Notable feature: Oil beetles are rather strange-looking beetles, their large abdomens protruding from under short elytra (wing cases) – they have been described as looking like some one whose waistcoat won’t button up!
Conservation Status: Not Evaluated
Where in the UK: Found throughout the UK, thought to be becoming less common in the north. Strongholds can be found in South West England and South Wales.
The Black Oil Beetle (Meloe proscarabaeus) is a native oil beetle in the UK. It is shiny black in colour, although some beetles may have a violet-blue sheen. It is very similar in appearance to the Violet Oil Beetle (Meloe violaceus), but has a straight base to the thorax and a very small rounded tooth at the base. Unlike the Violet Oil Beetle, there is also no depressed area at the base of the thorax.
Male beetles have strongly kinked antennae, whilst the females have slightly kinked antennae.
The Black Oil Beetle is most commonly found on wildflower-rich coastal cliff tops and lowland, unimproved grasslands. Occasionally it can be found on woodland sites.
The Black Oil Beetle is a priority species for conservation action in the UK Biodiversity Action Plan and identified as Nationally Scarce.
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: Adult beetles up to 30mm in length. Beetle larvae (triungulins) up to 1.5mm 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 Lesser Celandine (Ranunculus ficaria), soft grasses (Poaceae), 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. After leaving the nest, triungulins are often found on Lesser Celandine and Dandelion, but will use other flowers.
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 Black Oil Beetles, these eggs develop and hatch quickly, emerging later in the same season. Once these 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 next spring.
When to see: Adults can be found from March – June in meadows and coastal grasslands throughout Britain. They are most active on warm, sunny days. Triungulins can be found in May and June.
Population Trend: Unknown but thought to be declining. The Black Oil Beetle is a priority species for conservation action in the UK Biodiversity Action Plan and identified as Nationally Scarce.
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: In a female Black Oil Beetle’s lifetime, she may lay up to 40,000 eggs – this is over just a few months!
How you can help:
Buglife is working to increase awareness of invertebrates and the Black 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 appand get recording! Let us know what you find using #OilBeetleHunt on social media!
Do remember that we rely on donations to continue our work. If you have searched, found and learnt about our incredible invertebrates on our website, please do consider Making a Donation, Becoming a Memberor maybe even making a purchase in our shop. For more ideas on how to support our work find out how to Get Involved. Thank you 🕷
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