A life that is a lottery from start to finish!

Black Oil Beetles have the most extraordinary life cycle! 

I am lucky enough to have a good population of black oil beetles (Meloe proscarabaeus) in my garden – in fact most gardens in the village where I live, appear to have this fascinating beetle stomping around!

Oil beetles are so called due to the rather toxic, oily substance they release from their leg joints to deter predators. Having said that, I have now made them sound rather frightening – but don’t be scared – I regularly pick them up to move them to a safer place and I have never been “contaminated” by any substance!

The best thing about these big black beetles is their incredible life cycle, which quite honestly you couldn’t make up unless you have a particularly vivid imagination. It’s a very risky choice for a way to live, but if my local population is anything to go by – it works!!

The female digs a short burrow in the ground, in which she lays a vast number of bright yellow eggs – sometimes as many as 1,000 in the burrow, which she then back-fills. This huge number of eggs is important as the newly hatched larvae, which resemble a tiny louse and are known as 'triungulins', now have a monumental task ahead of them.

Having scrambled their way out of the burrow, they must then find a plant that is ideally in flower and climb all the way up to the flower head. There they must patiently wait until a bee lands on the flower to collect pollen and nectar. This is the chance that they have been waiting for, as they quickly climb aboard their winged host, hanging on with specially adapted feet that each have 3 hooks.

The problem is that they need to find specific hosts – mainly solitary bees species, if they are to successfully complete their life cycle. Unfortunately, many will jump onto the first insect that visits the flower head; choose a butterfly or bumble bee literally means that life is about to finish – what a lottery!

Luckily, enough beetle larvae seem to land up clinging to the correct bee host species, which then transport them back to their nest. The beetle larvae then disengage and immediately start to tuck into the bee’s pollen and nectar store and also any of the bee’s eggs that it can find.

Eventually the larvae, having gorged on its hosts hard gained produce, will pupate, hatching out as an adult beetle the following spring to start the whole process over again.

The mind boggles as to how in evolutionary terms this fascinating beetle landed up with such a programme of life!