The wondrous diversity of garden bees

About a month ago, I posted some musings about what can be found in a bee-friendly garden - after all, problems with a decline in pollinators are well documented and gardens can be an essential habitat. So, after a few weeks of largely warm dry weather (not typical for April in England!), I thought I'd see what was using our little suburban strip of goodness...

The Hairy-footed Flower Bee (Anthophora plumipes) remains active (particularly females) and are now visiting the wider range of plants that are available - lavender is very popular. However, these have probably been outdone on the activity stakes by the Tawny Mining Bee Osmia rufa. These have spent the last week or two mining soil from the damper parts of the garden (there's a flurry of activity when the garden has been watered) and taking it to the bee log where the drilled holes have been well used. These contain cells formed in sequence with the entrance sealed with packed soil. I shall await the appearance of the early summer generation soon; the log will be stored in the shed to over-winter from late September until being hung up again in the spring to await emergence of the next generation. Not only that, but they are great pollinators, especially of fruit trees, and our garden has apple, peach, quince and cherry either in or adjacent to it.

Female Osmia rufa basking on a paving slab - note the short prongs on the face just below the antennal bases; these are used to tamp mud into place.

 

Mmmm... soil

Back to the log

Spot the completed holes - and the retreating bee-bottom just right of centre

Of course, there are plenty of other bee species which could use a suburban garden, and several of these (some of which I have yet to identify as I'd need to capture them) have indeed appeared. Some are commonly seen like the the Buff-tailed Bumblebee Bombus terrestris and of course the essential Honey Bee Apis mellifera; others may be less familar e.g. leaf-cutters of the genus Megachile, and other genera such as Andrena and Lasioglossum. Some very general observations suggest that many of these are nesting elsewhere but using our garden a source of food i.e. I have seen several species which appear to always fly in, feed, then fly out again.

Another bee-bottom, this time approaching a clematis flower

A specimen of Bombus terrestris found deceased - note the sting rarely deployed in life

A small bee, possibly of the genus Lasioglossum

Bee caught in flight; probably Andrena haemorrhoa

Most of this activity is, at least on the surface, pretty harmonious (feed, collect, breed), but nature being nature, that's not the whole story - where there are breeding adults, there are eggs and larvae, and hence parasites. For example, Fabricius' Nomad Bee Nomada fabriciana parasitises Andrena bicolor and I have found both in the garden, the latter on dandelions. Similarly, the nests of Osmia rufa are parasitised by the jewel wasp Chrysis ignita, which I have again recorded in the garden, although I haven't yet found a specimen that would stay still long enough for a clear photo. I'll also be on the lookout for more host-parasite pairings, so do watch this space for updates.

Nomada fabriciana - note the red and black antennae (and the unwanted household fluff)

To finish, a couple of days ago I found another specimen dead on the window-sill - this has just been ID'd as the common small bee Lasioglossum calceatum - enjoy the images...

Dorsal view of L. calceatum

Wing veins - on the forewing, vein 2m-cu is weakly S-shaped and does not bulge outwards at the rear end. Hence this is not a species of Colletes. Also, the cross-veins become thinner towards the wing-tip and the basal vein is strongly curved.

Abdominal tip (5th tergite) with the small teardrop-shaped area surrounded by dense hairs. Pale flattened hairs at the side of the segmental bases.

A bit out of focus, but clearly with pollen-collecting structures (scopa)

Diary of a farm pond: April 2011

As you may know from one or two other posts, and the 'Wildlife of Highbridge Farm' page over on the right, about a year ago I got involved with a community farm project at Highbridge Farm, Hampshire, southern England. Although its main function is to grow cheap, chemical-free food without reliance on oil/petroleum products (it's a project of the local transition group, ETNet ), this comes with an interest in, and reponsibility for, wildlife and the wider environment. So, formed from an old farm gravel pit, a pond has been created and I intend to follow its development as a wildlife habitat.

