Wildlife Wednesday – Oil beetle

A few days ago my son came across this extraordinary beast in the garden. Measuring about 30mm long this is a pretty big beetle. None of us have ever seen one before. So first it was run for the camera, and then run for the identification books.

While we were looking through the books, my son suggested it may be an oil beetle. We’d never seen one of these but the evening before we had been reading about them in My Family and Other Animals by British naturalist Gerald Durrell (a book I had read many years ago and was just rereading with the children). And funnily enough that is exactly what it was!

After a search on the internet we could find very little about this beetle in Ireland though my insect book suggested it was found throughout the island. There were no records on the national biodiversity database (Update: I was incorrect – there are three records, one each for counties Clare, Cork and Wexford) but there were articles about it occurring on the island. A search on UK websites brought more information. In fact Buglife UK started a citizen science oil beetle hunt last year. From UK’s National Biodiversity Network (NBN) we found that the five British native oil beetles species have suffered drastic declines due to the changes in the way the countryside is managed and a further three oil beetle species are thought to be extinct.

The beetle has a fascinating life cycle. We spotted our beetle at 11am. By 2pm she had dug herself a hole in a bare soil bank. This is where she lays her eggs.

She can lay up to 1000 eggs, and they take 2-3 weeks to hatch. By 5.30pm our beetle was meticulously filling the hole in again. Once the eggs hatch, the louse like larva dig themselves out and climb up onto a flower. Once on the flower they wait for a passing solitary bee.

The larva climb onto the bee and hitch a ride back to the bees nest. Here they eat the bees eggs and turn into a grub like life stage. They then moult a few times before they pupate, still inside the bees nest, where they stay till they hatch into adults the following spring.

We think this one is the Black oil beetle – Meloe proscarabaeus, but are open to correction. (See comment below from thremnir who suggests it is in fact Meloe violaceus, the violet oil beetle)

25 thoughts on “Wildlife Wednesday – Oil beetle

  1. dust4y

    How fascinating, especially as you monitored the egg laying process throughout the day. Your son is clever to have spotted it and then to make an educated guess. Is there any chance their numbers could rise?

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    1. Murtagh's Meadow Post author

      Yes, his description of the scorpion incident at the dinner table had us rolling around the room in laughter the other day!

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  2. thremnir

    Meloe proscarabaeus was only recorded in Ireland for the first time in 2014 at Birr Co. Offaly. Since then, there have been around 25 more records (according to the Biodiversity Ireland portal); probably it has been here longer than that and been overlooked. There have been a similar no of records for M. violaceus, which was already long known here, in the same period. Both species crop up all over the southern half of our island. I have found both in. Co. Clare. They are not easy to tell apart. One key feature is supposedly the line of the back of the thorax, which is practically straight in M. proscarabaeus and noticeably incurved in M. violaceus. In practice its not always easy to see, but based on your last photo, it seems incurved, which if correct, would make your beetle M. violaceus.

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    1. Murtagh's Meadow Post author

      Thank you so much for that info. I have taken a video of it – would you be willing to have a look at that and see if you can confirm which of the two it was. I was using the buglife ID sheet to try and distinguish between the two.
      With thanks

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    1. Murtagh's Meadow Post author

      I imagine a lot of the larva die before they find a bee. As this is the first of these beetles I have seen, they are probably not plentiful. They are pretty big so pretty obvious – at least I hope so. I love my bees too.

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  3. afrenchgarden

    I first found these while weeding in the garden and sometimes I see them elsewhere. The ones I see are like yours, the violet oil beetle. They do look fascinating but I cannot help thinking about the poor bees. I have a hard time accepting parasites but they are all part of nature. Amelia

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  4. Pingback: Lens-Artists Challenge #171 – Weird and Wonderful | Murtagh's Meadow

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