How can you distinguish fleas and lice on a cat?

Understanding the Importance of Identification

Why Accurate Identification Matters

Potential Health Risks for Cats

Fleas and lice on felines present distinct health hazards that require immediate attention. Both parasites can trigger dermatological reactions, but each carries additional systemic threats.

Flea bites often provoke allergic dermatitis, leading to intense pruritus, skin excoriation, and secondary bacterial infection. Heavy infestations may cause anemia, especially in kittens or debilitated cats. Fleas serve as vectors for Bartonella henselae (cat‑scratch disease) and transmit tapeworm eggs (e.g., Dipylidium caninum) when cats ingest infected fleas during grooming.
Lice infestations typically result in localized irritation, feather‑like scaling, and alopecia. Persistent scratching can breach the epidermal barrier, permitting opportunistic pathogens to invade. Although lice are not known to transmit zoonotic agents, severe infestations may precipitate anemia through chronic blood loss in vulnerable animals.

Combined infestations exacerbate immunological stress, increasing susceptibility to respiratory infections and delaying wound healing. Prompt identification and targeted treatment of each parasite mitigate these risks and protect overall feline health.

Effective Treatment Strategies

Effective treatment of parasitic infestations on felines requires precise identification of the culprit, followed by targeted interventions. Once fleas are confirmed, a multi‑modal approach yields the best results. Systemic oral products containing neonicotinoids or spinosads eliminate adult insects within 24 hours and disrupt the life cycle. Topical spot‑on formulations deliver insecticidal and insect growth‑regulating agents, providing rapid knock‑down and preventing egg maturation. Environmental control—vacuuming carpets, washing bedding at high temperatures, and applying insecticide sprays to indoor habitats—reduces reinfestation risk. Repeat applications according to label intervals maintain efficacy throughout the flea development window.

When lice are diagnosed, treatment protocols differ. Oral medications are ineffective; instead, apply a single dose of a veterinary‑approved insecticidal shampoo or a spot‑on solution containing pyrethrins or lufenuron. Ensure thorough grooming to distribute the product across the coat, targeting the head, neck, and tail base where lice concentrate. After treatment, isolate the cat for 24 hours to prevent transmission to other animals. Clean and disinfect grooming tools, bedding, and any surfaces the cat contacts; washing with hot water or using a dilute bleach solution eliminates residual nits.

Both parasite types benefit from regular preventive schedules. Administer monthly flea preventatives to all indoor and outdoor cats, and schedule routine examinations to detect early lice infestations. Combining pharmacologic measures with diligent environmental hygiene minimizes recurrence and safeguards the animal’s health.

Key Differences Between Fleas and Lice

Physical Characteristics

Size and Shape

Fleas are noticeably larger than cat lice. An adult flea measures 1.5–3 mm in length, while a cat louse rarely exceeds 1 mm. The flea’s body is laterally compressed, giving it a flattened appearance from side to side, which facilitates movement through fur. Lice are dorsoventrally flattened, presenting a thin, leaf‑like profile that adheres closely to the hair shaft.

The shape of the head also differs. Fleas possess a small, rounded head that does not protrude beyond the thorax; their mouthparts are adapted for piercing skin and sucking blood. Lice have a broader head with visible antennae and chewing mouthparts that remain visible when the insect is examined under magnification.

These dimensional and morphological traits allow rapid visual discrimination during a physical examination of a cat’s coat.

Coloration

Coloration provides a reliable visual cue when separating flea infestations from lice colonies on felines. Fleas are typically dark brown to black, with a slightly flattened, oval body that reflects light, giving a glossy appearance. Their legs are long relative to body size, and the abdomen may appear mottled after a blood meal. In contrast, cat lice are pale to light gray or off‑white, with a softer, more matte texture. Their bodies are broader and flatter, and the legs are short, making the insects appear more compact.

Key coloration differences:

Flea: dark, glossy, often with a reddish hue after feeding.
Lice: pale, matte, lacking any sheen.
Movement visibility: fleas may be seen jumping, creating brief flashes of dark color; lice crawl slowly, remaining within the light‑colored range.

Observing these color patterns on the cat’s coat, especially in areas where parasites concentrate (neck, base of the tail, and behind the ears), enables precise identification without additional testing.

Movement Patterns

When inspecting a cat, the way ectoparasites move can be a decisive factor in identification.

