#GBB13 - The Green Shieldbug

This post is the latest in a series covering the ID of a selection of species which are likely to be in and around everyone's gardens, parks, etc, created for the 2013 Garden Bioblitz (details at http://www.naturewatched.org/gbb.html - everyone join in!)

The Green Shieldbug, Palomena prasina has got one of those really functional names. It's a green, shield-shaped bug, around 13mm long:
It does have a few bits that aren't green though: reddish antennae and tarsi (feet) stand out from the background, and puncture marks and the exposed wing membranes at the back are darker.  This splits the Green Shieldbug from the only similar species in the UK, the introduced Southern Green Shieldbug (Nezara viridis) - that species is a uniform green as an adult, with light green wing membranes, few to none dark puncture marks, and 3-5 indistinct white marks on the front of the scutellum. Native to Africa but a regular find in Britain since 2003, it has a much smaller distribution (mainly in the south-east) than the widespread and common native species.

In autumn, the adult shieldbug changes from green to a bronzey, purpley colouration to be camouflaged through the winter, which is spent lurking in leaf litter and low vegetation. They're still purpleish when they begin reappearing in April-May, but quickly regain their green colouration in time for summer.  Come June, the first eggs appear: batches of 20-30 barrel-shaped, bright green eggs laid with geometric precision in a hexagonal pattern on leaves.  As sap-feeders on a range of deciduous trees and shrubs, especially hazel, the nymphs can begin feeding straight away.

Unlike the familiar 4-stage life cycle of butterflies, with a pupal stage where the larva changes to an adult, shieldbugs only have 3 stages: egg, nymph, and adult. The nymph sheds its skin several times, gradually looking more and more like the adult, before shedding its skin one last time to reveal the adult, recognisable from the full wings - nymphs aren't capable of flight.
Nymphs of the Green Shieldbug are green, red or orange when they first hatch, but soon darken to green, often with a darker head, thorax and wing buds, like a smaller, rounder version of the adult. They're easily distinguished from the Southern Green Shieldbug  at this stage, as the introduced species has black nymphs, speckled with patches of bright yellow and red. Although it does have a green form, this too is speckled with yellow, red and black

More information on the Green Shieldbug, including illustrations of the nymphal stages, can be found at the excellent British Bugs website: http://www.britishbugs.org.uk/heteroptera/Pentatomidae/palomena_prasina.html and there's also a Field Studies Council fold-out chart available to buy at http://www.field-studies-council.org/publications/pubs/shieldbugs-of-the-british-isles.aspx

Any sightings should be sent to the Heteroptera recording scheme, or recorded online at http://www.brc.ac.uk/iRecord/

And of course, don't forget to join in with the Garden Bioblitz on the 1st/2nd June 2013! http://www.naturewatched.org/gbb.html for more details

#GBB13 - The 7-spot ladybird

This post is the first in a series covering the ID of a selection of species which are likely to be in and around everyone's gardens, parks, etc, created for the 2013 Garden Bioblitz (details at http://www.naturewatched.org/gbb.html - everyone join in!)

The 7-spot ladybird, Coccinella septempunctata, is the archetypal ladybird. Featured in toys, games and company logos, this is one of the very few insect species with a positive public image - in fact, it's nicknamed 'the gardener's friend' for its habit of devouring pest insects such as aphids.


An adult 7-spot ladybird, sunbathing to warm up

The adults are amongst the easiest insects to identify - big (5-8mm long) and bright orange, they make no effort to hide (their bright colours are a warning to predators of their foul taste), and they only come in one colour form, unlike species such as the 2-spot or Harlequin ladybirds (the snowflakes of the insect world, with no two individuals alike).

99.9% of the 7-spots you'll ever see will look almost exactly like the one pictured above - the wing cases (elytra) a bright orange/red, with a pyramid of three roundish black spots on each, and a 7th stretched across both elytra at the front, just behind the black-and-white head and thorax. Occasionally specimens miss spots, or have tiny extra ones, but in general, the picture is what they'll look like.

As a double-check, the 7-spot is one of the largest ladybirds in Britain - most of our 47 species are less than 5mm long. The only species which can look similar, and is a similar size, is the Harlequin (Harmonia axyridis), which can sometimes have very few spots, but the orange colour form of the Harlequin always has a black 'M' on the thorax, which is never present in the 7-spot.

Definitely not a 7-spot ladybird. The spotless form of the Harlequin ladybird - note the 'M' marking

Ladybirds, like most insects, have the 4-stage life cycle familiar from butterflies - egg, larva, pupa, adult. In butterflies and moths the stages can have different names - caterpillar for the larva and chrysalis for the pupa, for example - but with ladybirds, it's just egg, larva, pupa, adult.  Although not as easy as the adult, it's still entirely possible to successfully identify pupae and fully-grown larvae of the 7-spot.

