Why Dune Slacks Matter for Rare Insects

By Spotting Seals from Dune Lookout Points
Comments 35
1 Jul 2026

Why Dune Slacks Matter for Rare Insects

What Exactly Is a Dune Slack?

Walk along almost any British dune system and you will notice the pattern: a series of low sandy ridges running roughly parallel to the shore, like the ribs of a fan. Between those ridges lie hollows. Where the water table sits close enough to the surface, those hollows stay damp through most of the year, and that is a dune slack.

The name is old coastal dialect, and it describes the thing perfectly — a slack is a dip, a hollow, a place where the sand gives way to moisture. Because the water table in a dune system rises and falls with rainfall and tides, slacks are restless habitats. Some flood in winter and dry to cracked mud in August. Others stay permanently wet, holding shallow pools fringed with creeping willow and marsh orchids.

For insects, this instability is not a problem. It is the whole point.

Why Such a Small Habitat Punches Above Its Weight

Dune slacks are rare. They occupy a tiny fraction of the British coastline, and many have been drained, planted with conifers or lost to golf courses and caravan parks over the past century. What remains is fragmented, which makes every surviving slack valuable out of all proportion to its size.

What makes them special is the combination of conditions you rarely find together:

Bare, warm sand for burrowing and basking, right next to
Damp, cool ground that stays humid even in a heatwave, plus
Short, open vegetation maintained by grazing, wind and flooding, and
Fluctuating water levels that prevent any one plant from dominating.

Add low nutrient levels — dune sand is poor stuff — and you get a habitat where slow-growing specialists thrive and vigorous competitors struggle. That is precisely the recipe for rare invertebrates.

The Insects You Might Actually See

You do not need a permit or a microscope to enjoy this. A few species are genuinely approachable if you know where and when to look.

Dune tiger beetles are the headline act. Metallic green or bronze, fast as anything, they hunt across bare damp sand on sunny days from May to August. Watch for them running in short bursts, stopping, then darting again. They are visual hunters and will pause if you stand still.

Dune chafer beetles and various click beetles turn up in slacks with sparse turf, often under debris or in the roots of marram and creeping willow. Turning a single flat stone or a piece of driftwood in a slack can reveal half a dozen species in a minute.

Moths are the quiet treasures. The dune case-bearer and several scarce wainscots depend on slack plants such as creeping willow, bog pimpernel and the various sedges and rushes that colonise wet hollows. Many fly at dusk, so a slow walk along a slack edge in warm, still weather in July is far more productive than a midday march.

Amphibians deserve a mention too. Natterjack toads famously breed in shallow, warm, fish-free slack pools, and their rattling chorus on a May evening is one of the great sounds of the British coast. Great crested newts also use slack pools where the water stays in long enough for larvae to develop.

How to Walk a Slack Without Damaging It

Slacks are fragile in a very specific way. The vegetation is short and the soil is thin, so a few dozen pairs of boots in the wrong place can turn a botanically rich hollow into a muddy scar that takes years to recover. Practical rules that genuinely help:

Stay on the path where one exists. In dune systems, paths usually follow the drier ridges for a reason.
Walk on bare sand, not on vegetation, if you must cross a slack. Sand recovers; a crushed patch of moss and willow does not.
Avoid wet slacks after heavy rain and in winter. You will sink, and you will leave permanent footprints in the peat.
Keep dogs on a short lead around slack pools between March and August. Natterjack tadpoles and newt larvae are easily disturbed.
Never lift stones and leave them unturned, and never collect. Put anything you move back exactly as you found it.
Binoculars beat close approach every time for beetles and basking insects.

Wear shoes you do not mind getting damp. The best slacks are the ones where you feel slightly unsure of your footing.

Where and When to Go

Good dune slack habitat survives around the British coast in places such as the Sefton coast in Merseyside, the Ynyslas and Kenfig systems in Wales, the machair fringes of the Scottish islands, and the dune networks of North Norfolk and Lincolnshire. Local wildlife trusts run guided walks in several of these, and a guided walk is by far the quickest way to learn which hollows hold what.

Timing matters more than location. Late May and June give you breeding amphibians, emerging beetles and long, mild evenings. July and August are best for day-flying insects and moths at dusk. September brings a second wave of activity before the slacks refill with autumn rain.

Go quietly, go slowly, and look down more than you look out. The rarest inhabitants of a dune slack are usually within two metres of your feet.

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5 Comments

Robert Sonny says Jul 21, 2024 at 10:00am

I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system
Reply
- John Abraham says Jul 21, 2024 at 10:00am
  
  I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system
  Reply
  - Robert Sonnysays Jul 21, 2024 at 10:00am
    
    I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system
    Reply
Robert Sonny says Jul 21, 2024 at 10:00am

I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system
Reply

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