Photo by Ben Deed (CC BY 4.0)
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Pterostichus madidus, or the Black Clock Beetle, belongs to the Ground Beetle family (Carabidae). Most members of the family have lost the ability to fly because they are better hunters when on foot!
They're mainly meat-eaters, their favourites being slugs and snails. Nonetheless, these beetles are partial to all kinds of insects if available. They may have a cheeky nibble from garden fruits which lay low to the ground, too.
Find these shiny beetles hiding beneath stones, loose bark and grass tussocks in the daytime.
Traits

A garden resident that will help control pests, such as slugs, snails and caterpillars.

May graze on fruits that have fallen or touch the ground.
Appearance
Adults: Mature beetles can grow as large as 2cm but can be as small as 1.4cm. They're shiny black, with deep, vertical ridges visible on the elytra (wing casings). The pronotum is rounded and smooth, with a central indented line crossing the middle. In most cases the legs are red-brown, but this can vary in hue, and there are some forms with black legs.
Larvae: Information concerning beetle larvae is limited. They reside in borrows, feed upon small, soft-bodied insects, and undergo three moults before developing into the adult form. They're highly segmented and cream coloured, comprise three pairs of legs, and large mouthparts.
Symptoms
May graze on fallen fruits, or fruits that touch the ground.
Activity
Nocturnal
Personality
Order
Coleoptera
Family
Carabidae
Metamorphosis
Complete
Distribution
Native to Europe, these beetles are widespread across the UK.
Biological treatment
There's no need to remove these from the garden. They are present in low numbers and can provide pest control in the garden.