Fleas

Signs of fleas in the house, and what flea eggs and flea dirt look like

How to confirm fleas before you treat: the white sock test, what flea dirt, eggs and larvae look like in millimetres, and why fleas turn up in houses with no pets.

The short answer

The quickest signs are itchy bites around your ankles, a pet scratching, and fine black specks in pet bedding or on the carpet that turn red on damp white paper, because they are dried blood. Walking slowly across the carpet in white socks will often pick up adults. Eggs and larvae are there too, pale and from half a millimetre to five millimetres long, but hard to see unless you look. Confirming first is what makes flea treatment for Auckland homes work.

At a glance

What each sign looks like, and where to look

What each sign looks like, and where to look
Sign	Size and look	Where to look	What it tells you
Adult flea	1–3 mm, reddish brown to black, flattened side to side, jumps	On the pet, on white socks, at ankle height	Fleas are present now
Flea dirt	Fine black specks like ground pepper, red smear when wet	Pet bedding, the pet's coat, the sofa where it sleeps	Adults are feeding; larvae have food here
Egg	About 0.5 mm, white, oval, smooth; drops off the animal	Where the pet sleeps and rests	Breeding is happening at this spot
Larva	1.5–5 mm, pale, legless, bristly, dark gut, avoids light	Deep in carpet pile, board gaps, under cushions	The infestation is established
Cocoon	Small, coated in dust and fibre, near invisible	Base of the carpet, cracks, under furniture	Fleas will keep appearing after treatment

The first signs of fleas

Most households notice fleas in the same order: bites around the ankles, then a pet scratching or grooming more than usual, then black specks in its bed, and finally fleas seen jumping on pale carpet or on someone's socks. A pet that is not scratching can still be carrying fleas, because some animals barely react when only a few are on them, so the absence of scratching proves very little.

The cat flea, Ctenocephalides felis, is the one behind almost all of this in New Zealand homes. People often search for dog fleas, but the cat flea is commonly found on dogs as well, so the signs below are the same whichever animal you have. Two simple tests turn a suspicion into an answer.

The white sock test and the damp paper test

Pull a pair of white socks high up over your trousers and walk slowly through the carpeted rooms, pausing now and then where the pet usually lies. Adult fleas jump onto the socks and show up as dark specks against the white. For the second test, collect some of the black specks from the pet's bed or coat and drop them onto damp white paper. Flea dirt dissolves into reddish brown smears, because it is digested blood, while ordinary dirt stays grey or brown.

Both tests take about five minutes and cost nothing. A positive damp paper test on the pet's bedding is about as definite as home identification gets, and where you found the specks is where the eggs will be too.

What flea eggs look like

Flea eggs are tiny white ovals about half a millimetre long, smooth and dry, and they slide straight out of the animal's coat, so they are almost impossible to spot on carpet or bedding. They land wherever the animal sleeps and rests, which puts most of them in the pet's bed, on the sofa cushion it favours and in the sunny patch of floor by a door. A female lays twenty to fifty a day, so finding even a few means many more.

Because the eggs are so hard to see, flea dirt is the better thing to look for. The two turn up in the same places, since both fall off the animal while it rests.

What flea larvae look like

Flea larvae are pale, legless, bristly grubs between 1.5 and 5 mm long, with no eyes and a dark line of gut showing through the body. They avoid light, so they live deep in the carpet pile, in the gaps between floorboards and under cushions, where they feed on the dried blood that adult fleas pass as droppings.

Seeing a larva is unusual even in a heavy infestation. If you part the carpet pile near the pet's bed with your fingers and look closely with a torch, you may find one; more often, flea dirt in the same spot is the sign that larvae are feeding there.

The flea life cycle, and how long fleas live

A flea goes from egg to larva to cocoon to adult, and at normal room temperature the whole cycle can take about eighteen days. Eggs hatch in two to five days, the larvae feed for eight to fifteen days and then spin cocoons, and the adults inside can wait for months, up to a year in cool conditions, until vibration or a rise in carbon dioxide tells them a host has arrived. On an animal, an adult cat flea lives for about thirty to forty days.

That waiting stage is the one that catches people out, and it explains why sprays and bombs miss the cocoon stage: a treatment on Saturday is followed by fresh fleas the week after, hatching from cocoons that were already there.

Can fleas live in your bed?

Fleas live on animals rather than in mattresses, but their eggs and flea dirt drop wherever an animal sleeps, so a bed or sofa that a pet uses can end up with larvae in the bedding and around the base. The signs are black specks on the sheets, usually at the foot of the bed where the cat curls up, and bites on the legs soon after lying down.

If there is no animal in the house and the bites are on the upper body after a night's sleep, the bed itself needs checking for another culprit, and it is worth learning how to check a bed for bed bugs before treating for fleas.

Where fleas come from when there is no pet

There are three usual sources. Fleas left behind by a previous occupant's animal can wait as cocoons for months and hatch the week you move in. An animal using the space under the house, such as a stray cat or rats, can keep fleas breeding in the subfloor. Or a neighbour's cat may be sleeping on your deck or under the floor. Rentals between tenants and houses left empty over summer are the classic cases.

Check the subfloor vents and the ground under any deck for signs of an animal: flattened bedding, fur, droppings or a smell. If one has been living there, the subfloor needs treating as well as the carpet, or the fleas will keep coming up.

What the signs tell you to do next

Where you found the most flea dirt and the most bites is where the eggs and larvae are concentrated, and that is where treatment has to go first: the pet's bed and the floor around it, the sofa it sleeps on, the hallway it walks along. A whole house rarely needs the same attention in every room.

If the signs are confined to one or two rooms and you have caught them early, you can deal with it yourself with a step by step plan to clear them, starting with the pet and the vacuum cleaner. If they are everywhere, or under the house, that is the point to have it treated.

Questions

Questions about flea signs

Can you see flea eggs with the naked eye?

Only just. At about half a millimetre long they look like tiny white specks, a little like grains of salt, but on carpet or bedding they are nearly invisible because they fall deep among the fibres. Flea dirt, which is black and ends up in the same places, is much easier to find and tells you the same thing.

Is it flea dirt or just dirt?

Use the damp paper test. Put the black specks on wet white paper or a damp paper towel and wait a moment. Flea dirt is digested blood, so it dissolves into reddish brown smears. Soil, dust and fluff stay grey or brown. Flea dirt is also often described as looking like ground pepper or black dandruff in the pet's coat.

How quickly do fleas spread through a house?

Quickly, once breeding starts. A single female lays twenty to fifty eggs a day, and in a warm house the cycle from egg to biting adult can turn over in under three weeks. A handful of fleas brought in by a pet can become a noticeable problem within a month or two, which is why early signs are worth acting on.

Do fleas live on humans?

No. Cat and dog fleas bite people, mostly when they are hungry and no animal is around, and then drop off again, because people lack the fur they need to live and lay eggs in. There is a human flea, but it is rare in New Zealand. We have covered flea bites on people, including first aid, separately.

What actually kills flea eggs?

An insect growth regulator is the main thing, because it stops eggs and larvae developing into adults on the surfaces it reaches, though it does not kill adult fleas. Thorough vacuuming with a beater-type machine removes a good share of the eggs from carpet, and hot washing clears them out of bedding. Ordinary contact sprays aimed at adults are much less reliable against eggs.

Can fleas survive in an empty house?

Yes, as cocoons. Fully formed fleas can stay inside their cocoons for weeks, and for months in cool conditions, waiting for vibration or carbon dioxide to signal that someone has come home. That is why an empty rental or a house left over the holidays can greet the next people through the door with bites.

Sources

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