A little red underwater planet

 I have brought a few animals from my half barrel (=mini pond) to see close up to a small tank. Most of them are detritus feeders or vegetarians, and regularly I top up the tank with fallen leaves. Today's water was stained red and the reflection of the light in the water and the leaves made the photos take a surreal tint. A Great Pond Snail (Lymnaea palustris) fed on the algae growing on the tank walls (above).

Another snail, Planorbis planorbis

A group of ostracods, small bivalved crustaceans, and a copepod towards the left of the image.

There are also a few water slaters and planarians, but they didn't show as well today.

UPDATE: Thank you to Richard Comont for the pond snail ID, now corrected.

More information
Online aquatic snail identification guide from the Conchological Society. here.

Leaf sleepers

This is a good time of year to search for bugs in the leaf litter. On the top layer, ladybirds are set for the winter in the cosy, dry folds of the fresh fallen leaves. They usually cuddle up close to other ladybirds of the same species to overwinter, but it is not unusual to see two species together, like the 22 spot and 7 spot above. If you search a bit deeper on the soil, you can find centipedes, earthworms, and woodlice. With the colder temperatures, they are more torpid than usual, and then easier to photograph.

A shiny woodlouse, Oniscus asellus

Centipede, Lithobius forficatus

 A group of 22 spot ladybirds inside a vine leaf

Arion sp. slug

7 spot ladybird and birch shieldbug

Freshwater Flatworms

 If you kneel down on the edge of a clear water pond and look towards the bottom, even at this time of year, you might be able to see some flattened elongated creatures slithering over the sediments, like they are levitating (above). They are planarians or flatworms. On closer inspection they have a quizzical look due to their simple eyespots or ocelli, which appear to be both looking inwards. They are relatively simple organisms, which move over a carpet of cilia and have simple guts, with a single opening, the mouth, which is sometimes placed in the middle of the body. I am trying to get some shots of water slaters and I have set up a little tank at home. Most of the time when I get some decaying leaves from my half barrel (=minipond) a few flatworms are accidentally transferred with them, and then I can take some photos of them while they climb on the walls. There appear to be several species, but yet have to find out some resources to tell them apart.

One of the most striking features of flatworms is their capacity for regeneration. If you cut them in half, each half grows the missing parts. Even a tiny part of a planarian can regenerate a complete individual.

Centipede on a walkabout

It is long, I counted 76 pairs of legs! My young daughter spotted this centipede, Stigmatogaster subterranea, walking on a stone wall out in the open. This is the first time I see this behaviour in this otherwise soil and leaf-litter living centipede. When disturbed, it had no trouble walking backwards, which had me puzzled for a bit, as I confused the tail and the head end!

The centipede lifted its head as if sniffing...

 ...and finally disappeared in the leaf litter.

Foggy morning

The fog painted the spider webs hanging from bushes and fences this morning with pearly dew drops. It made evident that at least three spider species are still active. On the photo an Araneus diadematus web, we also saw Zygiella x notata and Linyphia triangularis webs.

Winter bees on Mahonia

A lovely, still sunny day, I walk to a clump of Mahonia on a corner of an avenue. I have posted about this bug magnet in previous years (here, here and here) At this time of the year, Mahonia (Oregon Grape) is on bloom, its sweet scent and profuse, sunny-bright yellow flower spikes attract all late nectar lovers. Today, the bushes were busy, Bluebottles, Drone flies, honeybees and three (!) bumblebee species were feeding on it. A Bombus pratorum queen about to land, with a dronefly on the foreground on the top photo. This is one of the garden plants that are likely to have contributed to favour winter colonies in bumblebees. Bugs love this bush, and so do I. 

Bombus terrestris queen. I have seen a worker this week too.