Pupa of a 7-spot ladybird

A lot of people will have seen a ladybird pupa without realising what the strange, blob-like creature on the leaf actually was, and it's true, they do look a bit odd - especially when they feel threatened and rear up and down like a globular hinge! Only found in the vicinity of aphids, 7-spot pupae are rounded, orange-and-black, and big enough to fit an adult ladybird inside them (again, much larger than most of the other ladybird species), and with the shed skin of the larva at the back end, where it's attached to the leaf. The shed skin is an important feature for distinguishing 7-spot pupae from Harlequins, which are brighter orange and have a very spiky shed larval skin.

Not a 7-spot. A Harlequin ladybird pupa, note the brighter orange and obvious spines on the shed larval skin

The combination of size and lack of spines is a good pointer for the larvae, too. Again, they're big, and covered in warts (not spines), and they have a couple of orange flashes on either side, each made up of two warts, one on top of the other. There are a few fairly similar species, but none of them have the combination of large size and the 4 orange patches.  They have a voracious appetite for aphids, and you won't find them far from an aphid colony (or underneath one).


Two views of 7-spot ladybird larvae

Any ladybirds you see should be recorded at the UK Ladybird Survey website (http://www.ladybird-survey.org/), which is also well worth looking at for the other species, and for lots more information besides.  There are also plenty of ladybird photos on the web - my Flickr sets are below:

Adult ladybirds - http://www.flickr.com/photos/rcomont/sets/72157623774877905/

Pupae - http://www.flickr.com/photos/rcomont/sets/72157626283897399/

Larvae - http://www.flickr.com/photos/rcomont/sets/72157626283897399/

If you prefer paper, the Field Studies Council also publish ID charts for the ID of adult (http://www.field-studies-council.org/publications/pubs/guide-to-ladybirds-of-the-british-isles.aspx) and larval ladybirds (http://www.field-studies-council.org/publications/pubs/ladybird-larvae.aspx)

And of course, don't forget to join in with the Garden Bioblitz on the 1st/2nd June 2013! http://www.naturewatched.org/gbb.html for more details

Aliens vs Invasives

Over the last couple of days,a couple of people on Twitter have flagged up a Comment Is Free article on alien species (http://www.guardian.co.uk/commentisfree/2013/feb/23/alien-species-british-countryside-kneejerk-nature?CMP=twt_gu).  It's not a bad article (although as ever, don't bother reading the comments), but it manages to confuse & combine alien with invasive and effectively ends up arguing strongly for the status quo.

Alien species are not necessarily invasive. The two terms are often heard - often used - together, but in fact, the two are very different.  The official definition of an alien species (from the IUCN via the Convention on Biological Diversity, CBD: http://www.cbd.int/invasive/terms.shtml) is 'a species, subspecies, or lower taxon occurring outside of its natural range (past or present) and dispersal potential (i.e. outside the range it occupies naturally or could not occupy without direct or indirect introduction or care by humans) and includes any part, gametes or propagule of such species that might survive and subsequently reproduce' - basically, it's a species which people have moved to a new area.  

A recent review of the non-nativeness of the British countryside (overall, about 0.5%: data at http://www.brc.ac.uk/downloads/English%20Nature%20Non-native%20Audit%20report%20662.xls)  found that more than 2,700 alien species are at large in Britain, from Neolithic introductions such as the Large Tabby moth (Aglossa pinguinalis) to very recent arrivals like the Demon shrimp (Dikerogammarus haemobaphes).  A study on plants in Britain (Williamson & Fitter, 1996) found that, of every 100 alien species introduced to a new area, only 10 will establish wild populations, and only 1 will go on to become invasive.  In this context, 'invasive' has a strict definition, again from the CBD: a species which 'is an agent of change, and threatens native biological diversity'.  

This is the crux of the matter. An alien species may be invasive - for instance Himalayan Balsam (Impatiens glandulifera), Japanese Knotweed (Fallopia japonica), and the Harlequin ladybird (Harmonia axyridis), but so can native species. A decade ago now, I worked for the RSPB at their Aylesbeare Common reserve, a heathland site in East Devon. We spent a huge proportion of our time chopping down and otherwise killing plants which were invasive on the heathland - all of them natives, mainly Silver Birch (Betula pendula), Bracken (Pteridium aquilinum), and Bramble (Rubus fruticosus agg).  Aliens, like the pine trees scattered across the heathland, we generally left alone - they weren't spreading, so weren't invasive, so weren't a problem.

