Monday, 29 July 2013

Cottage Farm

I was invited to attend a walk around part of a 145 acre farm in NI, and this post shows some of the interesting species we found during that time. The farm has many differing habitat types, and the number of species we found is testament to the sensitive way in which those habitat types have been nurtured. Although much of the land is acidic, like my home patch, there are a few limestone outcrops, which helps to explain why so many of today's finds are new to my species index.

Himalayan Balsam is a rapidly-expanding and highly invasive species that is taking over vast tracts of ditch, riverbank and any other place near water. I have previously remarked that I have never seen any species which appears to attack it in any way: most specimens are pristine. But today, to my delight, I found some specimens that were clearly being mined:

Mines of Phytoliriomyza melampyga on Himalayan Balsam
The only miner known to attack it is Phytoliriomyza melampyga, and the initial narrow corridor leading to an eventual blotch matches perfectly. We generally find that any imported species will inevitably be followed by any native species that are dependant on it, and it looks like that has happened here at last. I'll need to keep an eye on my local specimens.

New to my species index.

Honeysuckle is clearly a nutritious plant: there are many miners to be found in its leaves. The mine of Aulagromyza cornigera is identified by the initial narrow corridor, widening to a consistent sized corridor, with a central row of frass.

Mine of Aulagromyza cornigera on Honeysuckle
New to my species index.

I don't have a great deal of Hazel on my patch, so it's always good to find a substantial amount to have a look at. I quickly found a few mines of  the micromoth Stigmella floslactella, which is identified by the frass-filled early corridor, with later sections having a clear border free from frass:
Mine of Stigmella floslactella on Hazel

New to my species index.

We also saw lots of the hoverfly Sericomyia silentis. I thought this crop showed the Hazel nicely:

The hoverfly Sericomyia silentis on Hazel
I saw a few females of the hoverfly Bachia elongata closely examining flower stems without landing. This is typical behaviour when they are searching for clusters of aphids, and when they find a suitable batch, they will lay eggs very close to them as a food supply for their larvae. No resting - no autofocus: this shot was on manual focus:

Female Baccha elongata examining plant stems for aphids
New to my species index.

I took this opportunistic shot of the Common Garden Spider, which can be recognised by the dotted white cross on the abdomen:

Common Garden Spider

There were a few clusters of Common Valerian: some on the road verge, and a large group on the slope down to the river.
Common Valerian - Valeriana officinalis
This is a very common and widespread plant, but I have never found it on my local patch. There doesn't appear to be a preference for lime, so I can't imagine why I don't have it.

New to my species index.

I was a bit surprised to find Teasel on the edge of a bog:

Teasel has the most wonderful structure, with spines in every imaginable place, and these little reservoirs at the base of the leaves:

Water and debris collected at the base of Teasel leaves
These little reservoirs are always full of dead insects and vegetation, and I have always wondered if the plant takes any nutrition from those. It seems the answer is a qualified 'yes':

Article Source: Carnivory in the Teasel Dipsacus fullonum — The Effect of Experimental Feeding on Growth and Seed Set
Shaw PJA, Shackleton K (2011) Carnivory in the Teasel Dipsacus fullonum — The Effect of Experimental Feeding on Growth and Seed Set.

30% increase in seed set is quite an improvement.

New to my species index.

A few moth traps had been set the previous night, and I managed to judge my arrival time just as the identifications were being completed. A few of the species are new to me:

Lesser Swallow Prominent - a Birch feeder - which is identified by the white triangle at the peak of the wing:

Lesser Swallow Prominent

Swallow Prominent - a Poplar and Willow feeder:

Swallow Prominent

And the micromoth Argyresthia goedartella:
The micromoth Argyresthia goedartella
All are new to my species index.

The Spectacle isn't new, but I thought this shot showed its 'goggles' very well:

Spectacle moth
9 new species isn't bad for around 4 hours.

Monday, 22 July 2013


It has been suggested (and rightly so) that I don't say very much about the techniques that I employ in order to get some of my shots. Yesterday I managed to get this rare shot of an Ichneumonid ovipositing into fly larvae hidden inside the Knapweed flowerhead:

Ichneumonid ovipositing

Ichneumonid close-up
These shots are very elusive, so it occurred to me that it might be useful to explain what went on before, during, and after the photography session.

