A new identification guide to British beetle larvae

Over 40 years in development, the RES Handbook to British Coleoptera larva was published on 1 August 2019. You can order the book online from the FSC website.

For the first time, the Handbook will provide full guidance on taking the identification of beetle larvae to at least family level. At the same time, by keying to genus where possible and including extensive references to other published works, the Handbook will guide the user to more precise identifications.

Why was a new guide needed?

The order Coleoptera is one of the largest groups of animals, with around 400,000 species currently described world-wide. Although relatively poor in species (4072 according to Andrew Duff's 2012 checklist), the British beetle fauna is reasonably diverse at family level. 103 of approximately 176 world families are represented in Great Britain.

Like butterflies and moths, beetles undergo complete metamorphosis, with four distinct life-stages: egg, larva, pupa and adult.

Most beetles spend the majority of their lives as larvae. The longest recorded larval development, more than 50 years, is for a North American wood-feeding buprestid with an adult life of just a few weeks.

Arguably it's at this larval stage where beetles make their greatest ecological impact, since larvae are primarily occupied with feeding.

Despite the importance of the three immature life-stages, most identification guides only cover the adults. For more than 100 genera in Britain, especially in the families Staphylinidae, Leiodidae and Histeridae, the larvae stages are still effectively unknown. The only way to identify many specimens has been to rear the larvae to adults.

Finding beetle larvae

Many biological recorders will have caught beetle larvae, perhaps in pitfall traps, through leaf litter sieving and in kick-samples of freshwater gravels, or in decaying wood, flowers and seed cases, or even in galls and mines.

In a number of taxa, larvae are much more likely to be encountered than the adults, especially when the adults are short-lived and seasonal. For example, the distinctive velvety larvae of the Cantharidae (soldier beetles) may be found throughout the year, sometimes in numbers in leaf litter or pitfall traps, while the adults only appear for a restricted time during the warm months.

Some adults are elusive and unlikely to be casually collected. A good example is the click beetle Stenagostus rhombeus, not uncommonly found as larvae in tree stumps and decaying logs in wooded parts of southern England, but with its nocturnally active adults rarely seen. Guidance on specimen preparation is included in the Handbook.

Identifying beetle larvae

First of all, how can you be sure that your specimen is actually a beetle larva? To help answer this critical question, the Handbook features a detailed preliminary key, with 33 couplets, to distinguish Coleoptera larvae from other immature insects.

This leads to the main key, with 163 couplets, to the 103 families and many of the subfamilies. To keep the key simple, several of the larger families key out in more than one place. The second half of the Handbook is a systematic survey of the biology of each family.

The RES Handbook to British Coleoptera larva is due for publication on 1 August 2019. You can order the book online for a special pre-publication discounted price at FSC website.