Lovely little loofahs

As I have a static page devoted to dead wood monitoring at habitat/woodland scale, the organisms associated with dead wood do appear on my blog from time to time. On this occasion, I'd been tidying up the 'wrecking yard' at the far end of our garden where I cut firewood and so on. Because of this, unwanted offcuts that are too decayed to be useful have been piled up to form habitat for saproxylic (dead wood) species. Often these may be small invertebrates such as beetles and barklice, but of course, Fungi are also important in the decay process, as are myxomycetes (slime moulds) which, although often included as 'honorary Fungi', are actually Protozoa. As a group, 'myxos' are widespread - everywhere which some suitable substrate, though they often remain unseen as their fruiting bodies are often very short-lived. So, I was interested to see some clusters of small loofah-shaped growths on small rotting logs.

The myxomycete Arcyria obvelata - approx 1cm tall

Having a copy of Ing (1999) made identification pretty straightforward - Arcyria obvelata is a common species on dead wood, especially beech, sometimes oak, and occasionally (as here) on conifers. It is typified by the short stalk leading to a funnel-shaped cup upon which there is the tall, pale yellow sporangium of tangled tubes bearing minute spores, the whole being up to 15mm tall. When newly grown, the sporangium is a short, smooth cylinder, but when mature it expands as seen here with the longer ones drooping.

Apparently there are some colour variations, but these have not yet been found in Britain - maybe something to look out for!

A larger clump of Arcyria obvelata

Reference

Ing, B. (1999). The Myxomycetes of Britain and Ireland: An Identification Handbook. Richmond, Slough.

Uninvited guests in the nest

Having recently described the unexpected discovery of an occupied song thrush nest and the subsequent successful fledging of the chicks, being a bug-nerd at heart, I felt the need to have a closer look at the nest itself once it was no longer in use to see if any small invertebrates lay within... However, this isn't just random nosiness - there are many parasites that live in the nests of birds and mammals, and it's also the type of place where overlooked species may be found - after all, not that many people are likely to check. So, white tray in hand I began to sift...

The first species to popout was a barklouse or psocid (Psocoptera). This group contains many small species that are associated with bark, dry plant material and so on. I won't go into too much detail here, but the specimen was about 1.5 - 2mm long, variably brown with yellow and brown markings on the head, and the wings held like a shallow roof over the abdomen. Helpfully (as these tiny creatures can be tricky), the forewings also had a pattern of spots that indicated the genus Ectopsocus. As it happens, this pattern is quite strongly diagnostic and as you can see below, the spots are at the end of the wing veins and extend along them so are about twice as long as wide. This provides an identification as E. petersi - an interesting find as it is probably under-recorded, having previously been placed in the 'E. briggsi' group of similar species. However, if any psocid specialists are aware of further taxonomic changes, please do let me know.

Forewing of Ectopsocus petersi

The second species was about the same size (1.5 - 2mm), but quite different in structure - as well as the prominent bristles, it also had a relatively large ventral spring joined to the rear of the abdomen - clearly a springtail (Collembola).The blue-grey colour, which I admit was clearer in the specimen than the photos below), and other features of the ocelli, bristles and spring, plus a dark spot between the antennal bases, suggest that it is Entomobrya lanuginosa (E. myrmecophilus is associated with ants, rare and with longer bristles, while Willowsia have leaf-shaped scales rather than the covering of bristles). This is usually coastal, but inland sites are known, and a bird nest seems perfectly reasonable for a species that can be found in dry, sheltered locations.

Entomobrya lanuginosa

Close-up of Entomobrya lanuginosa

So, an urge to investigate, and a bit of work, turned up a couple of unexpected species. Possibly not as immediately engaging as nestlings becoming fledgelings (though, my bug-nerdiness means I do like them pretty much equally), but as always, species records are valuable, especially for under-recorded taxa.

References

Hopkin, S.P. (2007). A Key to the Collembola (Springtails) of Britain and Ireland. FSC, Shrewsbury. The current standard work for UK species - excellent.
New, T.R. (2005). Psocids: Psocoptera (booklice and barklice) (2nd ed.). Handbooks for the Identification of British Insects 1(7): i-iv, 1-146. Also the current standard work for UK species - also excellent.

