Oil Beetle

Image: Siga

Oh...

Turns out I don't like big butts at all!

Image: Chris Moody
Violet Oil Beetle (Meloe violaceus)

This most ungainly specimen is a species of Oil Beetle, a member of the genus Meloe. They belong to the Meloidae family, known as the Blister Beetles.

Despite their extraordinary waistline the "Oil" in question is not some awful cooking oil which turns your brain to mush and then puts it on your hips. Rather, it refers to the oily droplets of blood they release from their joints when disturbed. This is already queasy, but even worse is the fact that the stuff contains a poisonous chemical called cantharidin, which is potent enough to cause blistering in human skin.

Image: gailhampshire
Red-striped Oil Beetle (Berberomeloe majalis)

A lot of Blister Beetles are armed with this powerful toxin, hence the name. At least some are kind enough to advertise the fact with bright colours. In fact, they can actually look quite pretty with colours, patterns and iridescence all over a slim, dainty body.

Others are... different.

Image: José María Escolano
Meloe tuccius

We've already seen how some female Leaf Beetles experience an astonishing expansion of the waistline during the breeding season. It allows them to produce an incredible number of eggs, and the fact that it renders their wing cases somewhat useless and makes them look a bit disgusting is just something they'll have to bear.

Oil Beetles look like that all the time! Even the males! Although they aren't quite as chunky as the females. Still, it allows some Oil Beetles to produce up to 10,000 eggs. You need a lot of room to carry that kind of weight!

Video: Serbal Almeria

In some ways, Oil Beetles look even worse than the Leaf variety. Their body is much longer and bulges horrifically all the way down. Some are so long that half their body has to be dragged along the floor. They also have no wings, and the wing cases seem to have accepted a purely ornamental role and have shrunk right down so they barely cover anything at all.

On the other hand, at least the abdomen doesn't look quite as stressed and strained and ready to burst! With Leaf Beetles, their abdomen expands during their adult life and the skin around their abdominal, exoskeletal plates stretches so thin that it can become translucent. Sometimes you can just about see the eggs inside.

Video: Ausfild

Oil Beetles, on the other hand, are big and bulging as soon as they enter adulthood, so they don't have to stretch their skin to breaking point.

Speaking of entering into adulthood, one interesting thing about Blister Beetles is that they're hypermetamorphic.

Most of the insects that go through metamorphosis start out as some kind of larva, like a maggot or caterpillar, which eats and eats until it's big enough to pupate and develop into an adult.

Oil Beetles, like other Blister Beetles, are different. They have an entire, extra larval stage!

Image: Malcolm Storey
Triungulin larva

Their eggs hatch into tiny larvae known as triungula. They have a tough exoskeleton, eyes, six long legs and three claws on each foot. They look for all the world like some kind of louse. They act like it too!

The triungula start their life in a hole in the ground previously excavated by their mother. In some species, the triungula will climb out and simply scamper away in search of grasshopper eggs to feed on. In most species however, their mother has been careful to dig her nest near to those of ground-nesting solitary bees.

The bees pack their own nests full of pollen to serve as food for their young. In another world perhaps our Oil Beetle would have done that for her own children. But she doesn't have wings any more and besides, 10,000 mouths to feed is a lot of work.

Image: Malcolm Storey
Triungulin clinging to a bee

Instead, the triungula climb up nearby plants, settle down in the flowers and wait. When a bee comes by to gather pollen, they crawl onto it, grab hold with all those claws and hitch a ride all the way to the bee's nest. There they feast on the pollen. Also they eat the bee's larvae because really there are a lot of mouths to feed and if you will insist on being in the same place as where the food is...

Some Oil Beetles add insult to injury, or deception to murder. They're not interested in waiting about in a flower hoping that the right kind of bee will happen along. They take a more proactive approach to the whole affair.

Video: globalzoo

They don't go to the flowers, instead they gather together in writhing blobs near the tip of stalks and leaves. Together they produce a pheromone which mimics the one produced by a female bee who's interested in some male company. A male duly arrives. He must be excited beyond all reason or like, doesn't know what a bee-woman looks like, because he immediately attempts to mate with a ball of limbs and lots and lots of mouths to feed.

Image: Leslie S. Saul-Gershenz and Jocelyn G. Millar
Meloe franciscanu

The triungula climb all over the male bee and join him as he flies off in search of a real, live female. They're right there with him when he meets with romantic success, at which point they leave the male and crawl all over the female like something from a particularly ghastly STD awareness campaign. She eventually returns to her nest, where her terrible passengers disembark.

Image: Durlston Country Park

For the larval Oil Beetles all this is merely stage one. While they're in the bee's nest eating everything in sight, they develop into the flabby, eating-machines we usually associate with insect larvae. No more of this athletic, active triungulin scampering and scuttling all over the place. They almost completely lose their legs and their exoskeleton, and become soft, pale and not very good at walking anywhere. Which isn't much of a problem now that they don't have to walk anywhere.

After all that crazy it's back to good old pupation and adulthood. Phew!

Image: Yvan
Black Oil Beetle (Meloe proscarabaeus)

What a remarkable life history!

It has it all; sex, murder, deceit, betrayal, lice and more. And what a character arc! Who would think this bulging creature could have started out life as a minute louse racing up a plant so it can grab onto the hairs of a bee and hitch a ride? It doesn't seem possible. Even if they do look like they're full of helium.