The glow worm is a medium to large sized invertebrate that is famous for having a green and yellow coloured light on the end of it’s tail.
Glow worms are found inhabiting dense woodland and caves around the world with the exception of the Americas and glow worms are one of the few insects that are found inside the colder Arctic Circle. Glow worms are nocturnal animals which means that they are active during the dark night which is when their glowing rears can be seen.
Glow worm is the common name for various different groups of insect larva and adult larviform females which glow through bioluminescence. Glow worms may sometimes resemble actual worms, but all are insects as one species of glow worm is a type of fly but most glow worms species are actually beetles.
It is only the female glow worms that actually glow as they spend around 2 hours every night in the mating season with their bottoms in the air, trying to attract a mate. The male glow worms are attracted to the glowing object in the foliage but have also been known to be attracted to man-made lighting such as street lights.
Glow worms are most commonly seen in the UK between June and October and their green-lit tails tend to show up most clearly when the sun goes down at dusk. Legend says that early humans used to use glow worms to mark paths and provide light in huts. Glow worms were thought to have some kind of magical power and so people would also use the glow worm in medicines.
Glow worms are omnivorous animals but they tend to have a very meat-based diet. Glow worms predominantly prey on snails and slugs which make up the majority of the glow worm’s diet. Glow worms also prey on other insects and small invertebrates.
Due to their small size and the fact that they glow in the darkness, glow worms have numerous natural predators within their environment including spiders, large insects, birds, reptiles and centipedes.
Typically, the female glow worms lays between 50 and 100 eggs in moist areas, over a period of a few days. The tiny glow worm eggs are yellow in colour and can take between 3 and 6 weeks to hatch depending on the climate (the warmer it is, the faster the glow worm eggs will hatch).
Glow worms are considered to be an animal species that is threatened with extinction as the glow worm population numbers are drastically decreasing. The main reason for the lower number of glow worms is thought to be the expansion of human civilisations. Glow worms are known to be particularly vulnerable to changes in their environment including habitat loss, noise and pollution.
Quick Glowworm Facts
Common Name: Glow Worm
Scientific Name: Arachnocampa luminosa
Size: 2.5-5.0cm (1-2in)
Number of Species: 12
Average Lifespan: 5 months
Conservation Status: Threatened
Colour: Black, Brown, Yellow, Green, Red
Skin Type: Shell
Favourite Food: Snails
Habitat: Undisturbed woodland and caves
Average Litter Size: 75
Main Prey: Snails, Slugs, Insects
Predators: Spiders, Birds, Centipedes
Special Features: Long, flat body and green light on tail
Glowworm Questions and Answers
WHAT IS A GLOWWORM?
A glowworm is the larvae stage in the lifecycle of a two-winged insect. It grows as long as a matchstick and looks a bit like a maggot. There are many different types of glowworm. The one we have in New Zealand is arachnocampa luminosa. ‘Arachno’ means spider-like, which refers to the way glowworms catch flying insects like spiders do. ‘Campa’ means larva and ‘luminosa’ means light-producing.
WHY AND HOW THEY GLOW
A glowworm uses its glow to attract food and to burn off its waste. It’s tail glows because of bioluminescence, which is a reaction between the chemicals given off by the glowworm and the oxygen in the air. This chemical reaction produces light, which the glowworm can control by reducing the oxygen to the light organ. Insects fly towards the light and get stuck in the sticky lines that the glowworm hangs down to catch food. Glowworms also use their glow to put other creatures off eating them.
WHY THEY ARE FOUND IN CAVES
Glowworms can survive only in very damp, dark places where their light can be seen. They need a ceiling that is fairly much horizontal from which they can hang their sticky feeding lines, and a sheltered place where wind does not dry them out or tangle their lines. The Waitomo Glowworm Caves provide a perfect environment with an abundance of insects brought into the cave via the river.
The Glowworms Lifecycle
The lifecycle of a Glowworm is in four stages and takes about 11 months. Eggs are laid in clutches of 30-40 on walls and ceilings. Immediately on hatching from the egg, the larvae emit a light, build a nest, put down lines and feed. Sticky substances on the lines trap insects and these are drawn up and devoured.
The larvae stage is the longest phase in the creature’s life and lasts around nine months. It then turns into a pupa in a cocoon and emerges as a two winged flying insect, which looks like a large mosquito.
The adult fly lives no longer than a few days as it has no digestive system and so cannot eat. Instead it uses this time to mate and lay eggs. The glowworms found in the Waitomo Glowworm Caves is a species unique to New Zealand.
The female fly lays around 120 small spherical eggs. Within around 20 days the young larvae hatch from the eggs and crawl away.
After hatching the young larvae build a nest, put down lines and feed. Sticky substances on the feeding lines trap insects and these are drawn up and devoured. Even at this small size, less than 3 millimetres long, they emit a strong visible light and slowly grow over 9 months to the shape and size of a matchstick.
