Is the cellar spider dangerous to people or pets?

No. The cellar spider (Pholcus phalangioides) is harmless to people and pets. It is not known to bite humans — its chelicerae (mouthparts) are small relative to human skin — and its venom poses no health risk. The often-repeated claim that it is 'the world's most venomous spider with fangs too short to bite' has no scientific basis whatsoever. No peer-reviewed study has ever demonstrated exceptional toxicity in cellar spider venom, and the claim was popularized by a television program, not by research. Cellar spiders are a complete non-event medically; their only inconvenience is the persistent webs in basement corners.

Is the cellar spider common in New Hampshire?

Yes — the cellar spider is one of the most common house spiders in New Hampshire and is found statewide, year-round. It thrives in the cool, damp, undisturbed conditions NH homes readily provide: unfinished basements, crawlspaces, fieldstone foundations, garages, and utility rooms. Because it stays active indoors all year and builds persistent visible webs, it is often the spider NH homeowners notice most. Its presence is not a sign of an infestation in any harmful sense — it is simply a permanent, harmless resident that has found suitable habitat.

How do I get rid of cellar spiders in my basement?

The most effective approaches are mechanical rather than chemical. Vacuum webs regularly — this removes eggs and adult spiders together in one step. Reduce basement humidity to below 50% with a dehumidifier, since cellar spiders specifically seek out damp conditions and populations thin out in dry environments. Seal gaps around sill plates, rim joists, and basement windows to block entry. Reduce clutter that provides undisturbed corners. Chemical sprays work temporarily but do not address the conditions that keep attracting spiders. For heavy recurring webs in a finished basement, a professional inspection can identify entry points and harborage that homeowners miss.

What does a cellar spider infestation mean — is something wrong with my home?

Not necessarily. Cellar spiders are drawn to conditions, not a sign that your home is unsanitary. Their presence means you have a cool, damp, undisturbed space — a common description of a New Hampshire basement or crawlspace — and that enough small insects are available to feed them. A very heavy population can indicate elevated moisture worth addressing for other reasons (mold, rot, structural integrity), but a few cellar spiders in a basement corner is simply what happens in most NH homes with unfinished basements. They are harmless residents, not indicators of a structural problem.

Is the 'world's most venomous spider' claim about cellar spiders true?

No — this is a persistent urban myth with no scientific foundation. The claim holds that cellar spiders have extraordinarily potent venom but fangs too short to pierce human skin. Neither part is supported by evidence. No study has ever demonstrated exceptional venom toxicity in Pholcus phalangioides, and their chelicerae, while small, are not categorically different from many other harmless spider species. The myth gained mainstream exposure on a television program but has never appeared in peer-reviewed research. Cellar spiders are harmless, and their venom is not considered medically significant by any authoritative source.

Is a cellar spider the same thing as a harvestman (daddy-long-legs)?

No — they are entirely different animals that share a popular nickname. A cellar spider is a true spider: it has two distinct body segments (cephalothorax and abdomen separated by a waist), produces silk, builds webs, and has venom glands. A harvestman is not a spider at all — it belongs to the separate arachnid order Opiliones and has a single fused body lump, no visible waist, and cannot spin silk or produce venom. Both are called 'daddy-long-legs' colloquially, which causes persistent confusion. Quick rule: if it is in a web, it is a cellar spider; if it is walking around with no web attached, it is likely a harvestman.

Why does a cellar spider shake or vibrate rapidly when disturbed?

The rapid vibrating or blurring motion is a defensive behavior called whirling. When a cellar spider is threatened — by a predator or by a human tapping the web — it spins itself at very high speed, creating a visual blur that makes it difficult for a predator to target accurately. The behavior is completely harmless and quite distinctive: if you tap near a cellar spider and it starts shaking violently in a blur, that motion is confirmation you have found Pholcus rather than another species. The movement stops as soon as the threat passes, and the spider returns to hanging inverted in the web.

Does the cellar spider eat other spiders?

Yes, and this is one of its more useful qualities. Cellar spiders actively hunt and consume other spiders — including, reportedly, spiders larger than themselves, which they subdue using their long legs to toss silk from a safe distance before moving in. Pest professionals sometimes note that a resident cellar spider population helps reduce other spider numbers naturally. They also eat small insects, mosquitoes, and other arthropods that wander into their webs. If you are inclined to tolerate spiders, the cellar spider is a reasonable one to leave alone — it is harmless and actively doing useful pest control work in your basement.

How do I keep cellar spiders out of my basement long-term?

Focus on three factors: moisture, entry points, and harborage. Dehumidify the basement to below 50% relative humidity — cellar spiders thrive in damp conditions and leave when it is consistently dry. Seal gaps around the sill plate, rim joist, and basement windows where spiders enter from the foundation exterior. Reduce undisturbed clutter that provides stable web-building sites. Knock down webs as you find them — without a stable web and food source, spiders relocate. These same steps reduce most basement spider species simultaneously. Chemical perimeter sprays add short-term control but need the environmental corrections to produce lasting results.

