How to identify insects and invertebrates under logs and stones

A variety of insects and other invertebrates take refuge under logs and stones, safe from large predators, or damaging frosts in winter. Turn over a log briefly, or peep under the flaps of peeling bark, and you’ll reveal a menagerie.

Logs and stones provide a safe refuge in winter, where temperatures are fairly stable – only in very cold weather will ice form underneath logs. In their winter torpor, large ground beetles don’t feed; instead, they will snuggle up to slugs and earthworms without attacking.

Similarly, you’ll sometimes see mollusc-munching carrion beetles alongside snails and pearly slug’s eggs. If you’re lucky you’ll spot the buzzing snail-hunter, with a long, narrow snout adapted to probe the recesses of snail shells and extract the soft bodies.

To avoid their attentions, many snails will be sealed safely behind a door of hardened mucus. In a mild spell slugs may emerge to graze, but when frosts bite most take cover, along with millipedes and woodlice, snug in their deadwood dormitory.

All illustrations by Felicity Rose Cole

How to identify insects and invertebrates under logs and stones

Violet ground beetle (Carabus violaceus, above)

20–30mm. Large beetle with purple wingcase borders. Feeds on worms and other soft-bodied invertebrates.

Woodlouse spider (Dysdera crocata)

9–15mm long. Found most frequently in southern England. Its huge orange jaws pierce woodlouse armour.

Buzzing snail-hunter (Cychrus caraboides)

15–20mm. Long ‘snout’ probes snail shells. Also eats wide range of soft-bodied prey. Buzzes when handled.

Ground beetle (Abax parallelepipedus)

17–22mm. Black beetle with grooved wingcases. Eats earthworms and other soft-bodied invertebrates.

Carrion beetle (Silpha atrata)

10–15mm. Mat-black beetle with broad wingcases. Feeds on snails and a wide variety of carrion.

Devil’s coach-horse (Ocypus olens)

20–30mm. Black rove beetle with short wingcases. Raises tail when threatened. Eats slugs.

Common black millipede (Tachypodoiulus niger)

Up to 30mm. Coils when disturbed. Body has 30–60 segments. Feeds on decaying matter and fungi.

Flat-backed millipede (Polydesmus angustus)

Up to 25mm. Brownish, winged segments; appears flatter than black millipede. Often found under bark.

Common pill woodlouse (Armadillidium vulgare)

Up to 18mm. Found especially on limy soils. Similar pill millipede has more than seven pairs of legs.

Common striped woodlouse (Philoscia muscorum)

Up to 11mm. Fast-moving. Grey, brown or even orange, often with dark stripe.

Garlic snail (Oxychilus alliarius)

6–8mm. Translucent, shiny, pale-brown shell, dark grey body. Emits strong garlic smell when disturbed.

Great grey slug (Limax maximus)

Very large slug, up to 20cm. Body dark grey, with paler blotches and stripes – hence alternative name of leopard slug.