird, this would not apply to the other six species which are smaller.
and 14-spot Ladybirds are more species of the lower shrub
layer, being less arboreal in their habits than the
Harlequin, so there should be less competition for food
between these Ladybirds, either when adult or larva.
Competition for food by the Harlequin is (potentially)
more likely to affect the 2-spot, 10-spot, Cream-spot and
Pine Ladybirds, which are often arboreal.
We still regularly find trees in Market Warsop, on which the 2-spot Ladybird lives quite happily with large numbers of Harlequins and the two species will often overwinter together. Similarly, a large Honesuckle in our own garden usually holds several 7-spot, 10-spot and Harlequin Ladybirds in the Spring and late Summer. While the Orange Ladybird is another arboreal species, there is no competition for food in either the adult or larval stage, as it is mycetophagous (fungus eating) and lives on mildews found on leaves.
However, any large Ladybird larva finding one smaller than itself, or finding a larva in the early stages of pupation, will be opportunistic and take an easy meal. Both 7-spot and Harlequin larvae will do this and we have found cannibalism occurs more frequently in the Autumn, when Aphids leave the trees and the Ladybird's natural prey declines.
So what is likely to happen to our native Ladybirds in the future?
We still believe that the annual populations of the 2, 10 and 14-spot, Orange, Cream-spot and Pine Ladybirds, will remain relatively stable across all habitat types, with occasional years of abundance as has been shown. These all tend to occur at low density population levels. There is also nothing to suggest to us, that the 7-spot Ladybird will suffer any more than the Harlequin Ladybird and that whatever the governing factors leading to years of abundance for both species are, appear to be shared.
The Harlequin Ladybird is now well established as part of our invertebrate fauna. It will never be able to be controlled or eradicated by man, so we should just accept that it is here to stay. There will certainly be more invasive species that will reach our shores over the coming years and some of these, may really be harmful to some of our native insects and plants. These are the species we should really be monitoring and looking out for.