Some alien species can go beyond this, and become integral to an ecosystem. The rabbits (Oryctolagus cuniculus), mentioned in the CIF article as a long-established alien species, are crucial to the maintenance of chalk downland, and the 1950s/60s outbreak of myxomatosis in rabbit populations contributed significantly to the extinction of the Large Blue butterfly (Maculinea arion) and the near-extinction of at least three more butterfly species.

Of course, some aliens are disruptive, and there's no good way of predicting which species will establish, and which will displace or feed on natives, becoming problematic invasives. That's why border controls are strict: they're based on the precautionary principle.  We can't tell which species will cause havoc when they arrive, and it's virtually impossible to eradicate a species once it's established, so the best bet is to prevent arrival in the first place.

Some of the most notorious alien species are invasives.  The Harlequin ladybird has been linked to significant declines in native ladybirds (Roy et al., 2012), and the effects of Rhododendron & Japanese Knotweed are well known, but the vast majority of alien species fall between these two extremes.  These species lead lives of quiet obscurity with few, if any, effects on native ecosystems, like the Bryony ladybird (Henosepilachna argus) in Surrey or the Yellow-tailed Scorpions (Euscorpius flavicaudis) in Sheerness.  Consequently there's no control measures for them - they may be aliens, but they come in peace.

The flexible approach - taking each case on its merits - is presented as the big message at the end of the CIF article. But it's already common practice with alien species, in Britain and far beyond. The mere fact of a species' origin is, in practical terms, essentially immaterial: what's important is the effect it has on native ecosystems, adapted to the local area and each other.  


Refs:

Roy, H.E., Adriaens, T., Isaac, N.J.B., Kenis, M., Onkelinx, T., San Martin, G., Brown, P.M.J., Hautier, L., Poland, R.L., Roy, D.B., Comont, R., Eschen, R., Frost, R., Zindel, R., Van Vlaenderen, J., Nedvěd, O., Ravn, H.P., Grégoire, J.-C., de Biseau, J.-C. & Maes, D. (2012b) Invasive alien predator causes rapid declines of native European ladybirds. Diversity and Distributions, 18, 717-725.

Williamson, M. & Fitter, A. (1996) The Varying Success of Invaders. Ecology, 77, 1661-1666.

Web ID resources

This page has now moved to http://www.richardcomont.com/p/id-resources.html

Big groups of ladybirds in the autumn - why?

Ladybirds.  They're creatures of summer, right?  So why are there big groups of them around in the autumn, hundreds on walls, cars, or even coming into houses?


A comparatively small aggregation of Harlequin ladybirds, here aggregating in a straw hat.

It's because Britain is in the grip of an alien invasion: the non-native Harlequin ladybird, Harmonia axyridis.  This large species (5-9mm long) is native to Asia (Japan, China, Russia & the Koreas), and was first found in Britain in 2003, flying the Channel after being introduced into continental Europe as a biocontrol agent, to eat aphids in hop gardens and roses.  A very variable species, it comes in three forms in the UK: forms conspicua and spectabilis, which are black with two and four red spots respectively, and form succinea, which is orange with 19 black spots (although some or even all of them may be absent, or they can fuse together).  Around 80% of the British Harlequins are form succinea, but even so, like snowflakes, no two are exactly alike.

But why are they still about in late autumn?  And why do they form these big groups?
Well, the Harlequin is a species which can breed all year round, and has two or even three generations a year (whereas most of our 25 native species will only have one), so they take that extra time before entering overwintering.  And as for the big groups?  Well, each female Harlequin can lay up to 2,200 eggs under ideal conditions, so by the end of the summer there are huge numbers of them about, all looking for somewhere cozy to spend the winter.

In the native range, the Harlequin spends the winter in these groups - aggregations - in the mountains, forming groups in the mouths of caves and underneath rocks.  In the introduced range - some 50 or more countries in Europe, north & south America, & Africa - houses, sheds, porches and the like take the place of these natural refuges.  During the early autumn, the ladybirds form large swarms and begin to seek out overwintering locations.  They find them by using a mixture of visual and chemical cues, often aggregating in buildings that are distinct from their surroundings, and pale - white attracts more than yellow, which in turn attracts more than darker colours. 

Once they're in the vicinity, the swarms will seek out chemical cues laid down by their grandparent's generation, stable long-chain hydrocarbons which they can detect with their antennae - that's why aggregations form year after year on the same spot.

One last thing: Harlequins aren't the only species to form aggregations.  Two-spot ladybirds will group together in houses, and many species will do it outside - Orange, Pine, & 7-spot ladybirds, to name just a few!  The UK Ladybird Survey are always glad of any winter records - the website is http://www.ladybird-survey.org/