Fleas exhibit rapid, erratic locomotion. They jump several centimeters when disturbed, traverse the host’s coat in short bursts, and frequently appear on the lower abdomen, base of the tail, and hind legs. Their movement is visible as quick, darting hops that cease when the animal is brushed or when a flea comb is applied.

Lice display slow, deliberate crawling. They remain on the surface of the fur, moving only a few millimeters at a time. Their activity is concentrated around the head, neck, and forelimbs, where they feed continuously without jumping. Lice are rarely seen moving when the cat is handled; they are noticed primarily by the presence of a fine, moving line of insects.

Key movement distinctions

Jumping ability: fleas – yes; lice – no.
Speed: fleas – high; lice – low.
Typical locations: fleas – lower body and tail; lice – head, neck, forelimbs.
Visibility during handling: fleas – easily observed moving; lice – often immobile until disturbed.

Observing these patterns allows a rapid, reliable separation of the two parasite types without reliance on microscopic examination.

Life Cycle Stages

Flea Life Cycle

Understanding the flea life cycle is essential when trying to differentiate flea infestations from lice on a cat. Fleas develop through four distinct stages, each with characteristic behavior and appearance that do not occur in lice.

Egg: Tiny, white, and smooth; deposited on the cat’s fur or in the environment, often falling off during grooming.
Larva: Blind, worm‑like, and active in the litter or carpet; feeds on organic debris, not on the host’s skin.
Pupa: Enclosed in a silken cocoon; remains hidden in carpets, bedding, or cracks until stimulated by vibration or heat.
Adult: Hardened, laterally flattened, and capable of jumping; attaches to the cat’s skin, feeds on blood, and causes visible, irregular bite marks.

Lice, by contrast, complete their entire life cycle on the host, lack a pupal stage, and cannot jump. Recognizing the presence of eggs, larvae, or cocoons in the environment points to fleas, while only adult insects found directly on the cat suggest lice. This distinction guides appropriate treatment and environmental control measures.

Louse Life Cycle

Understanding the life cycle of cat lice is essential for recognizing their presence and separating them from flea infestations.

Adult lice are wingless insects that remain permanently on the host. They feed on skin debris and blood, causing irritation that differs from the rapid, jumping movement typical of fleas. Female lice lay eggs—commonly called nits—directly on the hair shaft close to the skin. Nits are oval, white, and firmly attached, making them difficult to dislodge without combing.

The developmental sequence proceeds as follows:

Egg (nit) – incubation lasts 5–10 days at normal indoor temperatures; the egg hatches in situ.
Nymph – three successive molts occur over 10–14 days, each stage resembling a miniature adult but lacking full reproductive capacity.
Adult – after the final molt, the insect reaches reproductive maturity and begins laying eggs, completing a cycle of approximately 2–3 weeks.

Key diagnostic features derived from the life cycle include:

Location: Lice concentrate on the head, neck, and forelimbs, where hair is dense; fleas favor the base of the tail, abdomen, and between the toes.
Mobility: Lice crawl slowly and do not jump; fleas exhibit rapid, erratic jumps when disturbed.
Egg attachment: Nits remain glued to hair; flea eggs are loosely deposited in the environment and fall off the host.

Recognizing these biological markers enables accurate differentiation between the two parasites, allowing targeted treatment and prevention strategies.

Preferred Locations on the Cat

Flea Habitats

Fleas thrive in environments where they can access a host and remain hidden between feedings. Typical flea habitats include:

Carpets and rugs, especially in high‑traffic areas.
Pet bedding, blankets, and cushions that retain moisture.
Upholstered furniture with fabric folds and seams.
Outdoor spaces with tall grass, leaf litter, or soil where adult fleas emerge.
Cracks and crevices in flooring or walls that retain debris.

These locations provide darkness, humidity, and a supply of organic matter, allowing flea larvae to develop safely. Adult fleas leave these habitats only to locate a warm‑blooded host, where they attach to the skin and feed.

In contrast, lice complete their entire life cycle on the cat’s body, preferring the fur and skin of the head, neck, or tail. Recognizing that fleas originate from external environments while lice remain confined to the animal itself helps differentiate the two infestations.

Louse Habitats

Distinguishing fleas from lice on a cat relies on recognizing the specific environment each parasite occupies. Lice remain permanently on the host, inhabiting regions where they can grasp hair shafts and feed on skin debris. Typical louse locations include:

The head, especially around the ears and whisker pads, where hair is dense and close to the skin.
The neck and shoulder area, where the coat forms a tight, short‑to‑medium length layer.
The ventral abdomen and groin, where skin folds provide shelter.
The base of the tail, where the fur is thin and the skin is exposed.

