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Species of the month

Every month it is our aim to highlight a species that is “in-season” and, although not necessarily rare or difficult to identify, has been highlighted by our local recording groups as being somewhat under-recorded and for which new records would therefore be welcomed.

If you or your recording group are aware of species such as this then please contact Bob Foreman.

 

April: Holly Blue Celastrina argiolus

Holly Blue - Nigel Kemp

A spring brood female Holly Blue
Photo: Nigel Kemp

Holly Blue - Nigel Symington

Holly blue underside, freckled with delicate black spots
Photo: Nigel Symington

Holly Blue distribution map

Distribution of Holly Blue records in Sussex between 2010 - 2014
Reproduced from The Butterflies of Sussex by Michael Blencowe and Neil Hulme

There are seven ‘blue’ butterfly species resident in Sussex but during a global viral pandemic the chances of seeing them all are limited. Many of them are tied to specific food plants, specialised habitats and flight times and therefore may be out of reach if you are quarantined in a two-bedroom terraced house in Haywards Heath for six months.

However, there are two ‘blues’ that are within reach of all of us during these challenging times. The Common Blue Polyommatus icarus lives up to its name. It primarily feeds on Common Bird’s-foot-trefoil Lotus corniculatus and subsequently can be found in gardens, meadows and verges where this plant grows. But for many of us struggling through this Covid-19 pandemic an even commoner sighting will be the Holly Blue Celastrina argiolus.

The Holly Blue is a true garden butterfly and the urban areas of Sussex (where most of us find ourselves trapped at the moment) are the perfect habitat for this species. Its here it finds abundant shelter and pockets of warmth amongst our territorial terrain of fences and walls. Importantly its larval foodplants, Holly Ilex aquifolium and Ivy Hedera Helix) are abundant in our residential landscape.

The Holly Blue will have spent the wet winter of 2019/2020 in the pupal stage and will be emerging around about now as part of the year’s first brood (April-June). They will feed, meet and mate and the female will search our towns for suitable egg-laying sites. In the spring they lay eggs mostly on Holly. The caterpillars munch on the flowerbuds, pupate and produce a second brood (July-September) which emerges in the summer. Females from this brood will mainly lay on a different foodplant: Ivy. In some years a small third brood flies in October.

While other blues which are strictly confined to their communities like humans during a pandemic the Holly Blue breaks all the restrictions and roams around our towns like some carefree super-spreader. You’ll most likely see it jittering around in the treetops where you’ll look up and glimpse its silvery grey underwings (unless you’re confined to a 6th storey flat in Hove where you’ll be looking down on the vivid blue of the upperwings). If it settles on a leaf, and you are lucky to get up close, you’ll see these silvery underwings are freckled with delicate black spots.

The butterfly’s population is intimately tied to a parasite - Listrodomus nycthemerus which exclusively parasitises the Holly Blue. This ichneumon wasp uses a slender ovipositor to lay eggs into the Holly Blue’s caterpillar. The wasp’s larvae feed and develop inside the caterpillar and an adult wasp emerges from the butterfly’s chrysalis. The result is a ‘boom and bust’ population cycle for the Holly Blue. The increase in the butterfly’s population is shadowed by that of the wasp until, when the wasp numbers reach their peak, the Holly Blue’s parasitised population is overwhelmed and spectacularly crashes. The wasp then has nothing to parasitise in subsequent years so, after shooting itself in one of its six feet, its population crashes too. This gives any remaining Holly Blues the chance to restock themselves... and the cycle starts again. This is why in some years you’ll see lots of Holly Blues where as in other years they seem rather scarce. Hopefully this current Human / Covid-19 situation isn’t the start of a similar boom/bust cycle. One thing’s for certain, there will be a lot of Holly Blues flying around Sussex in 2020 thinking to themselves “Where is everybody?”.

