Elateridae of the British Isles

Lifecycle

As with many insects, the Elateridae undergo a complete metamorphosis in order to complete their lifecycles.

Complete metamorphosis -

Ovum (egg) – Larvae – Pupa – Imago (adult)

Generally eggs are laid just below the soil surface or within suitable trees in May, June and July, when the insects are adult. The larvae are often referred to as ‘wireworms’ due to their long thin appearence and tough outer cuticle. The larvae of two species, Lacon querceus and Agrypnus murinus are more grub-like with a fleshy appearence and Cardiophorus spp. and Dicronychus equisetioides larvae are very long, without true segmentation.

Soil dwelling species will feed on rotten vegetation and the roots of numerous plants including brassicas, beans and cereals, as well as other invertebrate larvae and imagos.  In some areas of the world wireworms can be potentially serious crop pests. Saproxylic species rely on dead, decaying wood and whilst most are predatory they will also feed on rotting wood. Cannibalism has been known within Elateridae larvae.  

Depending on species larvae can grow up to around 40mm in length and change in colour from white/off-white in their early instars to a range of colours from cream or yellow to dark brown in the later instars, often with a noticeably darker head. They have three pairs of small legs on the segments just behind the head.

Elateridae larvae can go through several instars, in some species this figure can be into double figures and the larval stage can last up to 3-4 years. During this time soil feeding larvae will feed from around 100-300mm below the soil surface depending on several factors including soil temperature and age of the larvae. Species feeding on rotten wood will be present in old tree trunks and roots. The time spent as larvae can vary due to temperature and food availability and suitability.

On reaching the end of the final instar, the larvae will pupate, either under the soil or under the bark of rotten wood. Some species will eclose in July or August, but then remain in their pupal cases until the following spring when they emerge. In other species, the imagos will emerge from their pupae and immediately leave the pupal case once the cuticle has hardened.

The imago click beetles will only live for a matter of weeks feeding on pollen. In this time they will mate and the females lay their eggs. The main emergence period for imago insects in Britain is May, June and into early July.