Rugged Oil Beetle

The Rugged Oil Beetle (Meloe rugosus) is a native oil beetle in the UK. It is dull black in colour with a roughened body surface and straight antennae. It is very similar in appearance to the Mediterranean Oil Beetle (Meloe mediterraneus), but the Rugged Oil Beetle has a distinct narrow groove in the middle of its thorax. The Rugged Oil Beetle is also smaller than the Mediterranean Oil Beetle.

The Rugged Oil Beetle is most commonly found in flower-rich calcareous grassland on chalk and limestone, including chalk downs and vegetated coastal cliffs.

There are 5 species of oil beetle in the UK; 3 are rare in the UK (2 of these are listed as Vulnerable).  A further 3 species of oil beetle have become extinct in the UK – Meloe autumnalis, Meloe cicatricosis and Meloe variegatus.

• Size: Adults can be up to 19mm in length.  Beetle larvae are less than 0.5mm in length
• Life span: From egg to adult approximately 1 year
• Diet: Adult oil beetles feed on the leaves and petals of flowering plants and grasses; favourites include Dandelion (Taraxacum officinale) and Buttercups (Ranunculaceae). Larvae (known as triungulins) feed on stores in solitary bee nests, including the pollen and the bee egg and/or larvae.
• Reproduction: Oil beetles have one of the most extraordinary life cycles of any British insect – they are nest parasites of solitary mining bees. Females dig a short burrow into which they lay up to a thousand eggs. For Rugged Oil Beetles, these eggs develop and hatch between mid-April and July. Once they hatch the larvae (triungulins) climb to the top of the nearest flower and wait for a bee to arrive. They then grab onto the bee and hitch a lift back to its nest; the triungulin will then consume the pollen stores and either the egg or larvae of the bee. The triungulin will then stay in the bee’s nest, where it will pupate and emerge as an adult oil beetle when conditions are right the following autumn or winter.
• When to see: Adults can be found from September – April in calcareous grasslands in England and Wales. They are mainly nocturnal and are most active during mild, overcast evenings.  Triungulins can be found in mid-April – July.
• Population Trend:  Unknown but assumed to be declining – the Rugged Oil Beetle is classed as Nationally Scarce within the UK.
• Threats: Oil beetles are reliant on solitary bees to compete their life-cycles. The health of oil beetle populations is therefore dependent on the health and diversity of wild bees. The wildflower-rich habitats that oil beetles rely upon have declined in quantity and quality due to intensive management of the countryside. Oil beetles are sensitive to changes in land management and are a good indicator of the health of our countryside.
• Fun Fact: Female Rugged Oil Beetles can produce between 20000 and 30000 eggs during their lifetime!

How you can help: 

Buglife is working to increase awareness of invertebrates and the Rugged Oil Beetle through specific projects, such as Life on the Edge, Species on the Edge and campaigns, but we need your help!

Join a recording scheme and log your finds – send any records/sightings to the Oil Beetle Recording Scheme or download the iRecord app and get recording!

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