Where there is light …

It’s been a couple of weeks since I last ran the trap thanks to a combination of cold weather and busy weekends so I was delighted to find two December Moths in there on the night of 2nd December.

I love these moths. The very fact that they come out when the weather is at its coldest, their ‘woolly’ appearance, the smart patterning and the fabulous antennae of the males makes for a great catch every time.

Other than that it’s been very quiet with insects – the odd Silver Y being the only other moths of interest (see photo at top) – and so I’ve been taking the opportunity to do some reading. One thing I came across via Twitter was an article which went some way to answering a question that I’ve been thinking about for some time now, namely, what fraction of the moths near my trap am I actually catching? Do moths come from miles away to the MV light, or do they need to be passing close by? And does it depend on the moth? This seems like an important question to me, not just from the point of view of wanting to catch as many species as I can, but in terms of keeping records and contributing them to the National Moth Recording Scheme.

I know already, of course, that not all moths come to light. Some species/families need pheromones to attract them, for example the elusive clearwings. I’m also aware that keeping records that are informative about populations and commonality requires other factors in place, such as constant effort, as well as expertise in identifying the more difficult ones. However, if these things are controlled it still assumes that moths come in equal proportions to any single trap. In a 2014 volume of Insect Conservation and Diversity Merckx and Slade (2014) report on a field study in which various species of moths from three families – Geometrids, Noctuids and Erebids – were captured, then marked (with a pen) and re-released to see if they could be recaptured in a nearby portable, actinic trap; a so-called Mark, Release, Recapture (MRR) test. I have quoted the full abstract below, but in essence the experiment suggests that moths from different families are attracted at quite different ranges and that even for those flying within a metre of the light the proportion becoming trapped was significantly different in each family.

In terms of the first of these, erebids (the family including Snouts, Herald, Straw Dot etc.) had a range of 27m, measured in terms of a minimum 5% recapture limit(i.e. beyond 27m the fraction of moths recaptured dipped below 5% of those released). In contrast, Noctuids had only a 10m radius for the same 5% limit for recapture.

In terms of the second, of moths flying within 1 metre of the trap 55% of erebids were recaught, but only 10% of noctuids and 15% of geometrids. It’s also worth mentioning that the experiment was conducted in two locations – woodland and open space – and that moths were released from the same radii at different angles round the trap (N, S, E, W etc.). The direction round the trap had some small wind-speed effects, but the traps in (dark) wooded areas had much better recovery rates pointing to the negative effect on recapture of extraneous light in the atmosphere (and see also here for another paper which has demonstrated the quite severe effect on breeding success of light for geometrids).

So what does all this tell me? Well, first that it’s still fun to trap moths! … but also that I may need to be more cautious about drawing conclusions about the relative density of particular species in the area. It is about 10m from the space at the back of my house to the end of the garden and hence if noctuids’ range is about this distance that will be telling me the numbers that are in, or flying over/close to my garden itself. On the other hand, if erebids and geometrids are more likely to be pulled in from distances of 25m+, I’m likely to be gathering these moths from the local surroundings, which for me include a number of mature trees and shrubs. Moreover, of the moths coming close-in to the light the noctuids may be under-represented in terms of numbers compared to other families. Nonetheless, it’s worth also being aware that the experiment was conducted with a low-wattage actinic lamp and I run a high wattage MV bulb, so it may well be different. Moreover, as Merckx and Slade note:

[C]are must be taken in relating the abundance of the sample to absolute local abundance. Frequent sampling can provide adequate data on relative temporal change in the local macro-moth fauna, however.

As we enter the end of the year I’m looking forward to reviewing my catches from 2017 and comparing them to 2016 … but with appropriate care in terms of my conclusions.

 

Reference:

Merckx, T., & Slade, E. M. (2014). Macro-moth families differ in their attraction to light: implications for light-trap monitoring programmes. Insect Conservation and Diversity, 7(5), 453-461. doi:10.1111/icad.12068

Abstract. 1. Light traps are used to make inferences about local macro-moth
communities, but very little is known about the efficiency with which they
attract moths from varying distances, and how this may differ among families.
2. We released 731 marked individuals, from three of the most common and
species-rich macro-moth families, at several distances from low-wattage actinic
light traps in open and woodland habitat.
3. Logistic regression showed family-specific sampling areas: erebids were
attracted from up to 27 m, geometrids from up to 23 m, and noctuids from up
to 10 m from the light source, with these distances corresponding to a 5%
recapture rate. Sampling size was also family-specific: a maximum of 55% of
erebids, 15% of geometrids, and 10% of noctuids were predicted to be trapped
when flying near (0–1 m) light traps.
4. Our study demonstrates that weak light traps: (i) have remarkably local
sampling ranges, resulting in samples that are highly representative of the local
habitat, and (ii) attract small, and family-specific proportions of individuals
within these ranges.
5. We suggest that the local sampling ranges of weak light traps make them
excellent tools to monitor nocturnal macro-moth communities. As trap efficiency
differs among macro-moth families, care must be taken in relating the
abundance of the sample to absolute local abundance. Frequent sampling can
provide adequate data on relative temporal change in the local macro-moth
fauna, however.