Lice embed their legs in the hair shaft, move only by crawling, and are rarely found in the surrounding environment. Their presence is confined to the cat’s body, with no off‑host stages. Observing parasites clustered in the described zones, attached to individual hairs, strongly indicates a louse infestation rather than flea activity, which typically occurs on the lower back, near the base of the tail, and involves jumping off the host to develop in the environment.

Evidence of Infestation

Flea Dirt «Faeces»

Flea dirt, the digested blood excreted by adult fleas, appears as tiny, dark specks on a cat’s coat. The particles are roughly the size of sand grains and turn reddish when moistened, confirming the presence of blood. This sign is typically found in areas where fleas congregate—base of the tail, abdomen, and neck folds.

Lice, by contrast, lay transparent, oval eggs (nits) firmly attached to hair shafts. Nits do not change color when wet and are usually positioned close to the skin on the head, ears, and forelimbs. The absence of flea‑type specks in these regions helps separate a lice infestation from a flea problem.

Key characteristics of flea dirt

Dark, sand‑like appearance
Reddish tint after adding water or saline solution
Concentrated on the lower back, tail base, and neck
Easily removable with a fine‑tooth comb or tape test

Key characteristics of lice eggs

Transparent, oval shape
Firmly glued to hair shafts, often near the skin surface
Located on the head, ears, and forelimbs
No color change when wetted

Identifying flea dirt accurately enables rapid distinction between flea and lice infestations, allowing targeted treatment for the cat.

Nits «Louse Eggs»

Nits are the eggs of chewing lice and appear as tiny, oval, whitish to yellowish shells attached firmly to individual hairs. Each nit measures about 0.5 mm in length and has a characteristic operculum (a small cap) at one end. The shell is translucent, allowing the developing embryo to be seen as a faint dark spot inside.

Lice lay nits close to the skin, typically on the base of the hair shaft near the head, neck, and behind the ears. The attachment is permanent; nits do not detach easily and remain visible until they hatch or are manually removed.

Key differences from flea evidence:

Position: nits are fixed at the hair root; flea eggs are laid loosely on the fur and fall off readily.
Mobility: nits stay in place; flea feces (often called “flea dirt”) appear as small, dark specks that can be brushed away.
Shape: nits are oval with a visible cap; flea eggs are smooth, elongated, and lack an operculum.
Reaction to pressure: pressing a nit with a fingernail will not crush it, whereas flea dirt smears and turns reddish when moistened.

To confirm the presence of nits, isolate a single hair and examine it under magnification. The operculum should be visible, and the shell will be firmly anchored to the shaft. Removal requires a fine-tooth comb or specialized nit‑removal tool, followed by thorough grooming to prevent reinfestation.

Skin Irritations and Lesions

Skin irritations caused by fleas typically appear as small, raised papules surrounded by redness. The lesions often cluster around the base of the tail, dorsal neck, and lower back, where fleas feed. Scratching may produce tiny puncture marks and a gritty feeling as flea feces (dark specks) accumulate in the fur.

Lice infestations generate a different pattern. Lesions are usually confined to the head, ears, and forelimbs, where lice cling to hair shafts. The skin may show uniform redness, thinning hair, and a fine, silvery‑gray crust that results from lice saliva and debris. Lice do not leave visible droppings, but a light dusting of nits can be seen attached to the hair shafts.

Key visual differences:

Location: fleas → tail base, back; lice → head, ears, forelimbs.
Lesion type: fleas → punctate papules with dark specks; lice → smooth redness with nits.
Hair condition: fleas → normal hair length; lice → hair thinning and nits.
Presence of debris: fleas → dark fecal spots; lice → no fecal stains, only nits.

A quick examination focusing on these criteria allows precise identification of the parasite responsible for the cat’s skin irritation. Prompt treatment can then target the specific ectoparasite, reducing discomfort and preventing secondary infection.

How to Conduct an Examination

Tools for Inspection

Fine-toothed Comb

A fine‑toothed comb is a practical tool for separating and identifying ectoparasites on a cat. Its tightly spaced teeth trap both flea bodies and lice nits, allowing visual confirmation without magnification.