The pond/gravel pit, summer 2010

Early on in the project, the pond was essentially a gravel pit which had partly filled with water and become colonised by ruderal marginal plants plus dense floating algae. Obviously this has some wildlife benefit and a few common species of Odonata (dragonflies and damselflies) were seen using it, but the idea was to enhance its ecological value. The green tarpaulin covers a small water pump as the pond is used for irrigation when necessary - something that will continue as the habitat develops.

The pond, April 2011

Over the 2010/2011 winter, many of the ruderals were removed, along with the blanket of algae. The second photo shows that the sides have also been reprofiled, and on the right is an area which has been sown with native wild flower seeds suitable for a stony substrate - behind these (off-photo) are rows of native fruit and nut trees. Some of the ruderals remain or will be allowed to return - after all, nettles (Urtica) and docks (Rumex) are important for many invertebrates - but this work should provide greater biodiversity. However, there's only way to really see how effective such conservation work is, and that is to monitor what lives there. Sounds like an excuse to rootle about for invertebrates...

Although mid-April is a little early for Odonata, on 16th April there were two exuviae (skins) of nymphs that has crawled up marginal plants and emerged as adults.

An exuvium - but which species?

The relatively small size (approx 15mm long plus another 5mm or so for the caudal lamellae at the end of the abdomen which have stuck together) and narrow form make this a damselfly rather than a dragonfly, and so I headed for the excellent little book by Cham (2009). Given the early time of year, there aren't many possible species and I was guided by which I had seen last year. So, I soon came to the Large Red Damselfly (Pyrrhosoma nymphula). This species is relatively stout for a damselfly nymph/exuvium and matches the photo very closely - it has relatively long wing sheaths and a short abdomen, and the back of the head has a rectangular shape (ignoring the central dent).Before emergence the femora would have faint dark band and the lamellae would usually have pale markings but these have now disappeared. I haven't seen this year's adults yet, but at least I know they are probably around somewhere.

A variety of other invertebrates are present at the pond - whirligig beetles (Gyrinus sp.), pond-skaters (Gerris sp.), honey bees, some as-yet unidentified diving beetles, springtails (Collembola) and wolf-spiders (Lycosidae, especially Pardosa sp.) on marginal stones, and water snails; however it is the flies (Diptera) that currently appear to be most diverse (or at least most obvious).

The first recorded this year was a pair of craneflies Tipula vernalis, a spring species mating on a small remaining patch of floating algae in late March. Soon after in April, the bee-fly Bombylius major was noted, along with others including the non-biting midge Chironomus anthracinus, the hoverfly Rhingia campestris and the moth-fly Boreoclytocerus ocellaris though it's worth noting that some of these need collection and closer examination to identify them with certainty. Moth-flies are certainly under-recorded and it's worth getting a copy of Withers (1989) if you are interested; it's currently available for just £4.

Tipula vernalis, busy making more craneflies

Male (plumed antennae) Chironomus anthracinus

The moth-fly Boreoclytocerus ocellaris

The hoverfly Rhingia campestris showing the long rostrum

There's already more (with a few more pics below), but I think initial indications are good - a wide range of colonists already this year to supplement the species persisting from before conservation works on the pond. It is unclear what impact the current dry spring weather is having, though the pond is likely to have some hydrological connection with the nearby River Itchen so hopefully water levels won't get too low. Anyhow, further updates will follow - until then, enjoy the following:

A honey-bee Apis mellifera; a very orange form, maybe the Italian strain?

Tadpoles of common frog Rana temporaria, plus a water snail

References

Cham, S. (2009). Field Guide to the Larvae and Exuviae of British Dragonflies. Volume 2: Damselflies (Zygoptera). British Dragonfly Society, Peterborough.

Withers, P. (1989). Moth Flies. Diptera: Psychodidae. Dipterists Digest 4: 1-83.

