Sandflies and seaweed flies: why they bite some people more, and what works

Quick answer: how do you stop beach flies biting you?

Combine timing, cover and the right repellent. Avoid the worst times and places — biting midges and seaweed flies peak at dawn and dusk, in still air, and near damp sand or piles of rotting seaweed — so choose a breezy spot, away from the seaweed wrack line, in the middle of the day when they're less active. Cover exposed skin (light long sleeves, especially at dusk), and apply an effective repellent containing DEET or picaridin, which work far better than most 'natural' alternatives against midges. A breeze is your friend: these weak fliers struggle in wind, so a windward, open spot naturally keeps them off.

So the anti-fly formula is: breezy open spot away from seaweed, avoid still dawn/dusk, cover up, and use a DEET or picaridin repellent. That combination handles both sandflies and seaweed flies far better than any single measure.

What they actually are

Two different insects get blamed. 'Sandflies' on most beaches are actually biting midges (Culicoides and similar) — tiny flies, often barely visible ('no-see-ums'), whose females bite for blood and leave itchy welts; they breed in damp sand and mud near shore. (True sandflies proper are a different group in some regions.) Seaweed flies (kelp flies) are a separate nuisance: they breed in and swarm around piles of decaying seaweed on the strandline, and while most don't bite, some species do, and their sheer numbers are unpleasant. Both are strongly tied to damp, organic-rich beach environments.

So knowing the two helps: itchy welts with no visible insect point to biting midges; swarms over seaweed piles point to seaweed flies. Both are avoided by similar means, but the seaweed-fly clue — beached weed — tells you exactly where the problem is.

• Beach 'sandflies' = tiny biting midges ('no-see-ums'), breeding in damp sand.
• Seaweed/kelp flies breed in rotting beach seaweed; some bite, all swarm.
• Both are tied to damp, organic, sheltered beach spots.

Why some people get bitten more

It's not your imagination — biting insects genuinely prefer some people. The females that bite are drawn by cues that vary between individuals: the carbon dioxide you exhale, body heat, and the specific mix of chemicals in your skin and sweat (which is partly genetic). Factors like being warmer, breathing harder (after activity), certain natural skin scents, and possibly some clothing colours can make you more attractive to them, while others nearby are relatively ignored. This is why two people on the same towel can have completely different experiences — the flies are choosing.

So if you're the one always bitten, you're likely genuinely more attractive to the insects by body chemistry, which you can't change much — but you can compensate with better cover, repellent and spot choice. The prevention works regardless of how appealing you are to them.

Repellents that work

For effective protection, the evidence favours repellents containing DEET or picaridin (icaridin), which reliably repel biting midges and flies and last for hours; DEET at moderate concentrations and picaridin are both well-established. Oil of lemon eucalyptus (PMD) is a plant-derived option with reasonable evidence, though generally shorter-lasting. Many other 'natural' repellents (citronella and similar) tend to be weaker and wear off quickly, offering limited protection against determined midges. Apply repellent to all exposed skin, reapply per the label (especially after swimming or sweating), and combine it with covering up at dawn and dusk for best results.

So choose a DEET or picaridin repellent for real midge protection, consider oil of lemon eucalyptus as a plant-based alternative, and don't rely on weak 'natural' sprays alone. Repellent plus cover-up plus spot choice is the winning combination.

Choosing your spot and time

Where and when you sit on the beach matters enormously. Biting midges and seaweed flies are weak fliers that hate wind, so an open, breezy spot — near the water's edge on the windward side, away from dunes, vegetation and the seaweed strandline — naturally keeps them off, while a sheltered nook behind dunes or beside beached seaweed concentrates them. Time-wise, they surge at dawn and dusk and in still, humid conditions, and quieten in bright, breezy midday. So a breezy, open, seaweed-free spot in the middle of the day is your best defence, and a still evening beside a pile of rotting weed is the worst case.

So use the landscape and clock: pick breeze and openness over shelter, keep away from beached seaweed, and favour midday over dawn and dusk. Spot and timing choice alone can be the difference between an untouched day and a bitten one.

Treating the bites

If you do get bitten, the priority is not to scratch, since scratching worsens the itch and can break the skin and cause infection. Soothe bites with over-the-counter antihistamines (oral or cream), hydrocortisone cream, calamine lotion, or a cold compress; the itch and small welts usually settle over a few days. Keep the area clean. Seek medical advice if bites become infected (spreading redness, warmth, pus), if you have a severe allergic reaction (widespread swelling, difficulty breathing — an emergency), or if you develop unusual symptoms after bites in regions where these insects transmit disease.

So bite treatment is standard soothing plus restraint from scratching, with the usual watch for infection or severe reaction. For most people, sandfly and seaweed-fly bites are an itchy nuisance that fades in days — the real win is preventing them with timing, cover and repellent in the first place.

A note: general information, not medical advice

This guide is general safety and wellbeing information for beachgoers, not medical advice. Reactions to stings, infections and heat vary between people, and severe or worsening symptoms — spreading pain, difficulty breathing, high fever, or signs of a serious allergic reaction — need urgent professional medical care.

If you are unsure, seek advice from a lifeguard, pharmacist or doctor, and call your local emergency number for anything severe. When in doubt, get it checked.