When the comb is drawn through the coat, observe the material collected on the teeth:

Flea fragments appear as dark, irregularly shaped insects, often moving quickly when disturbed.
Lice nits cling to the teeth as oval, white or translucent shells attached to hair shafts; they remain stationary.
Live lice may be seen as small, tan or gray insects crawling along the comb.

The comb also reveals infestation intensity. A few fleas suggest a temporary exposure, while numerous nits indicate a breeding population of lice that requires targeted treatment.

Effective use involves:

Wetting the cat’s fur slightly to reduce static.
Starting at the base of the hair near the skin and pulling the comb toward the tip in short strokes.
Inspecting each tooth after every pass, using a magnifying glass if needed.
Disposing of captured parasites in a sealed container for accurate identification.

Regular combing, performed weekly, provides early detection of either parasite and guides appropriate veterinary intervention.

Magnifying Glass

A magnifying glass provides the resolution needed to examine ectoparasites on a cat’s coat without invasive procedures. By holding the lens a few centimeters from the fur, the observer can discern size, body shape, and behavior that separate flea infestations from lice colonization.

Flea characteristics observable under magnification
• Size: 1–3 mm, rounded, laterally compressed.
• Color: dark brown to reddish.
• Movement: rapid, intermittent jumps when disturbed.
• Location: predominantly on the lower back, base of the tail, and between the hind legs.
Lice characteristics observable under magnification
• Size: 2–4 mm, elongated, dorsoventrally flattened.
• Color: pale gray or tan.
• Movement: slow, crawling along hair shafts; no jumping.
• Location: primarily on the head, neck, ears, and forelimb hair.

The magnifying glass also reveals attachment points. Fleas are often seen on the skin surface, occasionally near blood spots from feeding, while lice are attached to the hair shaft with their claws. Identifying these differences allows accurate diagnosis and targeted treatment.

White Paper or Cloth

A white sheet or light-colored cloth provides a contrasting background that makes the size, shape, and movement of ectoparasites on a cat readily visible. When the animal is gently restrained, run the fabric over the coat, especially along the neck, back, and tail base. The contrast highlights individual organisms, allowing rapid visual differentiation.

Fleas: dark brown, laterally flattened, 1–4 mm long, jump when disturbed, often seen moving quickly across the fabric. Their bodies exhibit a hard exoskeleton and a visible head‑thorax‑abdomen segmentation.
Lice: pale to light gray, elongated, 1–2 mm long, crawl rather than jump, remain attached to hair shafts. Their legs are visibly longer relative to body size, and the abdomen appears softer.

Examine the collected material under a magnifying lens or handheld microscope. Fleas will show a hardened, compact form with strong hind legs adapted for jumping. Lice will display a more delicate body, longer legs, and a tendency to cling to hair bases. Record the observed traits; the presence of jumping insects confirms fleas, while crawling, hair‑bound insects confirms lice. This method yields a quick, reliable assessment without chemical agents.

Step-by-Step Inspection Process

Visual Examination

A visual examination is the primary method for separating flea infestations from lice colonies on a cat. The observer must focus on size, shape, movement, and location of the parasites.

Fleas are 1–3 mm long, laterally compressed, and dark brown to reddish. They jump when disturbed, often appearing on the base of the tail, the neck, and the back of the legs. A cat may show rapid scratching or a “flea dirt” residue (tiny black specks) near the skin.
Lice measure 2–4 mm, are more elongated, and range from gray to tan. They crawl rather than jump and remain attached to the hair shaft. Typical sites include the head, ears, and forelimbs. Lice infestations produce a dry, scaly crust and may cause localized hair loss.
Live fleas are usually seen moving quickly across the fur, while lice move slowly, often staying close to the scalp or ear margins.
Inspection under a bright light or with a magnifying lens improves detection of the tiny insects and their eggs.
Removing a single specimen for microscopic confirmation provides definitive identification.

By systematically scanning these regions and noting the described characteristics, a caregiver can accurately differentiate between flea and lice presence without laboratory testing.

Combing Technique

Combing provides a rapid, non‑invasive way to tell whether a cat is infested with fleas or lice. A fine‑toothed flea comb (spacing 0.5 mm) extracts adult fleas, eggs and larvae, while a wider, metal lice comb (spacing 1–2 mm) lifts the smaller, crab‑shaped lice and their nits.