Bombus hypnorum

Honeybee

Dronefly and bluebottle

Pond Skater

One of my earliest bug memories is watching pond skaters moving effortlessly and magically over the water. Pond Skaters, Gerris sp., also known as Water Striders, are true bugs: they piercing mouthparts are used to suck the juices of the insects they predate. Their legs are clothed with water-repellent hairs and they propel themselves with their middle legs in a flicking glide. Their front legs are small and kept tucked ahead of them, sensing the vibrations in the water from other ponds skaters or potential prey that have fallen in the water, and also grasping and holding their prey. They are seven similar species of Pond Skaters in the U.K., and they are sometimes found in the same pond. Pond skaters are active in these mild days of autumn and will overwinter as adults, moving away from the water with the first frosts. Many pond skaters species are polymorphic and have long-winged and short-winged morphs. In species with two generations per year, the long-winged form tends to be the overwintering generation - which is also the dispersive one - while the summer generation tends to be short winged. When the winter comes, short-winged individuals, unable to fly, will crawl out of the water and hide in the bank, while long-winged ones can fly away from water, to sites that are free from risks of flooding or freezing. In the spring, emerging pond skaters will fly back to ponds and lakes, using the reflections of the water - or other shiny surfaces - as guide.
Pond skaters, as other true bugs, go through five instars before becoming adults. The individual of the top photo is a nymph (24 Jun 2011), the one at the bottom, an adult (2 Jul 2011). Although the photos are from earlier in the year, smaller nymphs were still in a local pond last monday.

The Great Ramshorn Snail

There is still a lot of activity in ponds. We haven't had a frost yet and Pond Snails, water-lice and ponds skaters go about their lives as usual. This is a Great Ramshorn Snail, Planorbarius corneus, inhabitant of still or slow moving waters with a high calcium content and plenty of vegetation. Unlike land snails, Ramshorn Snail's eyes are at the base of their long tentacles. They graze algae and plants or feed on dead leaves. They are hermaphrodite, although they prefer to cross-fertilise one another. They will lay their gelatinous egg batches on the underside of leaves. I photographed it on the white bowl with some rain water.

Is global warming erasing a melanism cline?

 The 2 spot ladybirds, Adalia bipunctata, I find in my garden are of the typical morph, red with 2 black spots, one in the centre of each wing case, but there is also a melanic morph in this species* - black with four red spots - and several rarer intermediate morphs, which are determined genetically. Some colour morphs tend to be more common in some areas than in others. This geographic variation is thought to reflect differences in temperature regulation between morphs. Melanic ladybirds benefit from thermoregulating more effectively in certain microclimates: when there is little, intermittent sunshine and is colder. This advantage becomes most important in early spring, when after emerging from hibernation ladybird behaviour is strongly limited by temperature, so the black ladybirds can start reproducing earlier. Paul Brakefield and Peter de Jong have studied the polymorphism in the two spot ladybird in Holland for 30 years. The two spot colour polymorphism, nicely matched the differences in climate between the warmer coast and the colder inland areas. At the beginning of their study period, in 1980, the dark morph was commonest inland, where it reached 60%, and its frequency decreased gradually towards the coast (less than 20%). Samples taken in the same transect since then show how the sharp decline in frequency of the dark morph gradually disappeared to the point that there was little if no differences between sampled areas in 2004, with the frequency of the melanics in inland areas dropping to similar levels than the frequency in coastal areas. Brakefield and de Jong think that the disappearance of this cline is a response of the ladybirds to the gradually warming climate in the area.

Figure 1 Changes over time in the proportion of the illustrated melanic and non-melanic morphs of the two-spot ladybird beetle along a transect of ca. 115 km in length in the Netherlands (bottom-left). Samples were collected in each of the 5 years indicated at 16 more or less evenly spaced localities from west to east. Colouring of years matches the histograms for melanic frequency in the individual samples from each locality. The panel on the bottom-right shows deviations in average temperature from a ‘normal’ season/year at De Bilt (red spot on map). From left to right, columns represent data for winter (Wi), spring (Sp), summer (Su), autumn (Au) and the overall year (Tot), respectively, and from top to bottom for different years beginning before the period of ladybird sampling. The colour of each block indicates the extent to which the average temperature in the particular season/year deviated from ‘normal’; white, no deviation, blue, cooler than normal (dark blue more extreme than light blue), red, warmer than normal (dark red more extreme than light red)(from Brakefield & de Jong, 2011)

The story has a second dark aspect. The researchers had trouble reaching acceptable sample sizes in the 2004 sampling season. They even failed to find 2 spot ladybirds in two localities where they previously had been abundant. They attribute the decrease in numbers of the 2 spot ladybird to the impact of the invasive harlequin ladybird, which reached Holland in 2002. Not only the melanism cline is gone, but the 2 spot seems to be dissapearing as well.