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A quick update …

After a long, frantic period at work I finally found the combination of time and dry weather to set the trap a few times. The strong winds of the last few weeks, with storm Brian bringing warm air up from Africa and Southern Europe, have disappeared and with them many of the rare moths that have been cropping up all over the Southern half of the country. Having missed all the action I was still optimistic of catching something rare … but lady luck was not on my side.

Nonetheless, there were a few immigrant moths. The best was this beautiful Vestal:

The fieldguide notes that the colour of the moth is dependent on the temperature to which the pupa was exposed, with warm straw colours such as this one associated with cooler (relatively) temperatures. Warmer pupae tend to develop as paler moths with brighter pink-ish stripes. I suspect, therefore, that this one was from somewhere in the Southern France area, rather than further south in African climes.

It might well have blown north with the second migrant, this beautiful silver Y. I just love the subtle colours of this moth …

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The remaining moths are less interesting in terms of journeys travelled but are wonderful in terms of the way they reflect the Autumnal colours that are everywhere around us. The damp weather brings out the greens and browns of tree trunks and the sparkle of water droplets and wet leaves and, with them, the moths at this time of year are similar hues and patterns.

Examples are plentiful but here I have Cypress Carpet, imitating the bark of a Cypress tree …

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… this November moth (agg.) uses a similar pattern to blend into the browns of Autumn leaves …

… Spruce Carpet, again looking for all the world like the pattern on the bark of an evergreen of some sort …

… more splendidly, the shining green and brown of this Green-brindled Crescent which fits perfectly into a damp tree canopy …

… and finally, my favourite, the wonderfully named Merveille du Jour which one would be hard pressed to see hidden in a patch of moss …

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The only other moth of note was this micro, new for the garden, which is Phyllonorycter messaniella:

With work easing off just a little in the next few days, I’m hoping to add to this tally and pull in some more of these Autumnal moths.

Insects update

We’ve had a sustained spell of quite wet and windy weather, though with sunny spells, if you can find them, punctuating the cloud in places. I’ve not even set the moth trap – though I did miss one potentially good, muggy night and was kicking myself. Even so, insects are still on the move, as are the birds with swallows making their way slowly south. I walked the dog on Orcombe Point this morning and four juveniles were hawking for prey over the top field, hanging motionless in the strong wind and then wheeling and diving with consummate skill. Meanwhile, in the estuary, the Dawlish Warren website was reporting a Grey Phalarope in the Bight, perhaps epitomising the stormy nature of the weather. Nonetheless, Matt has also found three Portland Ribbon Waves in a local site, attracted to overnight security lights, suggesting that there might be a colony nearby – see his post about them here.

Meanwhile, whilst I’ve seen nothing out of the ordinary in terms of moths, I’m still finding bees and hoverflies. This Bombus lapidarius (Red-tailed BB) was enjoying a bit of sun at the weekend in our garden.



Though it’s faded slightly in the sun, it still retains much of its red colour, the males, such as this, being more orangey than the queens and workers in the first place. Meanwhile, back on Orcombe, Common Carder Bees (Bombus pascuorum) remain active.


The lower photo shows how variable the colouring can be. Though the thorax is usually chestnut brown/orange with pale sides, from the reading I’ve done the abdomen can have varying amounts of pale, but always at least some black hairs. This separates them from the much rarer Brown-banded (B. humilis) and Moss (B. muscorum) carders both of which have only pale hairs on the abdomen. Even in windy, damp weather these bees are still active, nectaring on the few flowers remaining, the farmer having cut the hay in the main National Trust fields last week.  It felt a bit early to me, with some flowers still out, but I guess that farmers must take advantage of dry weather and, to be fair, he’d obviously been looking at the forecast!

My other find this weekend was a new species of hoverfly – new to me that is, not to science, it being a common one nationally.