The spread of the trident

Most of us are used to finding spiders indoors, but harvestmen (which are arachnids but not spiders) tend not to enter buildings quite so readily. However, for the last few days, one has taken up residence in the toilet-roll stack in our bathroom, so (as is often the case when an invertebrate grabs my attention), I decided to look a little more closely.

Harvestman on a toilet roll; body length approx 8mm

As there are several similar species of harvestman in Britain and this wasn't one of the more obviously distinctive ones, I headed to my bookshelves to consult Hillyard (2005), the standard work on the subject. However, the start of the key involves looking closely at the pedipalps (shorter leg-like appendages at the front - they have mainly sensory, and partly feeding-related functions) but I didn't want to capture the specimen on this occasion. Instead I decided that a photo would have to do and that I would see if an identification could be made on the balance of features. This is what I noted (see below for photos illustrating some of these points):

• The central stripe or 'saddle' is clearly outlines in black and paler in the middle, and its rear margin is cut off in a straight line.
• The legs are relatively short and robust (for a harvestman) unlike the longer and more spindly legs of genera such as Leiobunum. The femora are more or less cylindrical, while the tibiae and patellae are more angular in cross-section.
• The ocularium (eye-bearing structure, indicated by a blue arrow) is relatively small, has small bumps or 'tubercles' on top and is about twice its own length from the from edge of the cephalothorax.
• The trident (red arrow) is titled slightly upwards with the prongs diverging slightly and not especially different in length (the central one is a little longer, but starts further forward so the actual lengths are very similar).
• There is a paler line widening forward from the ocularium to the trident (outlined by green dashes).
• The sides of the cephalothorax bear small, variable prongs and protuberances (green circles).

Along with the indoor/building-related location, these features combine to indicate that this is Odiellus spinosus. There are a number of superficially similar species, but these do not have the same combination of spines/tubercles and leg features etc.while Mitopus morio does not have a trident.

Features associated with the cepahlothorax of Odiellus spinosus

Leg segments of Odiellus spinosus. (1) femur, (2) patella, (3) tibia, (4) metatarsus, (5) tarsus

Although known from Britain since the middle of the 19th century (it is found from northern Spain to the Balkans in continental Europe), this is a species that has recently been spreading northwards through Britain, having reached at least as far as Cumbria. It is probably that this is another of the many invertebrates whose range is expanding with the warming due to climate change - as it avoids high ground in its continental range, it is likely that temperature is a key controlling factor. So, if you do see one of these, and you are sure what it is, why not help map its changing distribution by sending the details to your local Biological Records Centre.

References

For a cheaper option than Hillyard's 2005 work, Richard's 2010 fold-out guide is also a very useful starting point for a few pounds.

Hillyard, P.D. (2005). Harvestmen (3rd ed.). FSC, Shrewsbury.
Richards, P. (2010). Guide to Harvestmen of the British Isles. FSC, Shrewsbury. [laminated fold-out card]

Chicks are best in a well-dressed nest

A few months ago, I built a new riddling table (essentially a mobile soil sieve on legs) for our local community farm - the soil is very stony and it's a good way of making a fine tilth or lump-free compost. It wasn't going to be needed much over winter, so was stored under some polythene sheeting and next to a thick hedgerow to keep the weather off until required. However, when the cover was removed a few weeks ago, there was a surprise - a bird's nest complete with four pale blue, slightly speckly eggs. The cover was quickly replaced and a notice sent round to let everyone know that the table couldn't used for a while. Even without looking at the eggs it was clear that it belonged to a pair of song thrushes (Turdus philomelos) as the parents could soon be seen attending it. A week or two later, I revisited the nest to check its progress.

Song thrush nest with 3 nestlings

As you can see, there were 3 nestlings - still bald with their eyes closed. The nest is on a shallowly sloping  wooden platform (used to funnel sieved soil into a wheelbarrow) underneath the sieving tray - you can see one of its wheels at the back - with the whole structure covered in polythene - an excellent hideaway. Song thrushes usually build their nests in trees and shrubs, typically near the trunk around 1-4m up, though they can sometimes be found in buildings, on the ground, on stumps and fallen branches or in hollows among creepers. Whatever the precise location, they tend to be in shady, well-hidden places in or near woodland or hedgerows, and this artificial construction suited their needs very well.