References

Brakefield PM, & de Jong PW (2011). A steep cline in ladybird melanism has decayed over 25 years: a genetic response to climate change? Heredity PMID: 21792220

*UPDATE
So it seems I do have melanic 2 spots in the garden (above). Thank you to Helen Roy, who curates the Ladybird survey site for the ID.

The Migrant Hawker

The Migrant Hawker, Aeshna mixta, is one of the commonest dragonflies found away from water. It regularly visits my pond-less garden, with a clearly marked peak in the second half of August (the male on the top shot from 15th August this year). This species is a fast developer, their larvae take just a year to become adults, but it is sensitive to the cold. Adults are not territorial and are often found hunting together, at high, patrolling over the garden hawking for insects. Early in the morning they rest hanging from vegetation, sunbathing, at about 1-2 m high, often a pair not far from one another, and they then allow close approach.

A female Migrant Hawker basking, with another individual on the background (16/08/06) - which I only noticed when checking the photos.

Although dragonfly migration has been known for over a century, it is still a little known phenomenon. Several British dragonfly species are regular long-distance migrants, like the Four Spotted Chaser and the Common and Ruddy Darters, and others occasionally appear as vagrants from the Mediterranean or even from North America. Where do they go and why do they do it? Do they migrate back and forth or do they just wander? Is this behaviour to avoid overcrowding or drought, in search for good sites for reproduction? David and Elizabeth Lack (1951) favoured the existence of large scale two way migration in dragonflies, like that of many birds and butterflies, after observing large numbers of Common Darters passing over a high mountain pass in the Pyrenees. American migrants tend to be species breeding in ephemeral or semipermanent ponds, which dry frequently, so migration might also be a wandering in search of suitable ponds. Recently, a combination of miniaturised radio transmitters, isotope analysis and genetic markers have shed light into the migratory behaviour of the American Common Green Darner, Anax junius. Although the Migrant Hawker has been seen forming large swarms, unfortunately, we know very little about the migration in this species. In any case, its migratory behaviour makes it a very good coloniser. In the early 20th century it was regarded as a rare immigrant - in fact it was called Scarce Hawker -, but since an invasion in 1935 it has been steadily and rapidly expanding its range northwards and westwards in the UK, reaching Scotland in 2004. The species also colonised Ireland in 2000 and is now well established. I can't wait to find out more about these fascinating garden visitors.

References
Wikelski, M., Moskowitz, D., Adelman, J., Cochran, J., Wilcove, D., and May, M. (2006). Simple rules guide dragonfly migration Biology Letters, 2 (3), 325-329 DOI: 10.1098/rsbl.2006.0487

Lack, D. and Lack, E. (1951). Migration of Insects and Birds Through a Pyrenean Pass The Journal of Animal Ecology, 20 (1) DOI: 10.2307/1644

E.S. Dyatlova and V.J. Kalkman (2008). Massive migration of Aeshna mixta and Sympetrum meridionale in the Ukrainian Danube delta (Odonata-Anisoptera: Aeschnidae, Libellulidae) Entomologische Berichten, 68, 188-190

Brian Nelson, Colm Ronayne and Robert Thompson (2003). Colonization and Changing Status of Four Odonata Species, Anax imperator, Anax parthenope, Aeshna mixta and Sympetrum fonscolombii, in Ireland 2000-2002 The Irish Naturalists' Journal, 27 (7), 266-272

How to get a snail to go aaaaah!

I have spent quite a lot of time lately tidying up my photo library and tagging photos and I have come across several worth posting about even if they won't be as timely as usual. I wanted to see if I could take some shots of snail's mouths. To do this, I mashed up a few dandelion leaves and painted an area of the outside of one of the conservatory window with the resulting concoction. Then I found a few active snails and this one delivered. It started climbing up the window, its foot showing the muscular ripples that power its slow advance, mouth shut tight.

As soon as the snail felt the dandelion mixture, it opened its mouth and started licking it, showing its tongue (the radula) and the chininous, dark hardened ridge in front of it. The radula is a muscular organ covered in rows of hard little teeth that can scrape surfaces and it was very evident how the snail used it to eat the bits of the dandelion leaves once it got to them.