This is Rhingia campestris. It’s one of two species in the genus Rhingia, both of which, uniquely, have the same, extended rostrum – the long ‘nose’ containing the proboscis, allowing it to feed on deep flowers. It’s relatively common across the whole of the British Isles and bivoltine – two brood generations – with the second coming to an end now. As with all the hoverflies it’s easily overlooked if you are not actively searching for them.

But then that’s true of so much, isn’t it? Seeing is easy; it’s noticing that’s difficult.

Autumn’s arrival …

The mothing has been pretty dire of late with very little to report other than a nice number of Vine’s Rustic.


This is a moth that I didn’t trap very much last year according to my records, but I think this was more to do with my inexperience and categorising it with the Uncertain and Rustic Agg. The ones this year stand out as silvery/grey, with larger kidney and circular spots – or perhaps my eye is just more attuned than it was.

Other than this, and the annual influx of Large Yellow Underwing at this time of year, little has demanded an ID. This has meant that I’ve been able to continue looking more carefully at bees and after my success with a new Bumblebee last week – B. jonellus (Heath BB, below) – I’ve been keen to see what else is out there …

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As August has turned into September, the number of bees on the wing has reduced considerably. It’s also noticeable that males seem more numerous than females. Queens have stopped producing female workers and have been turning their attention to males whose job is to mate with new queens as they eventually leave the nest. These males are ‘evictees’ – unlike the workers they aren’t allowed to stay in the nest and have to find places to roost when not on the move, awaiting their chance to fulfil their role in life. Once you know where to look they are readily seen, such as this sun-bleached male roosting under a clover leaf on Orcombe Point above Exmouth beach.

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The queen B. lapidarius is the biggest of our Bumblebees and this (smaller) male seemed to be snoozing happily in the sun. At the other end of the scale, today I walked the dog in a howling gale and driving rain. Only the kite surfers hammering across the estuary seemed happy to be there and even the dog was keen to jump back into the car. Nonetheless, turning over a few flowers soon revealed this little chap sheltering from the storm on the leeward side of the thistle flower.

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I’m not sure about it, but I believe it’s another one of the ‘sweat bees’, from the genus Lasioglossum, which I posted about the other day.  I think that this is L. smeathmanella, but it’s really a guess based on the white mark on the face. Comparison photos from Steven Falk’s Flickr feed can be found here.

The final bee, found yesterday before the rain came in, was this one.

This time it’s a female, one of the Leafcutter bees – Megachile – so called because they use pieces of cut leaf to build their nest cells. With the help of Twitter I think it’s Megachile centuncularis, Patchwork Leafcutter Bee. The extent of the orange pollen brushes on the base of the abdomen – all the way to the tip – and T6 with hairs on the top are both good clues, along with the abdomenal stripes. It contrasts nicely with M. willughbiella, Willughby’s Leafcutter Bee where the tip of the abdomen is dark underneath on T6. This lovely photo from Tim Worfolk’s Twitter feed (@TimWorfolk) shows it beautifully.

So much to learn – the bees are a complex and fascinating group of insects. Nonetheless, I hope the weather picks up enough to get back to some moths soon. I’m due a decent find or two … perhaps Clifden nonpareil? I wish …

More bees …

Matt has been doing an excellent job of covering Orcombe Point, as always, and as well as the birds he found a patch of thistle with a number of bees nectaring. His photos and a bit of detective work from me, not to mention the generous help of Twitter users, has led to some interesting IDs.

I began my deliberate interest in bees this Spring, choosing to focus on the Bumblebees as a relatively straightforward and visible group. Matt’s first find this week was Bombus sized, but entirely black and without the hair fuzz.


Clearly a female given the plush white pollen brushes, this turned out to be one of the Andrena – mining – bees: A. pilipes, Black Mining Bee.

This is a relatively scarce bee, sparsely spread along the south coast and fond of coastal, sandy cliffs in which it nests. A very similar species, A. nigrospina, is hard to distinguish from photos, but pilipes is bivoltine – breeding twice a year – whereas nigrospina is univoltine, with the breeding time between the two spikes of pilipes. The late date, along with the coastal location, suggests pilipes therefore … though a tweet from Steven Falk informed me that nigrospina was historically recorded in Devon.

The second bee was this one:

This is a much smaller bee – forewing length around 5-6mm. It’s one of the Halictus genus – End-banded Furrow Bees. From the bit of reading I’ve done, these are commonly known as ‘sweat bees’ because of their habit, in hotter climes, of drinking from the sweat of other animals, including humans. The yellow legs had me looking at H. Rubicundus (Orange-legged Furrow Bee) and the much rarer H. eurygnathus (Downland FB), about which I was momentarily excited because it has orange undersides to the flagella. In the end though it turned out to be the commoner H. tumulorum (Bronze FB) … proof of the rule of thumb, always assume it’s the commonest one!