Song thrush nestlings - some downiness has already appeared with a few feather shafts just beginning to develop

These were the only photos I took as I didn't want to visit the nest for longer than required to obtain enough information to make a useful record. Such records, if obtained carefully, provide valuable information about the breeding success of many species and in the UK, the BTO's Nest Record Scheme uses volunteers to follow the progress of nests, providing training where required. With the bad old days of egg collecting largely behind us (though some illegal collecting still occurs), a Code of Conduct needs to be followed when recording nests. Much of this is common sense (don't visit more often than necessary, limit the amount of disturbance caused and try to approach the nest when it is unattended) but some aspects are less obvious.

For example, it is widely believed that visiting a nest will increase the probability of the clutch failing. However, reviews of research into nesting success (Götmark 1992, Mayer-Gross et al. 1997) indicate that this is not the case, if the Code of Conduct guidelines are followed. Examples of some other less obvious actions that need to be taken are as follows (for a full list, see the Code):

• In case parent birds are watching, approach nests casually, as if by chance, rather than directly and deliberately - you are then likely to be seen as harmless (like a passing herbivore) rather than a potential nest predator.
• Adults are most sensitive to disturbance at the start of the breeding attempt, during egg laying and very early in the incubation period - it these times, they have invested less energy in the nesting attempt and have more time to lay a replacement clutch.
• Conversely, the parents become less sensitive of disturbance as the nesting attempt continues, but the chicks’ become more aware, and when partially feathered, the young of some species may instinctively scatter from the nest, a process known a ‘exploding’. This is adaptive when a real predator raids a nest is it gives a chance of survival for at least part of the brood, but once out of the nest the chicks are vulnerable to cold and to ground predators. Also, don't forget that chicks can only legally be handled by licensed bird ringers.

Here, the nest was unattended, the adults past the period of maximum senstivity and the chicks still too young to scatter - the perfect time to visit. After this, the adults could be seen bringing food to the nest and all three nestlings were seen to fledge. Once it was clear that the nest was no longer in use (young stay in the nest for 12-16 days), it was removed for closer inspection.

Song thrush nest after the chicks had fledged

The nest, built by the female (though both parents feed the young) is made of a woven circle of small twigs, leaves, grass, roots, moss and string surrounding a smooth cup of papier-mache made from rotten wood-pulp (sometimes mud is used). Close up, it really is an impressive structure - neatly woven and well camouflaged (or would be in a tree), and the inner cup thin, light and neatly smoothed. Although the young are very similar to those of the mistle thrush (T. viscivorus), as are the nests and breeding times, the nest structure is clearly different with the mistle thrush making a bulkier cup of plant material with soil mixed into it and lining it with finer grass.

If you want to know more about how to identify nests, eggs and nestlings, Harrison & Castell's 2002 guide is excellent, but do take care as noted above, and if possible join the Nest Record Scheme; information about breeding success is vital for well-informed conservation.

References

Götmark, F. (1992). The effects of investigator disturbance on nesting birds. Current Ornithology 9: 63-104.
Harrison, C. & Castell, P. (2002). Bird Nests, Eggs and Nestlings of of Britain & Europe with North Africa and the Middle East (rev. ed.). HarperCollins, London.
Mayer-Gross, H., Crick, H.Q.P. & Greenwood, J.J.D. (1997). The effect of observers visiting the nests of passerines: an experimental study. Bird Study 44: 53-65.

Making Solomon's mines

As it seems to be the season for finding fly larvae (for example here and here), I thought I'd continue with this theme, but move from aphid predators to a species feeding on (or rather, in) plant material, in particular, a leaf miner feeding on Solomon's-seal (Polygonatum multiflorum).

Leaf mine in Polygonatum multiflorum - the arrows indicate small groups of feeding larvae

There are few leaf miners of P. multiflorum, and it was clear that these were most likely the larvae of the fly Parallelomma paridis (Diptera: Scathophagidae). However, a closer look was needed for confirmation, and having kept the leaf in a container overnight, the larvae began to leave the mine.