Bird pellets - they're not all about owls

Any book about the signs of wildlife will mention owl pellets - there's even an excellent little book about analysing just these (Yalden 2009), plus a fold-out laminated guide (Thomas & Shields 2008). However, many other carnivorous and omnivorous birds also produce pellets and so regurgitate indigestible material - raptors, gulls, corvids; if I remember rightly, Chris Packham even showed a kingfisher pellet on Springwatch (or was it Autumnwatch?). So, when I recently found a Tawny Owl (Strix aluco) pellet the same day as a Blackbird (Turdus merula) pellet, what could I do but dissect and compare them...

With owl pellets so well documented, I started with this one - approximately 55mm long and 30mm wide in the middle and consisting of greyish fur with some emergent bones. The habitat (under a couple of tall trees in a suburban location where I have heard tawny owls) plus the overall size, form and structure/content, lead me to ID it as a tawny owl pellet.

The owl pellet

The method is straightforward enough (if a little time-consuming and fiddly) - put the pellet in a white tray and dissect with mounted needles and fine tweezers. Pellets can be wetted, but I decided to leave it dry (either is fine). I started with the larger bones and found that, unsurprisingly, the owl had been eating voles - Field Vole (Microtus agrestis) and Bank Vole (Myodes glareolus).

Field vole lower jaw - note the toothless curved area (diastema) on the right

Field vole lower jaw - note the alternating loops of the teeth

Bank vole lower jaw - note the opposite loops of the teeth

A long bone of a small mammal, presumably one of the voles. The tiny yellowish spike near the upper left side of the bone is the chaeta (bristle) of an earthworm.

A tiny bone - assumed to be a vole 'toe' bone

Working through the pellet, another feature soon became obvious - the presence of a large amount of sand. This is a good indication that the owl had been feeding on earthworms and so ingesting sandy soil - something confirmed by the numerous chaetae present (there's one in the 'long bone' photo above). Overall, nothing too surprising - field voles are a favoured prey of many owls (though less so for tawny owls), and earthworms are comminly found. If I were undertaking a detailed study of owl diet or local mammal availability, I could weigh the different components to derive more information - in this case it's just a one-off pellet.

Now, onto the blackbird pellet. Firstly how do I know it's a blackbird pellet? Well, there the size (about 20mm long) and clear presence of invertebrate food (see below), but it was also found in my garden under one of the bird's favourite perches, and to make it even easier, I saw it deposit the pellet! So, what was in it?

Blackbird pellet

Well, the first thing that leaps out is the presence of complete millipedes - two were present and were clearly not easy to digest. I have yet to identify them, but they appear to be the same species - maybe Tachypodoiulus or Cylindroiulus - I'll need to check the telson (last 'tail' segment) to be sure. However, this is only about half the pellet - there are lots of smaller fragments, including a small green object bottom left...

A fragment of insect cuticle

The same fragment from the inside

This piece of cuticle is hard to ID, but my feeling is that it may be part of a shieldbug, though I can't be certain and I don't know of the depth of colour might change during its time inside the bird. There were many many other arthropod fragments - pieces of cuticle, antennae (at least some from small beetles, possibly Carabidae, ground beetles), bits of plant material, and various mystery structures. As with the tawny owl, there were also earthworm chaetae - given how often blackbirds are seen pulling at worms, this is unsurprising!

These are only single examples of pellets (do blackbird pellets often contain a large proportion of millipede remains?), so I can draw few conclusions beyond simply being interested in what could be found. However, I have kept the resulting bits (my wife is so proud...) and will look out for more to see if more data can be gathered. I've also found a nearby otter (Lutra lutra) latrine with numerous spraints, and have a copy of Conroy et al. (2005), so don't be too surprised if a future post invoves close-ups of the contents of otter poo...