Long-bodied Cellar Spider · Pholcus phalangioides

SpidersNH resident

Cellar Spider (Daddy-Long-Legs) in NH: ID & Control

Also called Daddy-long-legs spider · Skull spider · Vibrating spider

The cellar spider — the long-legged, ghostly spider in your NH basement — is completely harmless, not known to bite people, and eats other insects and spiders. The famous 'world's most venomous with fangs too short to bite' claim has no scientific basis; it is a myth. Managing cellar spiders is mostly about reducing basement moisture and vacuuming webs.

At a glance

Body size: 6–10 mm (~grain of rice); legs ~5–6× body length; Missouri Department of Conservation
Bite risk: Not known to bite people; tiny chelicerae; insectidentification.org
NH status: Present statewide indoors; insectidentification.org
Diet: Insects and other spiders; Penn State Extension
'Most venomous' myth: False — no scientific basis; Penn State Extension

The short of it

Harmless, helpful, and absolutely everywhere in NH basements

The cellar spider (Pholcus phalangioides) — widely called the daddy-long-legs spider — is one of the most reliably encountered spiders in New Hampshire homes. It is also one of the most misunderstood. Its wispy, almost ghostly appearance, persistent webs in every basement corner, and the famous (and entirely false) claim about being 'the world's most venomous spider' combine to give it a reputation out of all proportion to its actual impact.

The reality: the cellar spider is harmless. It is not known to bite people, its chelicerae are not unusually small, and no scientific study has ever demonstrated unusual venom toxicity. The myth has no published peer-reviewed foundation. The spider's most distinctive feature is its extraordinary leg length — a body the size of a grain of rice suspended on legs that can span the width of a silver dollar — and its habit of vibrating the web rapidly when disturbed.

What the cellar spider is actually doing in your basement is eating other insects and spiders, including other species you would less prefer to have around. For most NH homeowners, the only real question is whether the webs in the corners are tolerable — and if not, how to manage them without overreacting.

Identify it

How to identify a cellar spider

Two features identify the cellar spider immediately: a body no larger than a grain of rice paired with legs that are disproportionately long and thin — typically five to six times the body length. Nothing else in your NH basement looks quite like it.

Species profile

Long-bodied Cellar Spider

Scientific name: Pholcus phalangioides
Family: Pholcidae
Size: Body 6–10 mm; legspan up to ~50 mm
Coloration: Pale gray, tan, or slightly translucent; small dark markings on cephalothorax; abdomen elongated and pale
Habitat: Basements, crawlspaces, garages, utility rooms, and fieldstone foundations — cool, damp, and undisturbed.
Active season: Year-round indoors; no seasonal retreat
Diet: Insects and other spiders, including spiders larger than itself
Reproduction: Female carries egg sac in chelicerae until eggs hatch; several egg masses per season
Lifespan: 1–2 years in favorable conditions

Present statewide in New Hampshire; found throughout the US and worldwide wherever suitable indoor habitat exists.

The tells — key ID features

Tiny pale body (grain-of-rice size) — the single most striking feature when seen in context with the legs.
Extremely long, thin, fragile-looking legs roughly five to six times the body length.
Loose, tangled, three-dimensional cobweb in ceiling corners and basement spaces.
Hangs upside-down in the web at rest.
Vibrates or whirls rapidly in the web when disturbed — a unique defensive behavior.
Pale gray or translucent coloration — almost ghostly in appearance.

Size, to scale

The insect

Body 6–10 mm; legspan up to ~50 mm

Compared to

Body roughly the size of a grain of rice; legspan can exceed a silver dollar

Looks bigger than it is

The extreme leg length makes the spider appear much larger than it is — the tiny body is the key to quick identification.

Is it actually this? — the confusion species

Harvestman (Opiliones — 'daddy-long-legs')

How to tell — A harvestman has a single fused body lump (no waist between body segments), cannot spin silk, and builds no web. If it is in a web, it is a cellar spider. If it is wandering the floor on long stalky legs with a tiny round body, it is a harvestman.

Crane fly ('mosquito hawk')

How to tell — A crane fly is a flying insect — it has wings, antennae, and no web-spinning ability. Often mistaken for a giant mosquito. Not an arachnid at all.

Common house spider

How to tell — Rounder, more compact abdomen; shorter, stockier legs; brownish mottled coloration; builds cobwebs at head height or in window frames rather than ceiling corners.

What you'll notice

Signs of a problem

Cellar spiders advertise themselves through webs far more than through direct sighting. These are the characteristic signs of a resident cellar spider population.

Loose, three-dimensional cobwebs in upper corners of basements, garages, and crawlspaces

What it means — The irregular, tangled structure in ceiling corners is classic cellar spider construction — not the orb web of a garden spider or the funnel web of a grass spider.

Multiple webs accumulating quickly after cleaning

What it means — Cellar spiders reproduce continuously indoors; fast web recurrence suggests an established population with good food supply and conditions.

A spider that shakes or blurs rapidly when the web is touched

What it means — The vibrating defensive behavior is unique to Pholcus and its relatives — if it shakes rather than fleeing, you have a cellar spider.

