Friday, July 20, 2012

The Shining: Part Two

Having been blown away by the rear-end wiggle-walk antics of glow-worm larvae in May (see videos in my previous blog), we were jolly keen to return to Elham Park Wood to find some glowing adults.

So in late June, on a cool but dry evening, and after a thoroughly agreeable picnic tea amid fragrant orchid profusion at Park Gate Down, we retraced our steps in the woods. As evening fell and as our eyes grew accustomed to the lack of light, we saw wonderful things; little blips of light started appearing, like magic, in the grass next to the path. The glow-worms were glowing :-)))

I didn't want to use flash or a torch so here's the best close-up I could get.


This is a female glow-worm (OK you can only see her rear end) advertising for a mate. You'll recall that glow-worms spend about 2 years as carnivorous larvae, then in their final summer, they become adults for a few short weeks (during June/July). They don't feed as adults, they just mate, hopefully reproduce, then die. Adult glow-worms are sexually dimorphic with the females being flightless and rather similar in appearance to the larvae. The males fly and find their mates using phototaxis (movement in response to light) (Booth, Stewart & Osorio 2004). Here's a rather good photo of a male from Wikipedia.

Male glow-worm by Hectonichus, 2007, taken in Italy and used here under a 
Creative Commons Attribution-Share Alike 3.0 Unported license.

It's a magical experience lying on a cold, damp gravel path in the middle of a dark forest gazing at a little insect wiggling its bioluminescent bottom. I can't recommend it enough.


Time for a joke?
A glow-worm walks (make that 'wiggles') into a bar.
Bar-tender says 'What can I get you mate?'
'I'll have a light ale please.'

Enough of this light-hearted humour. Back to ecology. So, how does a glow-worm glow? Glow-worms are bioluminescent; able to produce and emit light via a internal biochemical reaction (literally it means living light). I was going to summarise the biochemical processes involved but Dr John Day does an excellent job of that here. It's all catalysed by the marvellously useful enzyme luciferase, which is named after Lucifer, the 'light bringer'.

Once the females have mated successfully their glow diminishes. Their job done, they die soon after laying eggs. Larvae do apparently emit a low glow, which we looked for in May but didn't see.


These ladies do not just light up their behinds and sit there. On no. These girls know how to move. They wiggle their rear-ends alluringly. You can just about make out some of their 'come and mate with me' grooves in my poor quality video.

video

As with so much wildlife on our crowded isle, glow-worms have decreased in numbers over the past decades. They are rarely found on 'improved' agricultural land, preferring less disturbed grassland. They are most 'common' in the south on chalk grassland (Gardiner, 2009). As glow-worms are unable to move to colonise new areas (the females are flightless) their numbers have declined as habitats become fragmented and, in some cases neglected (Gardiner, 2009).

Development and light pollution are ongoing threats to glow-worms. A recent study from the University of Southampton is concerning, finding that low levels of light pollution (lower than previously thought) can reduce the effectiveness of glow-worm reproductive signals. Males were unable to locate females in even dim artificial light, because the female's signal is drowned out (Bird & Parker, 2011). No wonder we've only found glow-worms on dark woodland rides......

Like Sir David (quoted this week in an article in the Indie) I'm generally rather pessimistic about the future for our wildlife and natural habitats. So many pressures on land from so many people. And a government uninterested in sustainability (see George Monbiot here for an acerbic take on Rio+20 and the evolution of 'sustainability' to 'sustainable development' to 'sustainable growth', an entirely different concept to the original). 

How many people have seen a glow-worm glow? Perhaps Sir Winston Churchill did. Here's a quote attributed to the great statesman; 'We are all worms, but I do believe I am a glow-worm' (see Bonham-Carter, 1965).

Further Information and References

Bird, S & Parker J (2011) Low levels of light pollution may block male glow-worm’s (Lampyris noctiluca L.) ability to locate females. Journal of Insect Conservation. Abstract only here.

Bonham-Carter, Violet (1965) As I knew him. London: Eyre & Spottiswoode and Collins

Booth, D Stewart, AJA & Osorio, D (2004) Colour vision in the glow-worm Lampyris noctiluca (L.) (Coleoptera: Lampyridae): evidence for a green-blue chromatic mechanism. Journal of Experimental Biology. Volume 207, pages 2373-78. Abstract here and editorial here.

