Wednesday, 10 September 2014

Large Yellow Underwing - Noctua pronuba

One of the most common visitors to the light trap I have put out in the garden over the past month has been the Large Yellow Under-wing. One morning I counted 25 hiding among the egg boxes, all clinging on determedly, and difficult to displace. 



According to the UK Butterfly Conservation in the report "The State of Britains Larger Moths 2013" the incidence of N. pronuba has increased by 186% during the period of 1968-2007 (1). The distribution map from the NBN gateway shows how widely distributed it is.



This is a fairly large moth with a wing span up to 60mm. At rest it's not the most spectacular of moths, with a base colour of brown, and few distinguishing markings besides the kidney spots on its wings. However when it flies there's a flash of colour as the forewings spread out and expose the bright orange/yellow colours of the rear wings. As soon as it comes to rest the rear wings are folded away and hidden once more. They rest during the day, but will flash their bright hindwings if disturbed. This display may be designed to surprise and scare-off predators by the sudden flash of colour.


Moth migration has thrown up a number of interesting questions relating to the navigation challenges that they face during different climactic conditions. It has long been proposed that moths navigate according to the position of he moon. However, what about periods when there is cloud cover and the moon is not visible, a situation not uncommon in the UK. Research has shown that moths are able to use the earths magnetic field as a navigation guide. 
In one of the studies moths were placed into a cage on an overcast night, and reversed the earth's magnetic field (3). When this happened the moths realigned themselves according to the new position of the magnetic field.  How insects and animals are able to determine magnetic variations amazes me - mainly because I just don't know how it's done.

Another study by Chapman et al (4) showed that moths are able to select favourable high-altitude winds to help them travel the often long distances involved in moth migrations. The study used entomological radar (no idea what this is!)  tans found that moths were able to increase the distance travelled by up to 40%. Not a bad trick some a small thing that livess for less than a year.


The larval stage of the Large Yellow Underwing Moth is one of the pests known as a cutworm. E.A. Bowles mentioned their destructive habits in My Garden in Spring, the first in his trilogy of books about his garden in Middlesex. He suggested hunting for them by lamplight to keep them from damaging "the tender, juicy buds" of his beloved early-flowering Irises. Accidental introduction of N. pronuba into the US may constitute a major pest threat to commercial crops (5). The larvae develop between September and April above ground feeding on the stems and leaves of grasses and other plants, sometimes grazing them off at ground level. When disturbed the caterpillar adopts a 'c'-shape and this one was about 35mm in length, but they can be up to 50mm long.




References:
1: Fox, R. et al. (2013) The State of Britain's Larger Moths 2013. Butterfly Conservation. http://butterfly-conservation.org/files/1.state-of-britains-larger-moths-2013-report.pdf
2: NBN gateway. https://data.nbn.org.uk/Taxa/NBNSYS0000006193/Grid_Map. Accessed 2014-09-10.
3: Baker, R.R. And Maher, J. G. (1982). Magnetic compass sense in the large yellow underwing moth, Noctua pronuba. Animal Behaviour. 30(2): 543-8. 
4: Chapman,J.W. Et al (2010) flight orientation behaviours promote optimal migration trajectories in high-flying insects. Science. 327(5966): 682-5
5: Bechinski,E.J., Smith,L.J. And Merickel,F.W. (2009) Large Yellow Underwing: A new cutworm in Idaho. university of Idaho. http://www.cals.uidaho.edu/edcomm/pdf/CIS/CIS1172.pdf.



Sunday, 7 September 2014

Caddisfly - Halesus radiatus

Before owning a moth light trap I had not really considered caddis flies as being a frequent visitor to the garden. But over the last few months I found a number skulking among the egg boxes as I empty the light trap in the mornings. Now I struggle enough trying to identify the moths that I catch and release, but caddis flies are even more of a challenge, as they do not seem to attract the attention of the publishing world resulting in a dearth of accessible field guides. There are over 6000 species that have been described worldwide. Of which 199 have been recorded in Britain, but only 3 in Ireland (1). I think that this chap who I found in the light trap a couple of weekends ago is Halesus radiatus, but I'm open to corrections.


Caddis Flies are superficially like a moth, and are a distant relative in the evolutionary sense,  but instead of scales on the wings, Caddisflies have a fine coating of hairs. It is this coating of hairs that gives this group of invertebrates it's name Trichoptera, meaning hairy wings. I think I've said this in another post, but as I get older I forget these things, and it's always worth repeating yourself - unless your wife or daughter are in earshot. It seems that caddisfies dont develop a wide range of colours unless it's brown! 



The larval stage provides the English name of Caddisfly. This is thought to derive from Elizabeth street hawkers called caddis men. The Middle English word caddice, means a woollen braid, ribbon, or tape. Caddice men used to displays these wares by pinning them on their coats. The aquatic larvae makes protective cases from materials picked up in the habitat, including  leaves, tiny sticks, sand and gravel. But not all caddisfly larvae makes cases, but all have the ability to make silk threads. I've not looked for any caddisfly larvae, but there may be some in the small pond we have, and it may be an idea to have a look. There is an interesting and accessible description of the life cycle of the caddis fly on the Fresh Water and Recorders Scheme website (2).


1: Nature Spot. http://www.naturespot.org.uk/taxonomy/term/19486. (Accessed 2014-09-08).
2: Fresh Water San Recorders Scheme. http://rasp.freshwaterlife.org/recorders/publications_resources/how_to/caddis/life-cycle.html. (Accessed 2014-09-08)

Wednesday, 3 September 2014

Rosy Rustic Moth - Hydraecia micacea

I was able to put the moth trap out again on Sunday evening, hampered previously by the awful weather and being away. Sunday evening was mild and dry, but there was a very light drizzle on Monday morning. So I wasn't setting much hope for a large or varied haul. But as. I started taking out the egg boxes I kept on turning up 21 Large Yellow Underwings, 4 Lesser Yeollow Underwings, a single Double Striped Pug (Gymnoscelis rufifasciata, a Setaceous Hebrew Charcter (Xestia c-nigrum), and a rather non-descript, well at least to me, Rosy Rustic (Hydraecia micacea). More about the others another time, but I have to admit to being intrigued by the name of the Rosy Rustic.


As you can see it's not the most colourful of moths with a uniform brown base colour. Even the kidney marks on there wings don't stand out very much. This fairly bland marking and colouration meant it took me a while to identify it.

It has a single generation and flies from August through to October. The eggs don't hatch but over winter as an egg. The larva start appearing from April to early August. Feeds at first in the stem of the foodplant and then later on the roots. When the larva is ready it pupates underground without a cocoon (1). It's a UK resident and the distribution map from the NBN Gateway shows that it can be found throughout the British Isles (2).



Despite being a rather bland looking moth it has been identified as a potential economic pest for some crops (3,4). That said there isn't a great deal on the internet about it. But my garden is safe, no potatos and no hops, except for the ones that are already bottled.



1: Waring, P. And Townsend, M. (2011) Field Guide to the Moths of Great Britain and Ireland. British Wildlife Publishing.
2: NBN Gateway. https://data.nbn.org.uk/Taxa/NBNSYS0000006466/Grid_Map. Retrieved 2014-09-03.
3: French et al (1973) Biology, Damage and Control of Rosy Rustic Moth, Hydraecia micacea (Esp.), on Hop. Plant Pathology. 22(2): 58-64.

4: Rings, R.W. And Letzler, E.W. (1982) Two newly detected noctuids (Hydraecia immanis and Hydraecia micacea) of potential economic importance in Ohio. Ohio J. Of Science. 82(5): 299-302.