Dandelion leaves, yum!

These are the marks left by snails or slugs while grazing algae growing on a pot

The snail also showed nicely the opening of its lung, on the right side of its body.

A wrapped up genetic legacy

There are still fresh garden spider webs around if you look, with large Araneus diadematus females making the best of the mild weather. Many, though, have now died, exhausted and shriveled up, after laying eggs. This genetic legacy to next year generation is now inside wrapped up in a yellow silken cocoon attached a corner sheltered from the rain. After finishing their cocoon, they sit on it until they died, not bothering to make a web any more. The eggs will overwinter inside the sac and the spiderlings will emerge the next spring.

30 October 2011, female spider on her egg sac.

Autumn colours

This moth caterpillar was ready for the winter when I disturbed it. I used a cherry leaf as a background. The garden spider below had hung her web in front of the rowan, so I could take advantage of a clump of berries as background.

The face of the alien aphid muncher

This Harlequin ladybird happily eating an aphid on the 6th of November illustrates how active many of these ladybirds still are. I found young and old larvae, pupae, mating adults and also dormant adults in a small area near in my local park. Harlequins are multivoltine, and will carry on reproducing as far as conditions are suitable. In northern Europe, two generations and possibly three if weather conditions allow can occur, as adults do not need to enter dormancy before they can reproduce, as it is the case with the 7 spot ladybird.

Little riders on the wind

The mass influx events of Painted Ladies - such as during the summer of 2009 - and wildlife documentaries on the Monarch Butterfly have made butterfly migration familiar to everybody. Many butterfly species are now known to carry out bidirectional migrations, for those of the northern hemisphere, towards the north in the spring and towards the south in the autumn. Surprisingly, the extent of fascinating behaviour was only recognised relatively recently. Up to the 1930s, the only butterfly that was acknowledged to migrate was the American Monarch, Danaus plexippus, with evidence for migration in other species dismissed even from experienced entomologists and lepideropterists as "overflow": one way dispersal movements from successful, very dense populations. One early researcher was set to change matters: Carrington Bonsor Williams (widely known as C.B.), from Rothamsted Experimental Station in the U.K. He was passionate about insect migration and amassed large amounts of data on the subject, in Britain and abroad. In his 1930 book Migration of Butterflies and later work, he presented evidence for migration for over 200 species of butterflies worldwide, including support for return migration. He also helped organise the collation of data collected by naturalists across the U.K. on insect migration. His analyses of these data gave strong evidence for migration for six species of British butterflies: the Painted Lady, Small Tortoiseshell- which also hibernates in the U.K. - , Red Admiral, Large White, Clouded Yellow and Pale Clouded Yellow. For the Red Admiral, the records  showed clearly a dominant proportion of individuals flying in a northerly direction up to the end of July, and a southerly direction during September and October:

(Figure from Williams 1951)

In the case of the Painted Lady and the Large White, the lack of evidence for a return migration puzzled Williams:

I have already (Williams et al. I942, p. 250) pointed out the difficulty of accounting for the persistence of a habit of movement in one direction only on any theory of evolution. If we accept that directional movement in butterflies is simply an overflow from an over-populated area, and that none of the emigrants ever return; then the species must be perpetuated by the offspring of those individuals which do not emigrate. Thus a habit must persist for countless generations, in spite of the fact that all  individuals which develop it die without contributing to the continuity of the species.

He was optimistic though, and correctly predicted that return flights would be found in all species once enough research effort was put into it, making butterfly migration as important a phenomenon as that in birds. Indeed, recent research - some of it carried out in Rothamsted - including meteorological analysis of prevailing winds when influxes of Painted Ladies occur, and entomological radar research has shown that the Painted Lady taked advantage of tailwinds as a migratory aid and that the reason that these flights were not detected is that they fly at high altitude.
 Migrating butterflies are tracking suitable breeding grounds, areas where larval food plants are abundant. Red Admiral caterpillars feed on fresh, rapidly growing nettles. At the end of spring, nettles start to wither in the Mediterranean winter grounds, so the spring Red Admiral adult generation flies to Northern Europe - and also up mountains - where nettles are luscious. They mate and lay eggs in the north and the resulting autumn generation of adults migrates due south in the autumn.