The procedure begins with a calm cat, preferably after a short grooming session. Hold the comb at the base of the fur, pull a small section taut, and draw the comb through the hair toward the tip. Repeat every few centimeters along the back, neck, tail base and underbelly. After each pass, wipe the teeth on a white tissue or tray to examine captured material.

Key visual distinctions observed during combing:

Flea fragments: dark, oval bodies about 2–4 mm long; movement when disturbed; occasional blood spots from flea feces.
Flea eggs: white, oval, 0.5 mm, often clustered near the base of the comb.
Lice: pale, flat, crab‑like insects 1–2 mm long; no jumping ability; often seen attached to hair shafts.
Lice nits: cemented, oval shells firmly attached to the hair shaft, usually near the scalp or along the neck.

If the comb yields predominantly moving, larger insects and noticeable blood specks, fleas are the likely culprit. If the comb shows small, immobile, crab‑shaped creatures and firmly attached nits, lice are present. Consistent combing over several days confirms the diagnosis and guides appropriate treatment.

Interpreting Findings

When examining a cat for ectoparasites, the first step is to translate visual and tactile observations into a reliable diagnosis. Accurate interpretation of findings prevents misdirected treatment and reduces the risk of resistance.

The most decisive indicators are:

Location on the host – Fleas congregate near the neck, base of the tail, and between the shoulder blades, where blood meals are easiest. Lice remain on the skin surface, preferring the head, ears, and forelimbs, often avoiding the dense fur of the back.
Size and morphology – Fleas measure 2–4 mm, possess a laterally flattened body, and exhibit strong jumping legs. Lice are 1–3 mm, have a more rounded, dorsoventrally flattened shape, and lack jumping ability.
Movement pattern – Fleas jump when disturbed; lice crawl slowly and may be seen dragging their hind legs.
Excrement characteristics – Flea droppings appear as black, granular specks resembling pepper; lice feces are fine, pale, and often mixed with skin debris.
Skin reaction – Flea bites cause punctate erythema and small crusts, typically in clusters. Lice feeding leads to diffuse scaling, hair loss, and a “sandpaper” feel when the coat is stroked.

After gathering these data, compare them against established criteria. If the majority of signs align with flea characteristics, initiate an adulticide and environmental control protocol. If lice features predominate, select a pediculicide formulated for felines and focus treatment on the affected regions. In mixed infestations, apply both agents sequentially, ensuring that each product’s safety profile permits concurrent use.

Interpretation must also consider secondary factors: recent travel, contact with other animals, and the cat’s grooming behavior. These contextual clues refine the diagnosis and guide a targeted, evidence‑based intervention.

When to Seek Veterinary Advice

Signs of Severe Infestation

Extensive Hair Loss

Extensive hair loss in cats often signals an underlying parasite problem, and the pattern of shedding helps separate flea infestations from lice. Flea‑induced alopecia typically appears as irregular, patchy thinning, frequently centered around the base of the tail, hindquarters, and abdomen. The skin in these zones may be reddened, inflamed, or contain small bite marks. Lice, by contrast, cause more uniform thinning along the neck, head, and forelimbs, where the insects cling to hair shafts. The affected area usually remains smooth, without the punctate lesions characteristic of flea bites.

Key diagnostic clues include:

Presence of flea feces (dark specks) on the fur or bedding; lice leave no such debris.
Microscopic examination: fleas are larger, jump‑capable insects; lice are smaller, wingless, and move slowly across the hair.
Grooming behavior: cats with fleas often scratch vigorously and bite at the skin; lice‑infested cats display excessive licking rather than scratching.

Treatment strategies differ. Flea control relies on adulticide sprays, spot‑on products, and environmental decontamination to break the life cycle. Lice eradication requires a pediculicide shampoo or spray applied directly to the coat, followed by a repeat dose after the lice mature. Monitoring hair regrowth over two weeks confirms successful parasite removal; persistent alopecia suggests secondary infection or allergic dermatitis, warranting veterinary assessment.

Open Sores or Infections

Open sores or secondary infections frequently reveal which ectoparasite is present on a cat. Flea bites produce small, red papules that quickly develop into puncture wounds; scratching often leads to crusted lesions that may ooze pus. Lice feed continuously along the hair shaft, causing linear abrasions that rarely break the skin. When the skin is breached, bacterial invasion is common with flea infestations because the bite sites are deeper and more inflamed. Lice‑related irritation typically results in mild erythema without true ulceration.

