# Glow-worm — Facts, Threats & Conservation

*Lampyris noctiluca (Linnaeus, 1767) in Britain; Arachnocampa luminosa (Skuse, 1890) in New Zealand — unrelated animals sharing one name*

> Glow-worm is not one animal: in Britain and Europe it usually means the beetle Lampyris noctiluca, whose larviform female glows green to attract mates; in New Zealand it means the fungus gnat Arachnocampa luminosa, whose larvae glow in caves to lure prey into silk traps.

**IUCN status:** Not Evaluated — European glow-worm declining in parts of Britain; New Zealand cave species locally protected  ·  **WARN range:** Britain and Europe — Lampyris noctiluca, New Zealand — Arachnocampa luminosa in caves and ravines

## Quick facts
| Fact | Value |
| --- | --- |
| European animal | Beetle Lampyris noctiluca |
| New Zealand animal | Fungus gnat larva Arachnocampa luminosa |
| European glow | Green — adult female abdomen |
| NZ glow | Blue-green — predatory larva |
| Purpose | Mate attraction (EU) versus prey lure (NZ) |
| Name accuracy | Neither is a worm |

## Scientific classification
- **Kingdom:** Animalia
- **European — Phylum:** Arthropoda
- **European — Class:** Insecta (Coleoptera: Lampyridae)
- **European — Species:** Lampyris noctiluca
- **New Zealand — Class:** Insecta (Diptera: Keroplatidae)
- **New Zealand — Species:** Arachnocampa luminosa
- **Shared name:** Glow-worm — two unrelated bioluminescent insects

## Conservation status
- **Status:** Not Evaluated
- **Population:** No global estimate; local declines reported for Lampyris in Britain
- **Trend:** Decreasing in parts of Europe — habitat and light pollution
- **Assessed:** Lampyris not globally Red-Listed
- **CITES:** Not listed
- European glow-worm declines are documented in national monitoring though the species lacks a global IUCN assessment. Cave tourism management protects New Zealand populations locally.

## Key facts: Glow-worm
- Glow-worm is a common name applied to unrelated bioluminescent animals, not a single species.
- European Lampyris noctiluca is a firefly beetle; the glowing adult female is wingless and larva-like.
- New Zealand Arachnocampa luminosa is a fungus gnat; only the larva glows, hanging silk snares in caves.
- European males fly and are not luminous; they find females by the green glow on grassland banks.
- Both use bioluminescence but for different purposes — mating signal versus prey attraction.
- European glow-worms have declined in parts of Britain, linked to habitat loss and light pollution.

## Britain and Europe: the beetle that is not a worm
Lampyris noctiluca belongs to Coleoptera, the beetles, in the family Lampyridae — the same broad group as fireflies, though European glow-worms behave differently from the flashing American fireflies most people picture. The larva is a predatory grub feeding on snails and slugs. The adult female retains a larval appearance — soft wingless body — and climbs vegetation at night to glow continuously from the last abdominal segments.

Flying males, smaller and winged, locate her by that green light. After mating she extinguishes the lantern and lays eggs. Adult females do not feed; the glow is pure reproductive advertising. Grassland banks, hedgerows and railway embankments with snail populations are traditional sites; loss of rough grassland and artificial light at night are among the pressures cited in British decline reports.

## New Zealand: the cave larva fishing with silk
Arachnocampa luminosa is a dipteran — a true fly in the family Keroplatidae. Only the larva bioluminesces. It builds mucus tubes on cave ceilings or overhangs in ravines, then dangles sticky silk threads tipped with mucus droplets. Insects attracted to the blue-green glow become entangled; the larva reels them in.

Tourism to glow-worm caves — Waitomo is the famous example — depends on these larvae. Disturbance, light pollution and habitat change affect populations locally. The life cycle is fly-like: larva, pupa, short-lived adult gnat that does not glow. Calling it a worm misleads on every count except shape in the dark.

## Bioluminescence — same word, different chemistry and purpose
Both animals produce cold light through luciferin-luciferase reactions, but the evolutionary origins of their systems differ because beetles and flies are not close relatives. In Lampyris the light is a mate beacon — maximal at female peak fertility. In Arachnocampa it is a trap lure — maximal where flying insects are dense.

Light pollution interferes with the beetle's signal more than with the cave fly's, because cave systems are dark by definition while European grasslands are increasingly lit. That asymmetry shapes conservation advice: reduce unnecessary outdoor lighting near known glow-worm banks; protect cave access regimes that limit vibration and torch glare.

## Why one name covers two animals
English colloquial names often track appearance over ancestry. A elongated glowing creature in grass and a dangling glowing thread in a cave both earned 'worm' before children learned phyla. Disambiguation is now a search-engine problem: queries from Britain and New Zealand return the same headword for different animals.

This page treats both because that is what the name requires. If you are on a chalk bank in Sussex on a June night, you want Lampyris. If you are in a Waitomo boat, you want Arachnocampa. Neither is a worm.

## What WARN does
WARN publishes free invertebrate education that disambiguates shared common names before answering biology questions. Glow-worm is a high-traffic example of one English word mapping to two unrelated animals — answering without naming which one fails half the readers.

If this guide helps you understand wildlife and the pressures it faces, a gift to WARN supports habitat protection and free public education in our partner countries.

## Frequently asked questions: Glow-worm
### What do glow-worms eat?
European glow-worm larvae (and larviform adult females do not feed as adults) eat snails and slugs as predatory beetle grubs. New Zealand glow-worm larvae eat small insects caught on sticky silk threads, lured by the larva's bioluminescence.

### Where do glow-worms live?
European Lampyris noctiluca lives on grassland banks, hedgerows and rough pasture in Britain and Europe. New Zealand Arachnocampa luminosa larvae live in damp caves, tunnels and forest ravines, especially on the North Island.

### Are glow-worms dangerous?
Neither animal poses any meaningful risk to humans. European larvae may bite small prey; New Zealand larvae are tiny and confined to caves and overhangs. Tourism access rules protect cave populations from disturbance.

### How long do glow-worms live?
European glow-worm larvae live one to two years before pupating; adult females glow for a few weeks to attract mates. New Zealand larvae live roughly nine months before pupating; adult fungus gnats are short-lived and do not feed.

### How big are glow-worms?
European adult females reach roughly 15–20 mm — larva-like and wingless. New Zealand larvae are a few centimetres long when mature, including the silk fishing lines that extend further into the cave darkness.

### Why are there two different glow-worms?
English reuses names across unrelated animals. Britain's glow-worm is a beetle; New Zealand's is a fungus gnat larva. Both glow, but they are not closely related and should not be treated as one species in reference material.

## Sources
- [Buglife — glow-worm decline in Britain](https://www.buglife.org.uk/bugs/bug-database/glow-worm/)
- [Te Ara — New Zealand glow-worm](https://teara.govt.nz/en/glow-worms)

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Full guide: https://worldanimalrescuenetwork.org/wildlife-guides/glow-worm