If you do see Holly Blues (or, for that matter, any other species of butterfly, aphid, moss, dragonfly, beetle, mammal, fungus, collembola, etc.) in your garden this spring, please record your sightings on the iRecord website.

Michael Blencowe
Emeritus professor of butterflyology, University of Small Dole

 

 

March: Urban gulls Larus sp.

Herring Gulls

Juvenile and adult Herring Gulls

Lesser Black-backed Gull

Lesser Black-backed Gull

Nest Site

Typical urban nest location

Out for the count with census to safeguard seabirds

Gulls are a familiar and traditional part of life in seaside towns. Often unfairly maligned by day-trippers and coastal residents alike as noisy scavengers, populations of these most misunderstood of seabirds are in decline.

There have been three censuses of breeding seabirds in Britain and Ireland since 1969. The last one, Seabird 2000, was completed in 2002. These censuses, and regular counts at the large rural colonies, have shown that Herring and Lesser Black-Backed Gull populations have plummeted, to the extent that Herring gulls are now red-listed as 60% of the population has been lost since 1969. Lesser Black-Backed Gulls are amber-listed as their population has also seen declines.

However, these trends are based only on coastal colony counts as the first two national censuses did not cover inland or urban areas. Seabird 2000 was the first attempt to get a picture of the urban gull population, and although there were some gaps, the major areas were covered. But we do not know whether the declines in rural populations are caused in part by a shift into towns.

Given the time since Seabird 2000, it is important that another census takes place, and therefore, Seabirds Count was developed by the Seabird Monitoring Programme (SMP), and is being co-ordinated by the Joint Nature Conservation Committee (JNCC). Its goal is to gather data on numbers of breeding seabirds, with the aim of understanding how distributions and populations have changed. Survey work started in 2015, and is finished for open coastal areas. The gap that remains is to complete the survey of the urban breeding gull population.

In 2019, volunteers returned to urban areas covered by Seabird 2000 to see whether the numbers had changed. Brighton and Hove is a key area in Sussex for breeding gulls but it appears there has been a decline in numbers. 360 Herring Gull territories were recorded in Seabird 2000, but only 270 in 2019. However, it is not known whether this is due to a shift in distribution to parts of the city that were not surveyed. Anecdotally, it seems that the move to covered bins and house renovations removing chimney pots have had an impact, though if this means the gull population is as a level where it is in less conflict with residents, then this is perhaps not a bad thing.

The last phase of the urban gull census is to survey a set of randomly generated 1km squares. This is the focus of the 2020 breeding season and will enable a population estimate to be derived for the urban gull population for the first time.

The survey is simple - just one visit is needed to the survey square in late-April to late-May. The aim is to cover all the built up part of the square from the ground, and count birds incubating or holding territory. As it is difficult to see all birds from the ground, the SMP partnership has developed a correction factor for different types of urban area, which will be applied to reach a population estimate.

Gull survey squares

1km squares in Sussex that need surveying
(For full list click on link below)

There are 100 squares in East and West Sussex that need surveying ( download list here). If you would like to help, please get in touch with Alison Giacomelli ( alison.giacomelli@naturalengland.org.uk) with where you live, and she will match you up with a survey square. Thank you!

 

 

February: Pseudoscorpions

Dendrochernes cyrneus

Phoretic Large Tree-chernes, Dendrochernes cyrneus (dry decaying ancient woodland), the largest British species, on an ichneumon.
Photo: © Steve F. Woodward

Roncus lubricus

Reddish Two-eyed Chelifer, Roncus lubricus (woodland leaf litter).
Photo: © Gerald Legg

Neobisium carcinoides

Moss neobisiid, Neobisium carcinoides (leaf litter, under stones).
Photo: © Gerald Legg

Lamprochernes nodosus

Knotty Shining-claw, Lamprochernes nodosus (compost and manure heaps).
Photo: © Gerald Legg

