Pot beetles are a fascinating group of petal and leaf-eating beetles that get their name from the protective shell-like ‘pot’ that the larvae live in, created using their own droppings! One of the key features of these beetles is that the head of the adults is hidden under their bulging pronotum (shoulder/thorax-covering), hence the scientific name for the genus Cryptocephalus, that means ‘hidden head’. Pot beetles belong to a large family of leaf beetles with 84 species in Europe and over 1500 species worldwide. There are currently 19 species of Cryptocephalus pot beetles in the UK, however many have suffered declines in their distribution and are now quite rare.
Latin name: Cryptocephalus sp.
Notable feature: The head of the adults is hidden under their bulging pronotum
Rarity in the UK: Rare / Common
Eight species of pot beetle are classified as Red Data Book species due to their scarcity, and 7 have been given Biological Action Plan (BAP) priority status. The BAP species include three that could easily be mistaken for ladybirds: the Six-spotted pot beetle (Cryptocephalus sexpunctatus), the Ten-spotted pot beetle (Cryptocephalus decemmaculatus) and the Rock-rose pot beetle (Cryptocephalus primarius).
The other BAP pot beetles include the beautiful Hazel pot beetle (Cryptocephalus coryli), the Shining pot beetle (Cryptocephalus nitidulus), the Pashford pot beetle (Cryptocephalus exiguus) and the Blue pepper-pot beetle, Cryptocephalus punctiger), which was one of the species named in the Guardian’s 2010 ‘Name a Species’ competition.
The most widespread species is Birch pot beetle (Cryptocephalus labiatus) which can be found throughout the British Isles in a variety of habitats, but most often in the foliage of broad-leaved trees, particularly birch.
After laying each of her eggs, the female pot beetle holds it in her back legs and spends time covering them with a waxy coating and some of her own droppings (know as frass) in a process known as ‘scatoshelling’. The process can take up to 10 minutes per egg, but it’s time well spent as the frass-covering has been shown to deter predators. If the female is disturbed while laying eggs she will abandon the egg without coating it, but these are far more likely to be eaten by ladybirds, lacewings and other predators than the coated eggs. Once she has coated the egg she lets it drop to the ground from the leaf or flower head that she is sitting on.
Once the larvae hatch they stay within their protective egg-case feeding on fallen leaves from their food plant. The larvae enlarge the neck of their pot as they grow using their own droppings. Beetle larvae lack the hardened wing cases of the adults, so the pot acts almost like a snail shell, providing protection and probably some camouflage. Despite this, it appears that predation of larvae is high, with ground beetles and small mammals such as wood mice taking many of the larvae. Pot beetle larvae tend to feed on leaf litter under the host plant, although they will sometimes eat fresh leaves later in their development. Larvae of some species can take up to 2 years to fully develop, where upon they seal up their larval cases and pupate, emerging as adult beetles a few weeks later.
The 4-spotted pot beetle (Clytra quadripuncta), is a closely-related species that also creates larval frass-pots, but interestingly, the larvae grow up inside ants nests. The female beetle drops her coated eggs near wood ants nests. The ants then collect the eggs, and carry them into the warm and protected nest where the larvae feed on plant debris within the nest.