Firstly, background information is required. Ichneumonids are parasitic wasps that lay their eggs into the bodies of the larvae of other insects: the most commonly targeted species are flies, moths, butterflies or sawflies. Timing is crucial: if the target larvae are too small, then the egg-laying process will be too difficult, but if the larvae develop too much they might already have pupated, or become too mobile, or even be able to defend themselves.  The timing is also often dictated by the foodplant of the target larva: if the plant isn't in the correct state then the female of the target species won't be able to lay her eggs. So we clearly have (at least) two timing dependencies. This means that the opportunity to take these photographs is severely limited - to perhaps a few days in each year. So in order to plan for this kind of photograph, we have to be aware of the potential timing of these events, and to monitor relevant food-plants at the appropriate time. I noticed that some females were investigating the Knapweed on Saturday, so I planned the photography session for the next day.

The female operates by flying from flower-head to flower-head, quickly testing each one with her antennae. If nothing is detected, she will quickly fly to a nearby flower-head and start to test again. The ovipositor is stored in a sheath that is held behind her, and if she detects a target, she will quickly unsheath the ovipositor and position herself so that she will insert it in the correct direction. This unsheathing and positioning takes less than a second. She then follows the unsheathing with a series of thrusts, each a little deeper, as she reaches the target larva. This thrusting might take two or three seconds: this is the opportunity for the shot. So we have to follow the female from flower to flower and take great care to observe when she appears to be taking a little longer than usual to inspect the flowerhead: this is a sign that she might be about to deploy. That's the clue to get close and be ready to focus. A fast-focussing lens is essential at this point, and I have my focussing system set to a single point. If you are focussing on a scatter system, the lens will have difficulty focussing on the insect and will get distracted by background leaves, stems or flowers. I use a Canon ultrasonic macro lens, which can focus in less than a second: essential for this kind of shot. A quick press of the shutter release when near the subject will prime the lens to be suitably-focussed: it is already nearly in the right position. As soon as she starts the injection, I am already in place with the camera primed and the lens in approximate focus. Then I take repeated shots, perhaps two shots in three seconds, so that I might get five or six opportunities from each injection sequence. Just occasionally, she will make more than one attempt in the same flowerhead - presumably to target further larvae: those are the best opportunities for a shot like this.

Most of the shots are bad: either out of focus or blurred due to hand movement, or obscured by stray, windblown leaves, or the female might have suddenly turned to get a better direction of injection. This photograph took 20 minutes to get, with probably 50 shots that went straight to the recycle folder when I was sorting the photographs later. Fortunately digital shots are cheap, so we can take as many as we like. Another reason for the long time is that the female might well decide that the local area has nothing left for her, and vanish over a hedge. This means that we have to wait for another female to come along. In addition, because we don't want to lose sight of the female, we can't pay too much attention to where our feet are going, so tripping is a frequent hazard, especially with Bramble runners nearby. Finally, when she's finished laying, she will quickly seek another flowerhead. Since we are down and close to the previous flower, we need to quickly refocus our attention to follow her movement. These can all add up to missed opportunities for the shot.

I think I might have achieved perhaps half a dozen good opportunities for a decent shot in those 20 minutes.

One final tip enables us to get that elusive shot: I call it plant-twisting. When the injection is taking place, the female is so focussed on the process that you can hold the plant stem and rotate it for the best angle for the shot without alarming her and scaring her off. (She actually couldn't fly away if she wanted to: she is firmly attached to the plant). That gives us the opportunity to rotate the plant, not only to achieve the best angle, but also to select the best background for the shot. It is no coincidence that the yellow flower at the rear of the shot highlights the ovipositor: I selected that background as I held and rotated the stem.

So all-in-all a very tricky process to get that elusive shot.

It's worth noting here that there are many hundreds - probably thousands - of species of Ichneumonid in the country, each with a unique or severely restricted range of target species. Many of the target species live in places that simply can't be photographed, but there are a few species that use prominent and available plants: these are the ones that present us with photographic opportunities.

To complete the story, the wasp's egg will hatch out, and the wasp larva will eat the host larva. The wasp larva will then pupate and hatch at the appropriate time next year (more synchronisation!). The requirement to fool the host's rejection mechanism ( the egg has to resist rejection when inside the target's body) explains why most parasitic wasps have such a small range of target species: it would be too difficult to trick all the rejection mechanisms. This is analogous to the restricted range of host plants for leaf-miners.

