Tree-moth mystery solved

After much musing about whether I had found Stigmella suberivora on the non-native cork oak Quercus suber, a discussion on iSpot followed by a little extra microscope work shows it to be Phyllonorycter messaniella. The identification was finally confirmed by looking at the intersegmental spines which are particularly long in the pupa of this species.

The long intersegmental spines which are diagnostic for the pupa of Phyllonorycter messaniella.

This is a widespread species in the UK on evergreen oak Q. ilex and various deciduous oaks, as well as some other tree genera (Heath & Emmet, 1985). However neither this book nor the excellent leaf-miner websites here and here give Q. suber as a host for the moth in the UK. The next job is to find out whether it really is a new host for the moth in this country... update when I know more.

Reference

Heath, J. & Emmet, A.M. (eds.) (1985). The Moths and Butterflies of Great Britain and Ireland. Volume 2: Cossidae - Heliodinidae. Harley, Colchester.

More on the tree-moth combo

A few weeks ago, I posted about leaf-mines on cork oak (Quercus suber) and whether I had found the first British record of the moth Stigmella suberivora on this tree species (it is known from Q. ilex in Britain and Q. suber in continental Europe). Although the mine appeared correct, this is not enough to confirm the record, so I revisited the tree and collected a couple of leaves with occupied mines in order to, hopefully, raise adults which can be positively identified. This is a somewhat uncertain activity but the pupae I collected are being kept in suitably (but not too) moist/humid conditions and, as I write, are definitely still alive.

I have added a couple of images of the pupae, though I have noticed that whereas adults, and to a lesser extent eggs and larvae can be found figured in various publications, reference images of pupae are difficult-to-impossible to find, even on the excellent UK Moths site. So, here they are - fingers crossed that my next post on this topic will cover the final identification!

Unidentified pupa from a Q. suber leaf mine - approx 4mm long - note the mobile abdomen.

Unidentified pupa from a Q. suber leaf mine - head to the left, approx 4mm long, note ventral thoracic hooks and the wings dorsally (beneath in this photo).

Pondnet diary day 1

Pondnet is a new Pond Conservation volunteer survey aiming to identify trends in pond quality and associated species. I was recently allocated a pond in Milkmead Copse in Hampshire's Itchen Valley Country Park, and now spring's arrived, I decided that today was a good opportunity to make my first visit to the site.

The pond in Milkmead Copse

It was good to see some frogspawn had survived the cold conditions as there were at least a couple of hundred recently hatched tadpoles, plus one adult newt. However, something else (yup, an invertebrate) caught my eye - a water scorpion (Nepa cinerea) that came to the surface.

Water scorpion, Nepa cinerea

This is a predatory true bug (Hemiptera) and the raptorial (hunting) front legs used to grip prey are clearly visible, plus the breathing tube at the rear. Although this appears to be a single thin tube, it is actually formed from two halves (they separate if a specimen is dried) - air flows from it along two grooves which have small water-repellent hairs and the spiracles open into these grooves (Denton, 2007). Being a bug, it has piercing/sucking mouthparts rather than the jaws/mandibles seen in beetles. It is a large insect by UK standards at around 20mm in length, excluding appendages. It is an active hunter, taking small fish and various other invertebrates. However, I was surprised to see it tackle a larger (approx 25mm) dragonfly nymph, itself an active and powerful predator.

N. cinerea attacking a dragonfly numph.

N. cinerea on the back of the dragonfly nymph

This is not behaviour I've seen before and the nymph struggled for a few minutes before managing to dislodge its attacker by dragging it against a piece of vegetation. Presumably the position of N. cinerea allowed it to pierce the nymph while remaining out of direct reach. Certainly, the water scorpion swam away after this encounter and the nymph came back to the surface. I'm not 100% sure which species it is as it is coated in silt which obscures key features. However, the size, head shape and silty coating are typical of the black-tailed skimmer (Orthetrum cancellatum) so that is my identification for now.

Dragonfly nymph, possibly Orthetrum cancellatum, the black-tailed skimmer. Note the hairs on the legs and body, coated in silt.