Larva of Parallelomma paridis. The head is to the bottom of the photo (note the black mouthparts) and the pair of posterior respiratory processes (PRPs) can be seen at the rear. Yellow-green gut contents are also visible.

Before looking more closely at the larva and subsequent pupa, it is worth noting that there has been some taxonomic confusion regarding this species. It has been synonymised with P. vittatum, but is now (by some dipterists at least e.g. Nelson, 1990 and Chandler, 1998) considered a separate species with P. vittatum on Orchidaceae (as noted by Smith, 1989) and P. paridis on Liliaceae as here. I take the view of Nelson and Chandler that these are separate species. The genus has also been known as Americina (which, along with the required Latinisation, means that some specimens of this species may be labelled Americina vittata).

The mines of this genus start near the eggs which are laid in small groups with the larvae then feeding communally.

Empty eggs of P. paridis - note the elongate shape and longitudinal ridges. The slit to the right appears to be the entrance to the mine

A small group of P. paridis larvae feeding together in the leaf mine. The arrows indicate the small, black, hooked mouthparts.

The mouthparts are hard 'sclerotised' hooked structures (mouth-hooks) which equate to mandibles and, in some groups of flies, are useful in identification. In this species the overall form is curved with a distinct hook at the tip. They are used to scrape leaf material into the mouth - the group of larvae work more or less in unison, gradually extending the mine as seen in the short video below the next photo.

Close-up of the mouth-hook of P. paridis. As the photo was taken of a live specimen still feeding in the mine, it is a little unclear (the rectangular leaf cell walls are visible), but the approximate outline on the right shows the hooked tip at the bottom of the image.

As well as muscle contractions, movement through the narrow mine is aided by the additional grip created by rings of tiny spikes on the surface of the larva, running around the front edge of each segment.

The head of the P. paridis larva - note the rings of tiny black spikes around the front of each segment. A pair of 'eye-lash' shaped tufts (probably with a sensory function) can also be seen, if a little out of focus, on the first segment.

Pitkin et al. (2012) state that the larvae of P. vittatum (noting the taxonomic confusion mentioned above) develop rapidly, emerging from the mine and pupating outside their food-plant after only 13 days and remaining as pupae for almost a year (around 348 days), with adults emerging in May and June. In fact 5 of the 6 larvae in my sample have already pupated and the other appears to be undergoing this process (see below) and so I expect to be storing the pupae for some time before being able to see the adults.

Pupation, with the associated hardening and darkening of the cuticle, appears to begin with the PRPs and then progress inwards from both ends of the larva. So, I would like to finish with a series of images showing the progress of pupation in this species and some of the structures of the pupa itself.

Larva of P. paridis with the PRPs having darkened as pupation is about to begin.

Larva of P. paridis showing partial pupation.

Pupa of P. paridis (approx 4mm long)

Head of P. paridis pupa showing the 'eye-lash' shaped tufts also seen in the larva above

Rear of P. paridis pupa showing the pair of PRPs and several smaller spines

Rear of P. paridis pupa showing the pair of PRPs and rings of small spikes around the articulations of segments.

Rear of P. paridis pupa showing the pair of PRPs and smaller lateral spines

References

Chandler, P.J. (1998). Checklists of insects of the British Isles (new series) part 1: Diptera. Handbooks for the Identification of British Insects 12(1): i-xx; 1-234.
Nelson, M. (1990). Observations on the biology and status of British dung flies of the genus Parallelomma Becker (Dipt., Scathophagidae). Entomologist's Monthly Magazine 126: 187-189. 
Pitkin, B., Ellis, W., Plant, C. & Edmunds, R. (2012). The Leaf and Stem Mines of British Flies and Other Insects: Parallelomma vittatum (Meigen, 1826) [accessed 05/06/2012].
[Diptera: Scathophagidae]
Smith, K.G.V. (1989). An introduction to the immature stages of British flies. Handbooks for the Identification of British Insects 10(14): 1-280.