Spermatophore of Cheiridium

Spermatophore of the Book Pseudoscorpion, Cheiridium.
Photo: © Gerald Legg

Chthonius ischnocheles

Common Chthonid, Chthonius ischnocheles (leaf litter, under stones).
Photo: © N.A. Callow

Dactylochelifer latreilli

Marram Grass Chelifer, Dactylochelifer latreillii (sand dunes, salt marshes).
Photo: © Gerald Legg

Cheiridium museorum

Book Pseudoscorpion, Cheiridium museorum (barns, warehouses, thatch, old libraries, hen-houses, stables).
Photo: © Gerald Legg

Miniature Tigers - False-scorpions

Miniature hunters resembling tiny scorpions, but without the sting-tipped tail, can be found in your garden living amongst dead leaves, under tree bark, in compost heaps even in old store rooms and thatch. Like spiders and harvestmen, they have eight legs making them arachnids, the fourth largest group: the Pseudoscorpions or false-scorpions. Worldwide there are over 2000 species of which 28 occur in the British Isles and Ireland. They are never large animals, the biggest species, which is an undescribed one from Pakistan, is only 15mm long.

As top predators they play an important role in many habitats. Several are associated with man-made habitats and have been known for a long time, for instance the ‘Book-scorpion‘ of Aristotle, that preys on book-lice that eat parts of books. As aggressive hunters they catch their prey using their enlarged and lobster-like second pair of appendages, the pedipalps. These formidable weapons vary in shape and size depending on their favoured prey: stout strong ones for tough slow prey and thin delicate ones for fast moving thinner-skinned victims. Once caught the prey may be injected with fast-acting venom and then chewed by jaws called chelicerae as digestive juices are poured into their victim. The resulting soup is then sucked-up into the mouth.

Some species are eyeless others have either one or two pairs. These are only sensitive to light levels and cannot see detail. For a pseudoscorpion to accurately navigate, find prey and mate they feel their way using special long sensory hairs: the trichobothria, many of which occur on the pedipalps and are extremely sensitive to air movements. They also occur on the rear of the animal enabling it to know what is behind it. Other sense organs detect tiny traces of chemicals - they taste the air and surroundings.

The chelicerae of some species have a special knob or longer process on the tip of the moveable ‘finger’. This ‘galea’ produces silk that is used to make silken chambers in which the animals can moult, hibernate or look after their young. Chambers can sometimes be found beneath tree bark. Mating is dangerous, as it is in many predators, and involves keeping away from the female or seducing her, as she may think a prospective mate is potentially a nice meal. So, no direct sexual contact! Sperm are transferred to the female ‘indirectly’ and often at a distance, even in the absence of the male. He produces a short silken structure called the spermatophore that he deposits on the ground and atop of which is a packet of encysted sperm which the female picks up with her genitalia. She may randomly find one or smell it out, or be directed on to it by the male. A few species perform a mating dance like scorpions do, with the male grasping the female’s palps (neutralising them thus avoiding being eaten).

An examination of the underside of the abdomen can determine the sex of an individual, males usually having a more complex and distinctive genital area than females. The female’s genitalia are designed to pick up the sperm, store it and produce fertile eggs. Young do not have distinct genital areas. Some species fertilise their eggs soon after mating whilst others store the sperm for future use. By storing sperm these species can exploit temporary habitats like a rotting log, compost heap or birds’ nest allowing a single female with eggs and sperm to start a new population. Eggs are not laid but glued together and attached to the female's genital opening and hatch as protonymphs which also remain attached and are fed with ‘milk’ produced by the mother’s ovary. The protonymphs grow and moult into deutonymphs, then moult again into tritonymphs and finally into adults. Some protonymphs are free living others remain in the silken chamber with their mother and hence they have never been seen in the wild.

To move around they just walk, but those living in transient habitats ‘hitch-hike’ - they attach themselves to flies, beetles, parasitic wasps and harvestmen and get a lift to a new habitat which may be miles away, a process known as phoresy.