The same dragonfly nymph - note the protruding eyes and the 'mask' showing the mandibles.

So, an interesting start to a new survey programme. More to come from the pond!


Reference

Denton, J. (2007). Water Bugs and Water Beetles of Surrey. SWT, Pirbright.

I really love those phasmid feet

I've written about by pet Macleay's Spectre stick-insects (Extatosoma tiaratum) before, including moulting and images of cast skins, but had never taken a really close look. Having watched even large, heavy adult females clinging to the near-vertical smooth sides of one of my vivaria, I was interested in looking at the structure of their tarsi ('feet'). So, when a shed skin was left intact (the final moult of a female), rather than being eaten as they often are, it was rescued and taken to the microscope.

Tarsal segments - each has a pad or 'euplantula' (indicated by green lines), the final segment having a larger pad ('arolium') indicated by the red arrow, plus a pair of claws. The spiny segment top-right is the end of the tibia.

If you are familiar with these insects, you'll know how sharp their claws are and how good they are at hooking onto any tiny irregularity in whatever surface they are on. A closer look shows one reason why.

The final tarsal segment showing the claws and arolium

Side view of tarsal claw showing the hardened tip

Hardened and narrowed tip of a tarsal claw

 These photos show not only the hooked shape of the claws, but also that the hardened tip narrows to an even sharper point that can poke into the tiniest of crevices for grip, and undoubtedly pierce soft materials just enough to hold on. These structures also bear small bristles and so also have a sensory function - useful when moving about at night and feeling around in foliage. However, I doubt that the claws are the only gripping devices at work here. It is now well known that geckos' feet have a nano-structure that increases surface area hugely and allows them to adhere to smooth surfaces such as glass through van der Waals interactions with the substrate (Autumn et al. 2002). Given that the arolium can be seen to have an irregular, wrinkled surface at even the low magnification above (x40), it is worth zooming in a little more.

Two pairs of adhesive tarsal pads ('euplantulae') showing the wrinkled surface.

Close-up of one euplantula - the wrinkled surface is more clearly visible.

Upper surface of the arolium - slightly granular but not wrinkled, and bearing numerous bristles.

Lower surface of the arolium - finely wrinkled like the euplantulae, and bearing very few very small bristles.

These images suggest a sensory function for the upper surface of the arolium - the lower surface and the euplantulae are more-or-less bristle-free, and their wrinkled surfaces imply a structure that aids grip through increased surface area. Although I do not have access to a higher-powered (i.e. electron) microscope, others do and some species have been investigated further, with Bußhardt et al. (2012) describing, comparing and imaging the euplantae of Cuniculina impigra and Carausius morosus. Essentially they found that "smooth pads are specialized for rather smooth substrates, whereas nubby pads are better adapted to generate stronger forces on a broader range of surfaces". I will investigate further, but as far as I can tell, no-one has done equivalent work for E. tiaratum and I hypothesise that (at smaller scales than seen here) the pads are neither smooth nor nubby (small-bumpy), but instead are wrinkled, mostly longitudinally, which should generate adhesive forces on rough and smooth substrates, but not equally in all directions. Whether I will get to test this hypothesis is another matter!

References

Autumn, K., Sitti, M., Liang, Y.A., Peattie, A.M., Hansen, W.R., Sponberg, S., Kenny, T.W., Fearing, R., Israelachvili, J.N. & Full, R.J. (2002). Evidence for van der Waals adhesion in gecko setae. Proceedings of the National Academy of Sciences of the United States of America  99(19): 12252-12256.

Bußhard, P., Wolf, H. & Gorb, S.N. (2012). Adhesive and frictional properties of tarsal attachment pads in two species of stick insects (Phasmatodea) with smooth and nubby euplantulae. Zoology 115(3): 135-141.

Ye olde bee log

A couple of years ago (how time flies...) I wrote about the diversity of bees in our garden, including an image of Osmia rufa (the red mason bee) using a log that I had attached to our garden fence. Since then, I've made a rather more sophisticated insect hotel including new bee-blocks and have been following the development of bee diversity in our garden as the various features mature and are added to. In the meantime, the old log had become very rotten with little activity noted around it last summer, and so I decided it was time to take it down and see what was inside.