References

Conroy, J.W.H., Watt, J., Webb, J.B. & Jones, A. (2005). A Guide to the Identification of Prey remains in Otter Spraint (3rd ed.). The Mammal Society, Southampton.
Thomas, L. & Shields, C. (2008). Guide to British Owls and Owl Pellets. FSC, Preston Montford.

Yalden, D.W. (2009). The Analysis of Owl Pellets (4th ed.). The Mammal Society, Southampton.

What's in a gall? Parasites and photobionts...

Something that has begun to fascinate me over the last couple of years is cecidology - the study of galls. I am by no means an expert in this, though I have been drawn to joining the British Plant Gall Society (BPGS) and last year even led a gall-hunting trip (another one's booked in for later this year). Why? Well, good question - it's a combination of factors - the diversity of forms, the fact that finding and IDing galls is often easier than finding and IDing the tiny invertebrates that create them (of course, some are made by bacteria and fungi), and the lack of knowledge about them - exactly how galls form, the ecology of many species and so on. So, when rootling around under an oak (Quercus robur) a couple of days ago, I found a couple of old brown Knopper galls of the cynipid Andricus quercuscalicis and decided to bring them home for a closer look...

The familiar knobbly form of a Knopper gall (green when fresh, woody when older)

The Knopper grows as a gall on acorns forming a series of protrusions as seen above with an exit hole at the top. Cutting it open however starts to reveal a tiny world of finer structure.

One bisected Knopper...

This shows a thick woody outer wall with an approximately conical chamber inside with thin vertical partial walls or flanges, and the exit hole at the top. Now, looking closer still...

Zooming in on the chamber and one of the protrusions.

Above you can see some other structures - a green-grey mass near the centre and a couple of small yellowish ovals near it (more on these below). Top right is one of the projections and the section shows a pitted texture with a smooth line running through it. I have no idea what this line is - does it provide strength like a laminate or reinforcing bar? Zooming in again shows the pitted structure to be closely packed cylindrical cells.

Cells within the wall of the Knopper gall

Egg case or larval skin?

Even this view has a linear structure running through it - so far I've been unable to find out more, or perceive any deeper structure, but I will keep looking, and welcome any comments on this. Now, the tiny yellowish structures - I think they are either egg cases or shed larval skins (exuviae), but I could see much structure even under higher magnification so have left that for the moment, and a couple of darker structures are what I believe to be frass (insect faeces). The green-grey tufts are a little more interesting though.

Close up of tufts inside the gall

A few possibilities sprung to mind - a lichen, or a microfungus - maybe some sort of mould growing on invertebrate detritus. A quick bit of work with a hooked pin and a microscope slide and the following appeared from the same material:

Filamentous green or blue-green alga

Numerous fungal spores and tiny hairlike structures

From these pictures and the general look of the tufts, I was initially pretty sure this was a lichen - a symbiotic arrangement of fungus (metabolising dead organic matter) and the 'photobiont', a photosynthesising alga or cyanobacterium associated with in. I was thinking of trying to ID the 'photobiont', but a handy comment (see below) suggests that it is a mould along with a separate alga after all (the title stays though!). I've developed quite a few questions from this one common gall, but that's one that may have been answered. Anyhow, that would have been as far as I could get for now, until I noticed a tiny flicker of movement and found this...

A tiny metallic green wasp

And closer in...

Yes, it is a tiny (2mm tops) chalcid - but not the gall-causer which is a more rotund shape and brownish in colour. This is one of its larval parasites and belongs to the family Pteromalidae. It looks very similar to some other families such as Ormyridae and Torymidae but is distinguished by the narrow pronotal collar, long stigmal vein on the wing and some features of its sculpturing. The genus is uncertain (it really needs a well prepared specimen under high magnification), but is likely to be Cecidostiba sp. Once I've been shopping for the 'Oak Galls of Britain' book (from BPGS's publications page), I may know more.

