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Glow worms: Britain's brightest beetle

Updated Wednesday, 5th September 2012

Steve Hussey from the Devon Wildlife Trust discusses glow worms, their habitat, and the impacts on their population

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In this extended interview from Saving Species, Steve Hussey from the Devon Wildlife Trust looks for one of our most enigmatic and enlightening beetles: the glow worm. Has Devon's glow worm population declined since the last survey was completed in 1999?

A glow worm glowing Copyrighted  image Icon Copyright: Devon Wildlife Trust A glow worm lives up to its name


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Presenter:  Well on an overcast but warm yet slightly windy evening I find myself in the County of Devon and quite near to Exmouth actually on the Bystock Nature Reserve run by the Devon Wildlife Trust.  And with me is Steve Hussey of the Devon Wildlife Trust.  You’ve got a group of people here, and we can just see them, they’ve moved away from us at the moment.  This is an official glow worm walk this evening.  Steve, this is classic glow worm habitat?

Steve:  It is.  They need open country; they need grassland.  They need places that haven’t been overgrazed; that do have some grazing; that haven’t been sprayed with herbicides and pesticides; that haven’t been tidied up.  So much of our countryside has been tidied up.  This place has been left.  Not totally left, it’s managed, but it’s managed sympathetically with a light hand, and that’s good for glow worms, as it is with so much other wildlife.

Interviewer:  Describe what we’ve got in front of us that’s so good for glow worms?

Steve:  Well we’re standing at the very top of what is an old fashioned wild flower meadow.  It’s unfortunate that there aren’t many of those left, and the meadow sweeps down into heathland, another landscape that’s really taken a battering over the last century or so.

Interviewer:  Now you’re running a very special campaign aren’t you on the glow worms, how rare is this animal?

Steve:  Well that’s one of the things we’re trying to find out.  We did a similar survey 12 years ago, so we want to see how our glow worms are faring in the County of Devon today.  They’re scattered, I think is the best way to put it, throughout the South of England and throughout the whole of the UK.  The South of England is the main place for them.  Devon is not a bad county as its populations, but they were once much more widespread. 

Interviewer:  We’ve got a group of people gathered around here, have they got one?  Oh excellent!  Now I’m stood probably about five metres away from that, and that to me Steve that is really standing out.

Steve:  Yeah. 

Interviewer:  That’s amazing.

Steve:  Well you can hear the gasps from other people.  I mean it’s an unnatural thing, that’s why there’s so much folk lore surrounds this species.  Not many things give off light, they do naturally, and there we see it.  I mean they need to have a bright enough light to lure in a male, and those males can pick them up from 50, 60, 70 metres away.

Interviewer:  So how is it giving off that light, what’s going on?

Steve:  Well it’s bioluminescence.  It’s produces a chemical called luciferin, and that oxidises with the air around it, and that gives off this pale green yellow light.

Interviewer:  Amazing, that’s just absolutely stunning.  And we can only see one, we can’t see any more.

Steve:  There should be others nearby; you don’t, you rarely get a single glow worm by itself.  Some years are good glow worm years, you’ll see lots of adults displaying like this, and then perhaps nothing the next year or not many the next year, that’s because the glow worm has a two year larval life cycle.  So the lavae don’t glow generally, they can put out a pale glow for brief periods of time, but generally they don’t glow strongly or for long periods of time.  So it might go two or three years before you see that colony erupt again with lots of lights. 

Interviewer:  Right, so this glow worm’s not moving at all is it?  It doesn’t seem to be.

Steve:  No.

Interviewer:  The light’s not moving.

Steve:  She can’t fly, the males can.  So she needs to be static but she needs to be on display.  So that’s why she’ll get to the top or close to the top of a grass stem, she’ll put her backside in the air, it’s the last two or three segments of her abdomen that will shine, and that’s her signal for the males that can fly.  During the day she’ll look to go underground or tuck herself down in amongst the grass stems, simply to get out of the way of being predated. 

Interviewer:  Okay, let’s go and see if we can find some more, because that one appears to have, can I say switched off?

Steve:  They can switch off.  What it’s probably done actually is our eyes have got used to people’s torch lights and camera flash bulbs, so they can turn off and they can dull their lights, but I’m sure we’ll find others if we go through the gate.

Interviewer:  Yeah let’s go.

Now we’ve just come in through the gate and straightaway I’m attracted towards the tiny lime green light on the ground.

Steve:  They do give off a glow, there’s no doubt about it.  And once you get your eye in you can see them.

Interviewer:  How long do they actually glow for?

Steve:  A female like this would probably glow for no more than two perhaps three weeks at the most.  Once she’s found her mate, bred, laid her eggs, she’ll die, and the male will die as well.  In fact they spend more time, two years or more, as lavae.  They don’t glow very often as lavae.  They’re waiting for this moment, this climax when they become this glowing wonderful fairy sort of presence in our countryside.

Interviewer:  It’s a beetle isn’t it?

Steve:  It is a beetle.  Yeah it’s not a worm at all.  So it’s a bit like a wood louse, a big wood louse, about two, two and a half centimetres long.  If you saw one during the day you wouldn’t think anything of them, but just look at them tonight, they’re real show offs at night.

Interviewer:  Give me a close look.  What I want you to do is actually pick that up.

Steve:  Yeah, let me see if I can pick it up.

Interviewer:  It’s not going to harm the animal is it?