Old bee-log showing extensive fungal decay and woodworm activity.

The outsides had been heavily arracked by woodworm and many holes and crevices had suffered fungal decay with tufts of white mould clearly visible. Onto the deadwood pile with those bits... Splitting the core open provided more interesting features however.

Empty O. rufa cocoons, one in situ in the hole drilled when making the bee-log, the other removed to show the thin papery texture.

The remains of the walls/plus separating cells which are arranged in sequence along a hole.

A view through two O. rufa cocoons - because they are arranged along a hole, the outermost one must leave first, the next then passing through its cocoon to emerge.

The remains of a cocoon including frass (insect faeces), presuambly from the insect before the cocoon was formed.

These are simple enough observations but rarely seen as logs need to be split open to view them - this is of course destructive and is only being done here because the log was past its 'sell by' date given the amount of decay and lack of activity last year. The life cycle of O. rufa is well documented (e.g. here) so rather than repeat this, I simply want to show which aspects of it are readily visible with a little careful effort. For example, although not photographed, a number of holes contained mouldy yellowish masses - pollen stores created by females for their young, but which were uneaten and subsequently began to decay, presumably as the young did not develop for whatever reason (it was a cold, wet summer in 2012 which can not have helped). Others showed mere traces of pollen storage, suggesting successful emergence. Also, as holes in logs are useful shelter for other species, it wasn't too surprising to find evidence of use by insects other than O. rufa.

Smaller pupal cases inside the bee log

One of these non-Osmia rufa pupal cases removed and magnified, approx 6mm long. The red line follows the split where the insect (whatever it may be) emerged; the green arrows indicate a pair of short posterior processes (breathing tubes) typical of many fly pupae.

Beyond determining that it is a fly, I can tell no more about this species - it might be parasitic, it might simply be using a handy hole for pupation with no other link to O. rufa. However, among the various debris and evidence of O. rufa long since left, I did find one intact bee cocoon.

The one remaining O. rufa cocoon, approx 11mm long blocked in by a number of soil and wood particles.

A small female O. rufa emerging from the cocoon.

The small 'prongs' or 'tampers' (one indicated by a red arrow) on the face of the female O. rufa, used to push mud into place when sealing a hole, although they are under-developed in this specimen.

I must say I was surprised to find an intact cocoon and initially thought it was one that had failed to emerge last year. However, in the warmth of my study I noticed some movement and a bee began to emerge. Its movements were rather feeble so a helping hand (well, pin) was used to pull off part of the cocoon. The female that emerged did not move strongly and was very small with (to me) under-developed facial prongs - possibly a poorly developed specimen from last year's poor summer which had managed to hibernate successfully. She has now been released on the bee-hotel - hopefully there will be a emergence of plenty more from the many plugged holes in the newer logs.

The Lawn Shrimp cometh

I quite often receive invertebrates in the post, but they are usually leaf beetles (Chrysomelidae) sent to me for identification/verification in my capacity as organiser of the UK's Chrysomelid Recording Scheme - like here for example. However, a couple of days ago I came home to find something quite different awaiting me on the doormat - a crustacean looking like a small shrimp, or to be more precise an amphipod of the family Talitridae (a group usually associated with seashore habitats rather than inland terrestrial ones).

In this case, it had already been identified as Arcitalitrus dorrieni, the 'landhopper', 'woodhopper' or 'lawn shrimp' by the finder/sender, Dennis Trunecka of the Southampton Natural History Society. This is an interesting find as it is Australian in origin (New South Wales & Southern Queensland), with the first UK record being from the Scilly Isles in 1924. Since then, it has been found in a number of sites across southern England, and also in Ireland, the Channel Isles, west Wales and western Scotland (coastal when north of southern England). However, it is not entirely clear how widely it has established itself in the last couple of decades, although individuals can move tens of metres per day as well as being moved over longer distances by the plant trade etc. (Cowling et al. 2004).