The pupa is the same as the cocoon stage in the butterfly lifecycle; it is the stage between the larva and the adult fly. This will last about 13 days with the pupa suspended by a thread from the ceiling.
The adult glowworm looks like a large mosquito. They have no mouth and their only function is to reproduce and disperse the species. Usually a male is waiting for the female to emerge from the pupa, mating takes place immediately and the cycle continues. Adult glowworms live no longer than a few days
More Information on the Glowworm
The Glow-worm herself (it is always the females who do the serious glowing) has very poor eyesight, so with a bit of care it should be possible to approach to within a few inches of her for a closer look without her being aware of you. At this range you can see that the light comes from two broad bands and two small dots on the underside of her tail, which she twists over so that it can be seen from above. Far from being a worm, she is really an insect, a beetle (Lampyris noctiluca) belonging to the firefly family. She has no wings, which means that she can’t go off in search of a mate, so instead she uses her light to flag down passing males as they patrol overhead.
If you inspect enough females you should eventually come across one who has managed to attract a partner (these often appear dimmer than lone females, partly because the males tend to obscure the light and partly because the female normally switches off her display once she starts to mate). In fact Glow-worms are extremely broad-minded in their mating habits and in extreme cases it is possible to find the female submerged beneath a scrum of as many as eight males, each trying to prise the others off. Seeing a male on his own you would be hard pushed to recognize him as belonging to the same species: he has a full set of wings and wing-cases and looks like a proper beetle. His huge eyes cover most of his head and allow him to home in on the female’s light, and a transparent visor protect them from knocks during his travels.
Neither the male nor the female Glow-worm have any mouthparts, so they can’t feed and their brief adult lives are a race to meet, mate and lay eggs. Most males are dead within a few days of mating and very few females reach the ripe old age of three weeks. A female can’t afford to waste precious time and energy on travelling, so she rarely strays more than a yard or two from where she first emerged. Having mated, she lays about 50 – 150 small, round, faintly-glowing eggs, but by the time they hatch about a month later she will have long since died.
When it first hatches from its egg the Glow-worm larva is almost pure white, but it soon darkens to a distinctive soot-black, with cream spots at the corners of each segment of its body. Like most children it is very picky about what it will eat, accepting only slugs and snails. It nips its prey with sharp, sickle-shaped jaws that inject a poison to paralyse and digest the victim, dissolving it into a lumpy soup that the larva can lap up. In this way the young Glow-worm may polish off as many as seventy slugs and snails during the course of its childhood.
Again like many children the young Glow-worm is a messy eater, but unlike most children it will clean itself up after each meal. A special organ stowed in the tip of its tail can be opened out into a cluster of tentacles, which the larva uses to sponge down its head, legs and body, mopping up any remaining blobs of liquefied snail.
The Glow-worm larva itself seems to have very few enemies to worry about. Its body is thought to contain a poison that protects it against predators and it uses pulses of light from two small spots beneath its tail to warn would-be attackers that it is not to be messed with.
In fact it may be that the Glow-worm’s distant firefly ancestors first evolved their light as a warning signal and only later started using it as a way of attracting a mate. To repel predators with poor eyesight, such as ants, the larva has a row of white glands down each side of its body which produce an unpleasant taste.
A typical Glow-worm larva takes two years to grow up, hunting in the summer and passing two winters in hibernation below ground or under logs or stones. For most of its childhood it is strictly nocturnal and rarely seen, but in the spring of its final year it will change its habits and start to wander about in broad daylight, perhaps looking for new habitat or seeking out a good spot in which to pupate. Once it has found a safe retreat it sheds its skin for the last time and passes the next week or two as a pupa. Finally, two years after being born, the Glow-worm re-emerges as an adult, ready to complete its life cycle.
Fun Facts on the Glowworms
> Glowworms are not worms, but insects.
> The adult glowworm cannot eat because it has no mouth.
> It can take the female up to 24 hours to lay her eggs.
> A male adult glowworm lives for 5 days, but the female only lives for 2 days.
> The larva stage of the insect is the only stage that eats anything.
> The larva can last for several months without eating.
> The glowworm larva is more like a maggot than a worm.
> The female lays about 130 eggs and dies immediately afterwards.
> Glow worms are cannibals!.
> The female glow worm is generally larger than the male.
> They do not have to look for food – it comes to them. It is attracted by their glow.
> They catch their food in sticky fishing lines that they hang down.
> They eat meat, usually other insects.
> A glowworm lives for 10 – 11 months from birth to death.
> A glow worm spends up to 7months of its life glowing in the larva stage.
> The glow worm fly (adult) is a poor flyer.
> Glow worms live in dark , damp places like caves and river banks.
> The Māori name for the glowworm is “pura toke” (blind or one-eyed worm).