Monday, 15 July 2013

Unbelievable weather

We have just been through the warmest couple of weeks in recent years. This has brought out an incredible number of insects and has affected our wildlife in some very interesting ways.

The year was very late in getting started, with a long-term and very cold east wind that delayed spring by 4-6 weeks. As an example, queen bumblebees were seen hunting for nesting spots some 4 weeks later than usual. But by the middle of June I was seeing new queens and males, which is weeks earlier than usual. Bumblebee nests go through a fixed cycle. First, the queen can be seen gathering pollen which will be eaten by the larvae from her initial batch of eggs. These workers then emerge and can be seen foraging for pollen to take back for subsequent batches. The next stage is when the nest is mature, and new queens and males are created. These then emerge and start up new nests. Many nests this year have gone through those stages much more quickly than usual, and after a delayed start the nests are now actually ahead of the normal schedule. In the last two weeks I have seen fewer new queens and males, so it is clear that new nests have already been established. It seems as if the bumblebees were able to predict that we were going to experience a hot summer: so much so that they accelerated the production of males and new queens in order to produce two generations, rather than a single one. I checked my findings with the national database, and this phenomenon has been recorded throughout the country: it's not just local to me.

I accidentally discovered a new (to me) orchid site last week. Donegal International Airport is situated on a strip of land that extends out into the atlantic on our North West coast, and I had an opportunity to explore the sand dunes while waiting for a delayed flight. Coastal grassland behind dunes is often a good hunting ground for orchids and I quickly found Northern Marsh Orchid:

Northern Marsh Orchid
Pyramidal Orchid:

Pyramidal Orchid
And Fragrant Orchid:

Fragrant Orchid

These orchid species were present in their hundreds, with orchids as far as the eye could see, but what intrigued me particularly was the fact that the Northern Marsh Orchids were very 'pure': they all appeared to have no influence from other spotted orchids. This is in direct contrast to the specimens in my home location, where the Northern Marsh Orchids can have toothed lips or paler flowers. This led me to deduce that the more frequent Heath Spotted Orchid and Common Spotted Orchids were not in the close vicinity. Then I found the following specimen, which is clearly Northern Marsh Orchid in origin, but has three very well-developed lobes in the lower lip:

Hybrid Orchid
My first conclusion was that this was a hybrid between Northern Marsh and one of the other two orchids from the immediate vicinity, with Pyramidal being the most likely in terms of shape. Intergeneric hybrids are known (which tells me that the definition of genera in these orchids is wrong!), but the hybrid between Northern Marsh and Pyramidal orchids has not been documented (and I don't even know if it's possible).

Much discussion ensued (and is still ongoing), and one possible candidate that was suggested was Southern Marsh Orchid, which has strong similarities to the specimen shown. I checked the distribution map for Southern Marsh, and it is clearly a south-eastern species, and hasn't (yet!) been recorded from Ireland:

Distribution of Southern Marsh Orchid
I hunted around a bit more, and discovered that there is another orchid that I have never seen - Western Marsh Orchid. This has 3 lobes, red-purple flowers and has the correct (mainly western) distribution:

Distribution of Western Marsh Orchid
Western Marsh Orchid is known to hybridise with Northern Marsh Orchid, and the literature says that the hybrid has been discovered in Anglesey and Scotland, and 'probably exists in Ireland'. Once the various authorities have delivered their verdict, I'll update this page.

Late note: The specimen has now been identified as Dactylorhiza hebridensis, otherwise known as Dactylorhiza fuchsii subsp. hebridensis, the Hebridean Spotted Orchid.

As an aside, here's the distribution of another orchid that I have never knowingly seen:

Distribution of Narrow-leaved Marsh Orchid - Dactylorhiza traunsteineri
Compare that with the other distributions shown above, and it will be seen that this has no clear rationale behind the distribution: it goes from north to south and east to west. I cannot see anything that would govern distribution other than a bias towards coastal habitat. It seems to have a specific requirement which is scarcely found, but can be found anywhere. When I see a distribution map that looks like that I just know something is wrong. Maybe someone can enlighten me.

Coastal grassland is also home to some of the day-flying moths, with the Burnet family being very prominent. This is the 6-Spot Burnet from the same location:

6-spot Burnet Moth
The larvae and pupal cases from these can be found in vast numbers on the grasses near the coast. (The flower is Lady's Bedstraw, another coastal plant in this area)