Short answer: The tube web spider (Segestria florentina) is venomous, not poisonous, and it can bite hard enough to pierce human skin. The bite is painful, but it is not considered dangerous to people. Adult females usually measure 13–22 mm in body length and males 10–15 mm, which makes this one of the largest spiders in Britain. Bites are uncommon and usually happen when fingers get too close to the spider’s tube in a wall.
Which spider is the “tube web spider”?
In Britain, “tube web spider” usually means Segestria florentina, sometimes called the green-fanged tube web spider. It belongs to the family Segestriidae. The name comes from its home: a silk-lined tube tucked into a hole in a wall, with straight threads fanning out from the entrance.
Two smaller relatives also live in Britain, Segestria senoculata and Segestria bavarica. They build similar tubes, so the common name is sometimes used loosely for all three. Other Segestria species are listed from places such as the United States, Japan and New Zealand, but this page focuses on S. florentina, the species most people mean when they search for tube web spider bites.
Australia uses a similar name, “tube spiders,” for a completely different group: burrowing spiders in the genus Misgolas. They are covered briefly near the end of this page.
Tube web spider bite: what to expect
Venomous, not poisonous
People often ask whether the tube web spider is poisonous. Strictly speaking, it is venomous: it injects venom through its fangs when it bites. “Poisonous” describes something that is harmful to eat or touch, which is not how spiders work.
Laboratory work on the venom of S. florentina has isolated two neurotoxins and one insect-specific toxin. That tells us how the spider subdues its insect prey. It does not, on its own, mean the venom is a medical risk to humans, and the British Arachnological Society describes the bite as painful but not considered dangerous.
Why bites happen
This spider does not go looking for people. It spends the day deep inside its tube and comes to the entrance at night. Bites are usually linked to a finger being pushed into or near the tube, for example while clearing ivy, repointing brickwork or poking at a hole in a wall. The spider reacts to anything that touches its trip lines as if it were prey, and its fangs are strong enough to get through skin.
What a bite feels like
Reported bites cause sharp, local pain at the time. The sources we checked do not describe serious or lasting effects. As with any bite or sting, some people react more strongly than others, and a small number of people can have an allergic reaction.
What to do after a bite
For people in the UK, the NHS advice for insect bites and stings is a reasonable guide:
- Wash the area with soap and water.
- Hold a cold pack wrapped in a cloth against it for at least 20 minutes to reduce pain and swelling.
- Raise the area if you can, and use a standard painkiller such as paracetamol or ibuprofen if needed.
- Avoid scratching, which can lead to infection.
- Ask a pharmacist if the area becomes hot, red, increasingly painful, swollen, or starts to ooze.
Get medical help if symptoms are getting worse instead of better, or if you feel generally unwell. Call 999 in the UK (or your local emergency number) straight away for signs of a severe allergic reaction, such as swelling of the lips, tongue or throat, difficulty breathing, or feeling faint or very confused.
Outside the UK, follow your local health service or poison center advice. A painful red mark is also not proof of a spider bite; many skin problems look similar, so if you did not see the spider bite you, mention that to whoever examines it.
For general guidance on bites from other species, see the Spider Bites & Danger section.
How big is the tube web spider?
According to the British Arachnological Society, adult female S. florentina measure about 13–22 mm in body length and males about 10–15 mm. Those figures are body length only, not leg span. The legs add noticeably to how large the spider looks, but a reliable leg-span measurement is not given in the sources we checked, so we have not included one here.
Its two British relatives are smaller, which helps when you are trying to work out which one you have found:
| Species | Female body length | Male body length | Typical look |
|---|---|---|---|
| Segestria florentina | 13–22 mm | 10–15 mm | Dark brown to black; iridescent green chelicerae (more bronze in males); adult females often have no clear abdominal pattern |
| Segestria bavarica | 10–13 mm | 9–11 mm | Dark brown to black with a darker version of the senoculata-style abdominal pattern |
| Segestria senoculata | 7–10 mm | 6–9 mm | Paler beige or grey abdomen with a dark, lobed central band; banded brown legs |
Males and young S. florentina can look quite similar to S. bavarica, so size and colour alone are not always enough for a confident identification.
How to identify a tube web spider
No single feature settles it, but several clues together point strongly to Segestria, and to S. florentina in particular. If you are new to this, our spider identification guide explains how to combine clues like these.
- Location: In Britain, it is mainly found in the south, often on old walls in towns.
- Six eyes, not eight: Segestria spiders have six eyes arranged in three pairs. You usually need a close photo to see this. Our page on how many eyes spiders have explains why eye count is useful.
- Leg posture: At rest, the front six legs point forward and only the last pair points backward. This is very typical of the family.
- Body shape: A long, cylindrical abdomen and a dark body overall.
- Green chelicerae: Adults have shiny green jaw parts, often the only thing visible at the tube entrance.