How much it matters

The real risks, calibrated

The cellar spider has no medical significance. It is not known to bite people and carries no venom of concern. The popular 'world's most venomous' myth has no scientific support.

Overall risk

Moderate

Cobweb accumulation (nuisance only)

Low risk

Onset: Ongoing while population is active

Persistent webs in basement corners and crawlspaces are the primary nuisance. No health risk is associated with cellar spider webs or presence.

Misidentification alarm

Low risk

Onset: Immediate

The 'world's most venomous' myth can cause unnecessary alarm. Cellar spiders are harmless; the myth has no scientific basis and should not drive treatment decisions.

What you can do

DIY — what works, what backfires

Cellar spider control is mostly mechanical — vacuum webs, reduce moisture, and seal entry points. Chemical treatment is rarely warranted and addresses only the symptom, not the conditions driving the population.

What actually works

Vacuum webs regularly — this removes eggs, hatchlings, and adult spiders together and is the most effective single step.
Dehumidify the basement to below 50% relative humidity; cellar spiders thrive in damp conditions and will reduce in population when humidity drops.
Seal gaps around sill plates, rim joists, and basement windows where spiders enter from the foundation.
Reduce undisturbed clutter in the basement — open shelving and empty corners have fewer suitable web sites.

What backfires

Don't fog or panic-spray for cellar spiders — they are harmless, and aerosol treatment without addressing moisture and entry points produces only temporary results.
Don't mistake a harvestman (a wandering, web-free arachnid with a fused body) for a cellar spider and over-treat.
Don't assume heavy cobwebs mean a dangerous species — in a NH basement, it almost always means cellar spiders, not anything medically significant.

Local Context

Cellar spiders in New Hampshire homes year-round

Cellar spiders thrive in virtually every New Hampshire basement and crawlspace because the conditions here are ideal: cool, damp, and undisturbed. Unfinished basements, fieldstone foundations, utility corners, and rim-joist cavities are prime habitat. Unlike many spiders that are seasonal, the cellar spider is active year-round indoors — there is no season during which they retreat outdoors. In southern NH, the same features that make older homes energy-inefficient — gaps around sill plates, uninsulated rim joists, open crawlspaces — also create ideal cellar spider harborage.

Peak season

Year-round indoors; no seasonal retreat

You might actually have

Common house spider (rounder body, corner webs at head height)
Wolf spider (large, ground-hunting, no web)
Harvestman / daddy-long-legs (not a spider — fused single body, no web)

We serve these communities

ManchesterNashuaConcordBedfordDerrySalem

Hillsborough · Rockingham · Merrimack Counties

NH-licensed applicator · #782664
Same-day service
Family-owned since 2017

Service Area Map

Southern New Hampshire

When it's past DIY

When to call a pro for cellar spiders

A few cellar spiders in a basement corner require no professional intervention. Heavy recurring populations in a finished basement — especially where webs are becoming aesthetically problematic or the moisture issue driving them has not been identified — can benefit from a professional inspection.

Signals it's past DIY

When to call a pro

Heavy recurring cobwebs in a finished basement that return within days of cleaning.
You want the moisture and entry-point conditions professionally identified and corrected.
You are unsure of your identification and want confirmation of which spider species you actually have.

Keep them out — prevention

Dehumidify to below 50% RH

A dehumidifier in the basement is the single most impactful step — cellar spiders need damp conditions and will naturally reduce when relative humidity drops below 50%.

NH-specific

Seal sill plate and rim-joist gaps

Foam or caulk around the sill plate and rim joist blocks the primary entry paths from the foundation into the basement — this reduces all basement spider species, not just cellar spiders.

Knock down webs on a routine schedule

Without a stable web, cellar spiders relocate. Regular vacuuming of basement corners — even monthly — keeps populations from establishing at high density.

Not sure it's a long-bodied cellar spider?

A licensed NH technician can confirm the species and tell you honestly whether it's a DIY fix or a job for a pro — free inspection, same-day service across Southern New Hampshire.

Get a Free Inspection (603) 785-0118

Common Questions

Frequently asked questions

Sources(3)

[1]
InsectIdentification.org — Long-bodied Cellar Spider
not known to bite people; NH statewide presence
referenceverified 2026-06-30
[2]
Penn State Extension — Long-bodied Cellar Spider
in no way harmful ('most venomous' myth false); diet including other spiders; common in cellars and garages
extensionverified 2026-06-30
[3]
Missouri Department of Conservation — Long-bodied Cellar Spider
habitat; behavior; identification; harmlessness; body size 6–10 mm; leg length ~5–6× body
govverified 2026-06-30

Written & reviewed by

Verified

Daniel Brady

NH-Licensed Pesticide Applicator · License #782664 (NHDAMF, RSA 430)

Daniel Brady is the New Hampshire–licensed applicator behind Anchor Pest Services, a family-owned pest control company serving the Manchester area since 2017.

Verify license

Last updated 2026-06-30

New Hampshire pest control

Dealing with long-bodied cellar spiders in your home?

Anchor Pest Services identifies and handles long-bodied cellar spider problems across southern and central New Hampshire. Family-owned since 2017, NH license #782664.