Returning, myself, to the same patch of thistle a day later, I then photographed this bee:

It’s another sweat bee, but this time from the genus Lassioglossum – the Based-banded Furrow Bees. One key ‘immediate distinction’ (Falk, 2015: 181) is that Lassioglossum all have a smooth, shiny tergite 1 – the abdominal section closest to the thorax. I think this is just about visible on this photo, and certainly contrasting with the Halictus above which shows a hair-covered tergite 1:

There are a good number of different species in the genus, but my best guess, based on the colour of the legs and my previous rule of thumb, is L. calceatum – Common Furrow Bee. These come in two male forms, entirely black, or with red in tergites 2-4. The undershot shows the colour as mainly black here, but with a touch of red showing:

There’s no doubt that bees are challenging, but they are such fascinating creatures, with complex social lives. ID is made difficult by their movement and the concern about being stung of course! I was careful to say at the start of this post that the Bumblebees were relatively easy. On the same patch of thistle was this one …


The basic colour pattern – rear yellow stripes crossing thorax and abdomen with white tail – matches B. hortorum (Garden BB) but the face is short, not long,  with obvious yellow hairs and the body is fluffy with buff-yellow, not lemon-yellow. All these are features of the less common B. jonellus ( Heath BB). I’ve put it out on Twitter and will update as I get a response, but meanwhile, I’m excited at the prospect of another new Bumble.

[Edit: B. jonellus was confirmed by the Bumblebee Trust, so delighted by my new find!]

Ecosystems

It was a fantastic start to the morning. I’ve managed to somehow avoid ever seeing a Black Tern on the Exe estuary, despite them being annual and having spent a considerable amount of time looking over the water. For some reason it’s been a bogey-bird for me. So a week or more ago, when my good friend Matt found White Winged Black Tern – only Devon’s 15th record ever – I became one of the few birders to have this rarity on my life list before Black Tern! This morning however the world was restored to normality as two BTs appeared off the seafront and I could confirm my tick. But much better than that, for a good hour all three birds were feeding near each other and on occasions we had all of them together in the same scope view – a truly amazing sight and a once in a life-time opportunity for an inexperienced birder like me to compare these potential confusion species side-by-side and to see how they interact with their environment.

Matt’s notes do more justice to this comparison than I can here and I consider myself lucky, as always, to know someone so expert who can put me on to these birds. Such expertise  is built up over many years and ‘finding’ birds isn’t by chance. Partly it’s time; time spent watching, searching, being there in case. But it’s also about knowing how the world of birds works; what should be where and when; what could be here; how tides and winds and rain might bring in birds, or drive them under cover. It’s about being at home in the natural world and having a feel for things – understanding the ‘jizz’.

All this set me thinking about ‘ecosystems’. The derivative ‘eco’ permeates our culture, as a short-hand for anything ‘good and green’, but this tends to over-simplify the meaning. The word is derived from the Greek oikos meaning home/family. Literally, understanding the system by which home/family is established. This feels just right in describing birding and mothing because it’s more than just knowing about things. Fundamentally it’s about understanding how things come to be ‘at home’ in their environment, and how the environment provides a space to make this home; how species and physical environment fit together, and how we can be part of it all too.

This morning’s activity illustrated the idea perfectly. Both species are ‘marsh terns’ rather than sea terns, meaning that they are more at home feeding on lakes, still waters in estuaries and so on. Rather than diving for fish they surface feed, fluttering and twisting over the water looking for insects and other life at or near the surface. Breeding in Eastern and Southern Europe, they are migratory in the UK (bar a few occasional pairs) and so the fact that they have made their temporary home in Exmouth relies on finding enough food to keep them here for a week or two. The exact diet I can’t say, but perhaps it included these insects, this one found (with a damaged wing) on the coast path  as we scoured Orcombe Point for other migrants.

I’m keen on hoverflies, though still a complete novice, but some ID work at home revealed this is as Scaeva pyrastri (Pied Hoverfly). It’s relatively easy to ID with the key features shown below, namely …

Hairs on the eyes – visible below as a yellow/white blush on the eye surface.

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Protruding space between the eyes, with bulbous antennae:

And of course the characteristic white ‘comma’ marks on the abdomen.

