How the Bed Bug Triage Tool Reaches a Result

What the tool is and is not

The evidence checker asks five questions and adds or subtracts points for each answer. It does not analyse photographs, and it does not diagnose bites. It cannot replace a pest professional or an expert ID.

We do not inspect homes or treat infestations.

Results appear instantly. The tool only knows what you tell it, so look carefully.

The five questions

The questions cover your specimen, its movement, its body shape, other signs and the location of the evidence. Each answer has a fixed point value. An answer of "not observed" or "unclear" adds no points.

Moreover, the same order underpins our guides on bed bug signs and bed bug lookalikes.

Specifically, dark spots count only when they appear with skins or eggs, because faecal spots can look like mould. A clear specimen photo helps you answer the body question, as shown in our guide to photographing an insect.

• A physical specimen adds 2 points
• Crawling adds 1 point; jumping or flying subtracts 5
• A flat, oval body of about 4–6mm adds 4
• A flea-like body subtracts 4; a hairy or hard-shelled body subtracts 3
• Dark spots, skins or eggs close together add 3
• Evidence near a bed or nearby furniture adds 1; pet bedding or a windowsill subtracts 1

Lookalike rules

Some answers override the total. A jump or a narrow body with big hind legs gives "More consistent with a flea". Flight or a hairy, hard shell gives "More consistent with another household insect".

Since these features do not fit a bed bug, extra points elsewhere cannot outweigh them. See bed bug versus flea for the reasoning.

Additionally, the result lists up to four reasons, so you can see which answers mattered most.

Result bands

A total of 8 or more gives "Strong feature match". A total of 4 to 7 gives "Possible match". Anything lower gives "Insufficient evidence".

However, none of these is a professional ID. Even a strong match should be confirmed by someone competent. The size option follows published adult sizes of roughly 4 to 6mm. The Natural History Museum gives 4 to 5mm and the NHS about 5mm, so treat the range as a guide.

For example, a specimen (2), crawling (1), a bed bug body (4) and signs near a hiding place (3) total 10. That gives a strong feature match.

Therefore, no result can reach a strong match unless the body-shape answer fits a bed bug. The other answers cannot reach 8 points between them. Bites, a single mark or an unclear sighting therefore never produce a strong result.

Why bites score nothing

Skin reactions are non-specific, vary between people and may appear after a delay. The CDC notes that marks usually appear from one to several days later, and in some people take up to 14 days. The tool therefore treats bites as a prompt to inspect and adds no points.

For the full explanation, read what bites can and cannot tell you.

Sources and limits

We rely first on the NHS, the Natural History Museum, the CDC and university extension services such as UC IPM. Where sources differ, we use cautious wording. We check details such as life cycle stages against those sources.

The tool cannot see your insect, so it cannot catch a misdescription. Our article on common bed bug myths shows why careful observation matters.

In short, health wording follows the NHS. Biology follows the Natural History Museum, the CDC and university extension services, and renting advice follows Shelter. Where published figures differ, such as adult size, we use a range.

Privacy and repeat results

The checker runs in your browser. Your five answers are never uploaded, stored or linked to an identity. The same answers always give the same result. Resetting the form clears the temporary state.

An optional enquiry form is separate and gets none of your answers. See the privacy page.