So, that's where I've got to so far - some interesting observations (I think so, anyway) and plenty of unanswered questions, so as ever, comments and suggestions are welcome. I suspect I'll learn a lot in about a month when the New Naturalist 'Plant Galls' book comes out (already on order...) and will post updates if any of my questions are answered. Until then, enjoy the following gratuitous pteromalid close-ups - a truly lovely little parasite!

Head showing crooked antennae, red-brown eyes with ommatidia (facets) and red-brown ocelli.

Dorsal sculpturing

Iridescent wings and venation

A ventral view, also showing the long stigmal vein

A slightly broader dorsal view.

Ecologist + shed = home-made canopy sampler

Today, it's time to move away from obscure invertebrates and have a look at the kit I use to find some of these things - not the usual pooters, beating trays and nets, but something a little more unusual.

I do quite a lot of invertebrate-hunting in all sorts of habitats - grasslands, heathlands, woodlands, coastal areas and so on. Of these, one is particularly tricky - woodland. At ground level it's fine, but I can't help but wonder what's up in the canopy that I can't get at - certainly there's a lot of recent research into canopy ecology around the world (e.g. here) following realisation of its importance alongside some technical advances aiding the research work itself. On a large scale and/or with lots of funding, there are various options - smoking whole trees, building canopy walkways, laying flexible platforms across the treetops, and so on. On a smaller and cheaper scale, there is the option of hoisting flight interception traps into treetops and leaving them to see what falls in before returning to collect the catch. This is something I can do, but a lot of my surveys involve a limited number of visits quite widely separated. This means that traps would have to be left for too long and might suffer from interference from members of the public (unless tied off further up the trees, but that means climbing). So, I got to thinking about how to sample the canopy whilst actually on site and without having to get roped and harnessed.

This meant being able to get a sampling device in and out of the canopy at will, and that the device had to be sufficiently portable to carry by hand from the nearest access point (which can be some distance away). Although tempted by something involving a remote-control helicopter, this seemed fraught with dangers of both cost and getting it stuck up a tree. Nope, that idea was quickly scrapped in favour of something else - a lightweight telescopic pole with a canopy sampler on the end. So, how does that work..?

First, get a series of aluminium poles and cut/fit them as follows:

A set of aluminium poles, three of which have a short section of narrower pole riveted into one end so that they are interlocking. Drill holes through so that they can be fitted together and held in place with wing-nuts. The fourth one has a hook at the end to catch and shake branches and can also be bolted into place. If you think your drilling may vary a bit between poles, which would mean they have to fit in a particular order, number your first three poles 1-3...

Short section riveted into large section

Wing-nut fixing in situ

Hooked end on pole four. A wire hangs from the bend with one or more loops (to adjust the height of the sampler) at the end. This could equally be strong cord or any other suitable material.

That's the pole arrangement, but what about the sampler? This requires an inverted truncated cone open at both ends with a smooth inner surface (try an unwanted lampshade). This has a long thin bag (fine mesh; the one below was made from net curtain) sewn onto the smaller hole and strings for suspension (via a carabiner or similar clip) attached over the larger hole.

Sampler consisting of bag, cone, strings and carabiner modelled by our washing line...

This is clipped onto looped wire and the whole thing hoisted up into a tree canopy - the hook is then used to shake branches, dislodging invertebrates which then helpfully fall into the cone and slide into the mesh bag.

The sampler in action, modestly extended, and modelled lovingly by me in our back garden...

So, onto the main question - does it work? Well, I have tried it on a number of surveys and the answer is yes. The whole arrangement is 4+ metres long so with the user's height/reach means that it can sample up to about 6 metres above the ground. Although some specimens undoubtedly escape as with nets and beating trays, each use has provided species which had been missed by sampling directly below at ground level. I have yet to undertake a rigorous study but hope to find some time to quantify exactly which groups it is best for, although initial indications are that weevils are one group readily captured. I'm also hoping to find that some under-recorded canopy-dwelling groups and species are readily caught, but only time (and sampling/identification effort) will tell, so watch this space!