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Ball and Morris (2015) state that it’s a migrant, like the terns, arriving in large numbers in some years in July and August, and occasionally breeding too. I don’t want to draw too strong, or unwarranted, connections between Black Terns and Pied Hoverflies, but in general terms these connections between species are everywhere and crucial to survival – the ‘system’ of being at home.

However, to a casual observer, or even a careful one who only looks at one animal/plant group, they may not be apparent. Earlier this week I came across an article in the Journal of Insect Conservation and Diversity (one of the perks of working in a university is access to all sorts of this weird stuff!). It reports on the manner in which ‘Livestock grazing disrupts plant–insect interactions on salt marshes’. You can see the abstract here, but in essence it describes a study of grazing densities (number of sheep per hectare) on a German saltmarsh and the effect on both plants and insects. In a nutshell it finds that increasing the density of sheep has limited effect on plant species composition – there still plenty of plants of different sorts and though grasses tend to dominate, other species readily survive the grazing impact. If you are only interested in plants then you might think all is ok … but look at the composition of moths (as the study did) which are making use of these plants and you find that increased grazing has a significant effect on decreasing moths species. It turns out that it’s not the number and variety of plants that seems to matter for moth survival, it’s the way insect-plant interactions work, and how they are disrupted by grazing animals. Unless you are a specialist grass moth, like this Chrysoteuchia culmella, say, then grazing stops you interacting with the species of plants you rely on, even though they are still there.

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It’s an ecosystem in action – a network of ways in which species can, or cannot, be ‘at home’ – and anyone interested in birds should take note since lots of reserves are based around marshland and grazed: think Exminster, Topsham, Slimbridge etc. Lots of cattle or sheep and the plants are fine … but the interactions between plants and moths (and hoverflies) are reduced … and terns feed on moths and hoverflies …

One thing I take from all this is the importance of being interested in different animals/plant groups – pan-interest, if you like – but also the difficulty of seeing ecosystems in action. It’s always easier to see ‘things’ than connections between things, and even harder to see the absence of things! I can see the terns (finally!), I can see the hoverflies and I can see the plants, but seeing a decline in interactions between them is challenging. So after a great start to the day it also ended well as I noted on Twitter that  the National Moth Recording Scheme, made up of data from amateur recorders like me, has just today had its 24 millionth macro moth entry logged. Big data sets make for good analysis and absence is always easier to see on the grand scale. I like to think my 2000+records to date are making a difference.

 

Reference:

Ball S and Morris R. (2015) Britain’s Hoverflies: A Field Guide: Princeton University Press.

Hoverfly

One of the things I’ve found since getting into moths and other insects is that my office at home tends to be littered with specimens, some alive and well awaiting identification and release, others that have perished and been collected since. One or two live moths find their way into the fridge too, a means of calming them down, but slightly alarming for the family. I try not to harm anything that I catch but I can’t claim that I haven’t had the odd accident and one such tragedy resulted in this Hoverfly becoming amenable for ID.



Fortunately, if my ID is correct, it’s Myathropa florea, one of the Eristalini family and a common species meaning that one accident won’t harm the population! I’ll take you through the ID process using the excellent guide by Ball and Morris that I’ve talked about in previous posts.

First, as you can see in the second of the photos above, the head sits proud of the thorax, as it does with most hoverfly tribes but crucially eliminating the big Syphini tribe.

Second, examining the wing veins shows two important features. The R4+5 vein shows a strong loop (the blue circle below) indicating it’s a member of the Eristalini (though one just needs to eliminate Merodon equestris, which is a bee mimic and quite different). I’ll return to the second feature in the yellow circle below.  


Eristalini is also a biggish tribe but fortunately splits into two groups – bee mimics and others. Of the latter M. florea has particular characteristics which allowed me to pick it out (I think!). First, the general colouring is of a wasp mimic, albeit not a convincing one.


More characteristically the thorax is described as being split by a yellow line with the rear portion of black making a ‘Batman’ shape.


It’s indistinct here – as Ball and Morris say it can be – and the poor photo doesn’t help, but I think one can pick it out, marked up here in the same photo.


Second, the guide notes that veins R1 and R2+3 reach the wing margin separately and this is clearly the case here – see the yellow circle in the photo of wing detail above.

I hope this gives you a sense of the ID journey. As they note in their book, hoverflies are hard to do but rewarding. I love their details – shown by the face here and the eyes which meet at the top, indicating it is a male.


A challenge for sure, but a good one.

 

Coda: thanks to Matt for holding onto this Bloxworth Snout which he trapped yesterday morning. Always great to see a new moth – my 366th species since I starting trapping on October 10th 2015.

Bloxworth Snout