Arcitalitrus dorrieni found in woodland leaf litter in Hampshire. The seven segments of the peraeon and the three segments of the pleon are indicated. Length (head to rear of body in this curved position) approx. 6.5mm.

It is most often found under stones and dead wood or among damp material (detritus, debris, leaf litter) in gardens, damp scrub and woodland. It most likely arrived (and to some extent spread) in the UK through the transport of plants/soil to and between plant nurseries and garden centres. It is uncertain whether this non-native species has a significant ecological impact in the UK, although it is possible that it competes with (and maybe replaces) native detritivores in woodlands. In some locations, it can be found in high densities - up to approximately 2,500 per square metre in Dicksonia antartica litter on the Scilly Isles (Richardson 1980). It certainly can be a significant detritivore, consuming 24.7% of annual litter fall in a coniferous woodland in Ireland (O'Hanlon & Bolger 1999) - more than any of the native macrofaunal species.

Identification is fairly straightforward, especially given the small number of possible confusion species. Orchestia cavimana  is an introduced semi-terrestrial Mediterranean amphipod (Konopacka et al. 2009) but much paler in colour - A. dorrieni is variably dark, and orange when dead as here, though pale if preserved). However, there is another introduced terrestrial amphipod, A. sylvaticus, although this is much rarer in the UK. Using the key in Peart & Lowry (2006), the two species can be separated by looking at the epimera (the three segments of the pleon, singular 'epimeron'). In A. dorrieni, the 2nd epimeron is longer than the 3rd while in A. sylvaticus they are more-or-less equal. In the top photo, this is unclear as the rear edge of eipermon 3 is obscured by one of the legs, but with some legs (re)moved, it is clear that this is A. dorrieni. There are other features which might be required to separate further species but these do not (yet) occur in the UK, although it is possible they could be imported with plants.

A. dorrieni - from the green lines, it is clear that epimeron 2 is longer than epimeron 3.

The head bears numerous appendages including two pairs of antennae (typical of crustaceans) and a complex array of mouthparts - I won't go into the details here but there are plenty of resources online and in print providing introductions to crustacean anatomy. The lateral compression is clear (flattened side-to-side) and is generally a good way of separating amphipods from isopods (e.g. woodlice which are flattened top-to-bottom i.e. dorso-ventrally). The antennae are inserted in front of the eye which is black and not especially well developed, being covered by a transparent plate. This is likely to be an adaptation to its life within/under leaf-litter and under damp material where vision is less likely to be useful than senses such as touch - note the long antennae and various bristles.

A. dorrieni showing its lateral compression.

Head of A. dorrieni (side view)

Mouth and mouthparts of A. dorrieni (ventral view)

So, an interesting find and thanks to Dennis for passing it on to me for closer scrutiny. As ever, finds such as this are useful in determining the distribution (and in this case, spread) of species, so it is worth keeping an eye out - especially in case a third Arcitalitrus finds its way here.

References

Cowling, J.E., Spicer, J.I., Weeks, J.M. & Gaston, K.J. (2004). Current status of an amphipod invader, Arcitalitrus dorrieni (Hunt, 1925) in Britain. Journal of Natural History 38: 1665-1675. 
Konopacka, A., Grabowski, M., Bącela-Spychalska, K. & Rewicz, T. (2009). Orchestia cavimana Heller, 1865 (Amphipoda: Talitridae) enters freshwater inland habitats in the Vistula River, Poland. Aquatic Invasions 4(4): 689-691.
O'Hanlon, R.P. & Bolger, T. (1999). The importance of Arcitalitrus dorrieni (Hunt) (Crustacea: Amphipoda: Talitridae) in coniferous litter breakdown. Applied Soil Ecology 11: 29-33.
Peart, R. & Lowry, J.K. (2006). The amphipod genus Arcitalitrus (Crustacea: Amphipoda: Talitridae) of New South Wales forests, with descriptions of six new species. Records of the Australian Museum 58: 97-118.
Richardson, A.M.M. (1980). Notes on the occurrence of Talitrus dorrieni Hunt (Crustacea: Amphipoda: Talitridae) in south-west England. Journal of Natural History 14: 751-757.