Key observations for differentiating the two based on wound characteristics:

Location – Flea‑induced sores appear on the lower abdomen, base of the tail, and inner thighs; lice‑related abrasions are found on the head, neck, and forelimbs where the insects concentrate.
Shape and size – Flea wounds are round, 1–3 mm in diameter, often surrounded by a halo of redness; lice lesions are thin, elongated scratches following the hair line.
Exudate – Flea lesions may produce clear or purulent discharge; lice lesions rarely exude fluid.
Secondary infection – Bacterial infection, characterized by swelling, heat, and foul odor, is more prevalent with flea bites due to deeper tissue damage.

Monitoring these parameters enables rapid identification of the offending parasite and guides appropriate treatment. Prompt veterinary intervention reduces the risk of systemic infection and accelerates recovery.

Behavioral Changes

Behavioral observations provide reliable clues when identifying whether a cat is infested with fleas or lice.

Flea‑related changes
- Frequent scratching, especially along the spine, tail base, and hindquarters.
- Rapid, short bursts of grooming that target the lower back and tail.
- Restlessness and frequent shifting of position while seated.
- Sudden aversion to lying on soft surfaces that may expose the skin.
Lice‑related changes
- Persistent head‑to‑neck rubbing with the forelimbs or against furniture.
- Continuous licking of the ears and facial region.
- Localized agitation around the head, ears, and neck, often accompanied by head shaking.
- Reduced grooming of the rest of the body, focusing effort on the affected area.

Both parasites may cause general irritability, but the location and pattern of the cat’s response differ. Fleas provoke widespread, quick scratching, while lice produce concentrated head and neck irritation. Recognizing these distinct behavioral patterns enables accurate identification and timely treatment.

Confirmation and Treatment Options

Professional Diagnosis

Professional diagnosis of ectoparasite infestations in felines requires systematic evaluation by a trained veterinarian. The practitioner begins with a thorough physical examination, focusing on predilection sites for fleas (neck, base of tail, abdomen) and lice (head, neck, ears, ventral surface). Visual inspection under adequate lighting reveals characteristic morphology: fleas are larger, laterally compressed, and exhibit rapid jumping behavior; lice are smaller, elongated, and remain attached to hair shafts.

Microscopic analysis confirms identification. Samples collected with fine-toothed combs or adhesive tape are placed on slides and examined for distinctive anatomical features: flea adults possess hardened exoskeletons and prominent hind legs, whereas lice show segmented bodies with clawed legs adapted for clinging.

Laboratory testing may include:

Dermal scrapings for microscopic evaluation.
PCR assays targeting species‑specific DNA when infestation is ambiguous.
Fecal flotation to detect flea eggs or larvae in the environment.

Differential diagnosis considers other skin conditions (dermatophytosis, allergic dermatitis). Treatment plans are formulated based on confirmed parasite type, severity of infestation, and the cat’s health status. Prescription of appropriate ectoparasiticides, environmental decontamination, and follow‑up examinations ensure effective eradication and prevent reinfestation.

Prescription Medications

Prescription medications are the primary tool for confirming whether a cat is suffering from flea or lice infestation. Flea‑specific products contain active ingredients that target flea biology, while lice‑targeted drugs incorporate compounds that affect lice physiology. Selecting the correct drug therefore reveals the parasite type, because each medication is approved for a single class of ectoparasite.

Flea‑oriented prescriptions include:

Spinosad (e.g., Comfortis) – oral, rapid kill of adult fleas, no activity against lice.
Selamectin (e.g., Revolution) – topical, effective against fleas and certain mites but not lice; dosage differs when used for flea control.
Nitenpyram (e.g., Capstar) – oral, fast‑acting adult flea kill; ineffective on lice.
Lotilaner (e.g., Credelio) – oral, flea‑only label, no lice indication.

Lice‑oriented prescriptions include:

Ivermectin (injectable or oral formulations) – systemic, approved for feline lice, does not eradicate fleas at standard doses.
Moxidectin (e.g., Advocate) – topical, labeled for lice treatment, lacks flea‑specific efficacy.
Selamectin, when applied at the higher dosage recommended for lice, distinguishes lice infestations from flea problems because the flea label requires a lower concentration.

The distinction hinges on the approved indication and dosing schedule. When a veterinarian prescribes a flea‑only medication, the presence of fleas is assumed; conversely, a lice‑specific prescription confirms lice involvement. Accurate identification of the parasite guides therapeutic choice and prevents unnecessary exposure to ineffective agents.