Gardiner, T. (2009) Glowing, glowing, gone? British Naturalists’ Association, Corby. Full pdf here.

An early account of glow-worm natural history is by George Newport (1856) On the Natural History of the Glow-worm (Lampyris noctiluca). Journal of the Proceedings of the Linnean Society (Zoology). Volume 1, Issue 2, pages 49–71. Available online here. An even earlier account from a 1793 volume of The Gentleman's Magazine is here.

This looks like a super new book which I'd like to read when it's published in 2013; Dr. John C Day 'Fireflies & Glow-worms'.

BUT....if you want to know more about glow-worms go no further than Robin Scagell's excellent site. If you see a glow-worm you can send him your record via this website: http://www.glowworms.org.uk/

Thursday, July 19, 2012

The Shining: Part One

Despite the worst depredations of the British weather this summer* I've seen some wonderful wildlife so far in 2012. We had some gloriously sunny days earlier in the year and woodland walks are a delight on a crisp winter's day. One such delight was a visit (on February 25th) to a Woodland Trust managed site, Park Wood near Chilham.


Park Wood is remnant ancient woodland and part of the larger Forestry Commission managed King's Wood complex. [Here seems a good place to note our government's recent, most welcome announcement that they won't be selling off publicly owned woods after all. What a shame it took public outrage, petitions and independent advisers to apprise them of the obvious foolishness of their original plan. Sigh.]

You never know what you might find if you peek underneath a fallen log and beneath one I found a real treat; a hibernating glow-worm larva. [You can tell it's a larva and not an adult because it has pale tips at the end of each segment - and the time of year is a giveaway.]


This little beastie was less than an inch long and unsurprisingly very lethargic. A few quick pictures and we put it back in the dark, damp leaf-litter under the log.

Glow-worms Lampyris noctiluca are our only resident firefly (although they are neither worms nor flies; they are beetles). Lampyris is from the Greek meaning 'shining one'. Noctiluca is derived from Latin meaning moonshine or night light. Although best known for the bioluminescent activity of the adult females, they actually spend most of their lives as larvae - about 2 years. The adults don't feed and only live for 2 weeks or so using stored energy reserves - they mate and die. The larvae on the other hand are voracious nocturnal carnivores hunting slugs and snails, which they first inject with a paralysing digestive fluid before devouring their prey using their specialised mouthparts. They hibernate under logs or in leaf litter. [Information on glow-worm ecology is from the UK Glow-worm Survey website.]

We reported the find to the Woodland Trust and Robin Scagell at the UK Glow-worm Survey. It appeared to be the first reported record for this site. Happiness :-) An unexpected encounter indeed. We planned to go back in the summer.......

As it happened the weather* has been a bit off so the return to Park Wood is yet to happen.

However, in late May, having just visited Park Gate Down for an orchid fix, we stopped for a late evening stroll through the Forestry Commission managed Elham Park Wood (part of Lyminge Forest.)


In the gloaming and within about 20 yards of the barrier we nearly trod on some small wriggling things making their way across the gravel forestry track.....on closer inspection....


......Yay!!! More glow-worm larvae :-) And far from lethargic this time.


This is another larva because of those pale tips to the segments. Glow-worms exhibit sexual dimorphism; males and females are markedly different. Females actually resemble the larvae and are flightless. A (small) picture showing the difference between the adult female and a larva is here. Males have wings and look like this.

The larvae have a curious and distinctive locomotion, not unlike that of Geometrid caterpillars (inchworms); using their rear ends for traction.

video

They moved surprisingly fast.

video

We continued on our way with great care and counted 20 individuals, all larvae, wriggling across the track in a 30 minute walk. Absolutely superb insects.


We'd never seen anything like this before. A revisit to Elham Park was agreed to be a MUST.



* Footnote: I hesitate to blame the weather for the paucity of blogging activity here as I'm well aware of Oscar Wilde's admonition that "conversation [...and one could include blogging in that...] about the weather is the last refuge of the unimaginative". I cannot ascertain where or when Oscar said this but it's copied ad infinitum on the web. I'm not sure I agree with Oscar on this point. Conversation regarding the weather oils social interaction, easing us into conversation with strangers, and has united us Brits in a collective misery at the recent vicissitudes of the wayward jet-stream. It's a decidedly British trait and should be included in the citizenship tests set by the Home Office.