(Figure from Mikkola 2003)
Unlike birds, butterflies breed both in the winter and summer grounds, and also unlike birds, each generation makes a one way trip, leaving the return journey to their offspring.
(Photo above, a fresh, autumn generation Red Admiral feeding on Cherry Laurel, 19 Aug 2011)

References
Williams, C. (1951). Seasonal Changes in Flight Direction of Migrant Butterflies in the British Isles The Journal of Animal Ecology, 20 (2) DOI: 10.2307/1537

Kauri Mikkola (2003). The red admiral butterfly (Vanessa atalanta) is a true seasonal migrant: an evolutionary puzzle resolved? European Journal of Entomology, 100, 625-626


Stefanescu, C., Alarcon, M., & Àvila, A. (2007). Migration of the painted lady butterfly, Vanessa cardui, to north-eastern Spain is aided by African wind currents Journal of Animal Ecology, 76 (5), 888-898 DOI: 10.1111/j.1365-2656.2007.01262.x

Chapman, J., Nesbit, R., Burgin, L., Reynolds, D., Smith, A., Middleton, D., & Hill, J. (2010). Flight Orientation Behaviors Promote Optimal Migration Trajectories in High-Flying Insects Science, 327 (5966), 682-685 DOI: 10.1126/science.1182990

A november gift

Each passing day is shorter and with a weaker sun than the previous one, and each Red Admiral sighting feels like a lovely gift. This afternoon, a battered individual sat basking on the fence, cleaning its head, with its body and wide open wings angled, casting a long shadow, capturing the maximum warmth of the sun. After a few minutes, it fluttered to the Erysimum and fed on it. For a while, it alternated feeding - later on the flowers already in the shade - and warming.

The maladapted parasite

There is a corner in my local park which is always teeming with Harlequins. At this time of the year adults ready to hibernate and grown larvae about to pupate dot the railings and fenceposts. A couple of days ago I came across this individual dragging a strange large lump behind as it sluggishly walked on top of a railing. I took a photo and wondered if it was a parasite. Parasites in Harlequins are very interesting, as, this ladybird being an invasite species, they might be adapting to the newcomer and helping keeping this species in check. Richard Comont, from the Centre for Ecology and Hydrology in Wallingford, after checking the photo commented:

It looks like a Dinocampus which has got caught up in the ladybird's wings - I think you can just about see some segmentation at the bottom of the yellow lump. Dinocampus seem to be a bit disorientated in Harlequins - they seem less able to fully paralyse the adults on the way out - so possibly might sometimes emerge from the top of the abdomen, from between the tergites rather than the sternites, which could result in the emerging larva ending up in the wing like this.
Dinocampus, on emerging, usually parasitise their host ladybird, cutting the nerves connecting the legs to the nervous system, and potentially also the tendons of the leg abductor muscles which allow the ladybird to move its legs away from its body (so that when the parasitoid's cocoon is spun between the ladybird's legs it can only be clutched tighter). However, Harlequins with Dinocampus are often not fully paralysed, and instead stumble around slowly, almost drunkenly.

It appears that some native ladybird parasites are also attempting to parasitize the newcomer invasive Harlequin, which is encouraging. Evolutionary success for parasites in expanding their host range to include Harlequins however, will only come if the parasite is successful completing its life cycle in the new host. The offspring of the parasite must actually be able to become a successfully reproducing individual in the new host, and the disorientation of the Dinocampus in Harlequins, which could often result in their larvae being unable to spin its cocoon under the host - which is walking around dragging it - suggests that their success in surviving and actually becoming an adult parasite might still be far lower than in the native ladybirds. They still might have some way to go.

I am most grateful to Richard Comont for allowing me to reproduce his comments in this post and to Lori Lawson Handley for kindly forwarding my photo to some knowledgeable ladybird experts.

UPDATE
From an e-mail from Richard Comont (15/11/11):

I’ve found a couple of these ‘parasitised’ Harlequins today – and the ‘parasite’ was just a pool of reflex blood, which the wing had folded around into a kind of bag – no evidence of parasitism at all!

That's science for you!