Steve:  No, it gives off no heat; it’s a very efficient light.  It’s 90-odd percent of the energy that it creates goes into producing the light rather than any warmth.

Interviewer:  And Steve’s very gently picking it up.

Steve:  There we go.

Interviewer:  Oh wow, in the palm of his hand, actually lighting the palm of your hand up.

Steve:  Just about yeah.

Interviewer:  And we can, though it’s very dark we can actually make out very good description you gave here earlier that almost wood louse, static wood louse.

Steve:  It is.

Interviewer:  It’s not going to move very fast is it?

Steve:  It’s not moving.  No, she can’t fly, she’s going nowhere.  What she does is move slowly to the top of a grass stem, she puts her head down and puts her backside up into the air, and it’s the last two segments of that abdomen that shine out in her message to passing males, here I am and I’m ready to mate. 

Interviewer:  Well this is absolutely incredible: I’m walking across short grass field.  Steve, it’s just like it’s, it’s just like the field is beginning to switch on in front of me.

Steve:  Yeah.

Interviewer:  I don’t think I've ever seen so many glow worms, and in the middle of a field.

Steve:  No, and I think it’s early evening as far as these glow worms are concerned, I think there are going to be more as we just stand here.  There must be what 25, 30 as we speak?

Interviewer:  Let’s go down, I want to get a close encounter with a glow worm.  What I’m going to do is I’m going to put my hand really close to it, and I’m going to see, it’s really quite dark now, that’s actually lighting my hand up.

Steve:  It is yeah.  I mean there are I think perhaps apocryphal stories of people reading by the light of glow worms, but I think you’d need a fair few, and of course we’re saying don’t move them, don’t touch them or whatever, but no I mean they give off a light and it’s a bright light, it needs to be, it needs to attract males. 

Interviewer:  Yeah, and obviously we’ve already said that this is the female, and the males, where are the males now?

Steve:  Well they’ll be flying around, and they’ll be looking to locate with a female and then come down and mate.  And once they do mate, then that female will stop glowing.  She’ll lay her eggs in amongst the grass here, and then she’ll die, and the male will die very quickly afterwards.  So in this stage of their life, their adult life, they’ll only live for two weeks. 

Interviewer:  I’m just going to, I’m just trying to take all this in because this is absolutely incredible.  I don’t think I've seen a field like this for a very long time that’s absolutely so full of glow worms.  Obviously you’ve now got all these people are now counting the glow worms in this field, what’s going to happen to all that data?

Steve:  Well we took a similar survey 12 years ago, so the first thing we need to do is compare today’s results with the picture for glow worms 12 years ago.  We think they’re declining but we need to know more about that picture, where they’re declining if they are declining, where they’re doing badly, where they’re doing well.  The other thing we can do with the data that we collect is tell local people, local parishes that have got glow worms where they’ve got them and how to protect them.  So that might be as simple as not mowing, not tidying up waste spaces, not spreading pesticides.  But people don’t know that they have glow worms locally to them, once they do know then they want to protect them and we can help them do that.

Interviewer:  Because it’s a very popular species isn’t it?  I mean look at all these people around us.  I mean we can see people going down everywhere across this field actually counting these glow worms.  And is there any chance of actually picking a glow worm up?

Steve:  Yeah, you can yeah, as long as we’re not going to move it out of the field, that’s the main thing.

Interviewer:  No, I can’t actually see the body.  Do you want to do it Steve?  Steve’s just gently picking it up between two fingers, wow, and it’s now in the palm of his hand.  And it’s actually lighting the central part of your hand.

Steve:  Yeah.

Interviewer:  And that’s like a lime green light isn’t it, coming off of it.

Steve:  Yeah, it’s a pale green light.  I mean it’s what Gilbert White at Selborne fame talked about it’s her fiery amorous light.  You know, it’s there to attract a mate, that’s all it does.  I mean it’s the second or third segment of her backside that’s shining out, it’s a message of love.

Interviewer:  Why is this species so important?

Steve:  Well it’s a good indicator of a healthy ecosystem that this habitat where we are is a healthy one and supports a diverse amount of wildlife.  If they weren’t there then you can bet your bottom dollar that other species wouldn’t be there that should be there. 

Interviewer:  That’s another one of those indicator species.

Steve:  Exactly, and they were a common and should be again a common species that we find around us.  Why shouldn’t every young child have one of these glow worm communities in their own community, close to them - I did as a child.  Unfortunately that experience has gone from many people’s lives; a little light has gone out of their lives literally.

Interviewer:  Now all the people we were with, they’re now spread out across this field, they’re all counting glow worms, what’s going to happen to all that data Steve?

Steve:  The first thing we’ll do is compare the data that we get from this year’s survey with that that we got twelve years ago to see how glow worms have done over the last ten, twelve years.  Our suspicion is that they’re struggling as a species but we need to know that and have some evidence.  We’ll also feed that data into a national survey that’s going on.  But what we’ll also do is tell the places, the parishes that have glow worms in Devon that they’ve got them.  They may not know that, and let them understand that there are simple measures they can take to help their local glow worms.  It might be as simple as not cutting so often grass verges; it might be not spraying them with herbicides, pesticides.  So it’s about letting people know that they exist and then helping them to look after them.

Interviewer:  People then taking ownership, isn’t it?

Steve:  Exactly, and you can see the reaction of people around you tonight, you know, there’s that real wow factor about this species.  People do want to take ownership of it and look after these things; they’re wonderful things to see.


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