- The web: A neat hole in a wall with straight, separate silk lines radiating out like spokes. This is different from the fuzzy, matted silk around the holes used by lace-weaver spiders (Amaurobius).
- Season: Adults are usually found in summer and autumn.
Where the tube web spider lives
The World Spider Catalog lists S. florentina from Europe, North Africa, Jordan, Turkey, Ukraine, European Russia and Georgia, with introduced populations in Brazil, Uruguay and Argentina. It is generally regarded as a Mediterranean species that has spread beyond its original range.
In Britain it is thought to have arrived through shipping. In the mid-20th century it was known only from a few southern towns near the coast. Since then it has been found further inland, as far north as Oxford, and recorders believe it is still increasing. It remains scarce overall but can be common at individual sites.
Its favourite places are holes in walls, especially in older brick and stone buildings, and sometimes gaps under stones. It is mostly an outdoor spider on the outside of houses and garden walls, though it occasionally turns up indoors.
How the tube web spider catches prey
The tube is both a home and a trap. Inside the hole, the spider spins a silk-lined retreat. From the entrance, a set of long, straight threads runs across the surrounding surface. These act as trip lines.
At night the spider rests just inside the opening, with its front legs touching the threads. When an insect walks into one, the vibration tells the spider where it is. The spider darts out, bites, and pulls the prey back into the tube, sometimes within a couple of seconds. You can read more about different hunting strategies in our spider behavior section.
Living alongside tube web spiders
A tube web spider in a garden wall is not a sign that your home has a spider problem. It also eats insects that many people would rather not have around. If you would prefer to avoid any chance of a bite:
- Do not push fingers into holes in old walls, especially ones with radiating silk lines around them.
- Wear gloves when clearing ivy, repairing brickwork or moving stones.
- If one gets indoors, guide it into a container with a sheet of card rather than picking it up.
- Do not tease the spider out with fingers to get a photo. A close look is safer from a distance.
Not the same as Australian “tube spiders”
In Australia, the Australian Museum uses “tube spiders” for burrowing spiders in the genus Misgolas (family Idiopidae). These are a different group from Segestria: they are mygalomorph spiders, related to trapdoor spiders, and they live in moist forests of eastern New South Wales and south-eastern Queensland.
They are large brown spiders, about 15–25 mm in body length, and are best known for building a silk tube that sticks up above the ground from the top of their burrow, propped against a rock, stem or tree trunk. The tube can reach around 30 cm tall, and the burrow below continues down into the soil.
In Australia: large dark burrowing spiders are hard to tell apart, and some of them are funnel-web spiders. Australian health advice treats a bite from any big black spider as a possible funnel-web bite: call 000, keep the person still, and apply a pressure immobilisation bandage while waiting for help. Do not rely on the tube to tell you what kind of spider it is.
To explore other spider groups, browse Spider Types.
Frequently asked questions
Is the tube web spider poisonous?
No. It is venomous, meaning it injects venom through a bite. Its bite is painful, but it is not considered dangerous to people.
Can a tube web spider bite through skin?
Yes. Its fangs are strong enough to pierce human skin. Bites are still uncommon because the spider normally stays inside its tube.
Are tube web spiders aggressive?
They are quick to strike at anything that touches their trip lines or enters their tube, because that is how they catch prey. Outside that situation they are shy, especially in daylight, and they do not chase people.
How big is a tube web spider?
Adult females are usually 13–22 mm in body length and males 10–15 mm. That is body length only; the legs make the spider look larger.
Where do tube web spiders live in the UK?
Mainly in southern Britain, in holes in walls, especially in older buildings in towns. The species has been spreading and is now found further inland than it once was.
Why does the tube web spider have green fangs?
Adults have iridescent green chelicerae, the jaw parts that carry the fangs. The colour is one of the easiest ways to recognise an adult at its tube entrance, where the jaws are often the only part on show.
References
- World Spider Catalog. Segestria florentina (Rossi, 1790), and genus Segestria species list. Natural History Museum Bern. https://wsc.nmbe.ch/spec-data/40555
- British Arachnological Society, Spider Recording Scheme. Summary and notes for Segestria florentina. https://srs.britishspiders.org.uk/portal.php/p/Summary/s/Segestria florentina
- British Arachnological Society. Segestria identification sheet (three British species). https://britishspiders.org.uk/sites/default/files/2020-08/Segestria_online.pdf
- Sagdiev N.Zh., Valieva L.A., Korneev A.S., Sadykov A.A., Salikhov Sh.I. (1987). Toxic components of the venom of the spider Segestria florentina. Bioorganicheskaia Khimiia 13(8): 1013–1018. PMID 3675645.
- NHS. Insect bites and stings. https://www.nhs.uk/conditions/insect-bites-and-stings/
- Australian Museum. Tube spiders (Misgolas sp.). https://australian.museum/learn/animals/spiders/tube-spiders/
- healthdirect Australia. Spider bites. https://www.healthdirect.gov.au/spider-bites