To find pseudoscorpions start by getting some woodland leaf litter, spread it out it over a white sheet or tray and wait and wait ... Pseudoscorpions defend themselves from disturbance by ‘lying low’. They will usually start to move when all the other invertebrates have run off the sheet and you have decided to start again with another load of leaves! When they do appear if you gently touch the front of them you will see a defence reaction: they have a very fast reverse gear! Once spotted make a clear, no-man’s-land area, around the individual so it can be easily tracked and use a fine lightly moistened paint brush (or a small blade of licked grass) or ‘pooter’ to pick them up. For the better equipped enthusiast pseudoscorpions can be found more efficiently using a variety of standard invertebrate techniques e.g. Tullgren funnel and D-vac (a very fine collecting bag is needed as the species are tiny; relatively cheap electric garden blowers are ideal). You can view them with a x20 hand-lens and with luck be able to identify some of the commoner species. However, it is virtually impossible to identify many without the use of a binocular microscope, and in some cases even a compound microscope may be needed. Getting the lighting right will greatly improve the chance of seeing some of the features, especially the various hairs and bristles that distinguish some species. A useful guide is produced by the Field Studies Council: Pseudoscorpions, which covers 27 species; the 28th has only (2020 in press) been recently recognised - others may still be out there to discover. You can submit images and request for help to the recording group (see www.chelifer.com) or the British Arachnological Society and there is a useful Facebook page too.

Pseudoscorpions can be searched for from February onward. When it is very cold, some species will vertically migrate down in the soil or into rotting wood etc. but when the weather is mild they are less likely to do so. The Sussex Biodiversity Record Centre has very few Pseudoscorpion records in the database and new ones would be very welcome. If you do find Pseudoscorpions, please send your records (with photos) to bobforeman@sussexwt.org.uk and they will be passed to the national recording scheme or, alternatively upload them to iRecord.

Gerald Legg

 

 

January: Two epiphytic liverworts

Frullania dilatata

Frullania dilatata (top) and map showing distribution of records below.
Photo: Brad Scott

Metzgeria furcata

Metzgeria furcata (top) and map showing distribution of records below.
Photomicrograph: Brad Scott

Circular patch of Frullania dilatata

Circular patch of Frullania dilatata on tree trunk.
Photo: Sue Rubinstein

Frullania_dilatata Drawing S. Rubinstein

Frullania dilatata: Dilated Scalewort, structure and detail of leaf cells.
Drawing: Sue Rubinstein

Metzgeria furcata Drawing S. Rubinstein

Metzgeria furcata: Forked Veilwort, structure and detail of thallus.
Drawing: Sue Rubinstein

When you are out and about, do have a look for some common liverworts on trees. There are two which are especially common and are likely to be in every part of Sussex. So far they have only been recorded in about half the county, and the maps are consequently more of an indication of the distribution of bryologists than the plants, so all new records are valuable.

Frullania dilatata is very distinctive, and is brown or green, often observed in neat round patches on a wide range of deciduous tree trunks. Its leaf lobes are very round and only about 1mm across.

Metzgeria furcata is also quite distinct, though there are two similar species. It is green and is forked and flat, with a strong midrib, and often found growing with Frullania dilatata. It looks like little green ribbons about 1mm wide. The two similar (though less common) species are Metzgeria violacea and Metzgeria consanguinea; they both have little granules (gemmae) either at their tips or along their margins, respectively.

We want to see how many records we can receive by the end of February, and especially how many new tetrad records there will be, so please have a look at your local trees. Please submit any records with some photos to iRecord, or with location, grid reference and date to @Trichocolea on Twitter, or by email to sue@rubinstein.plus.com.

There are regular field meetings recording the mosses and liverworts of the area organised by the South-East Group of the British Bryological Society, to which all are welcome, and you are encouraged to sign up to our email list. You can also follow the bryophyte recording activity in the county on our blog: https://sussexbryophytes.wordpress.com/bbs-se-group/.