This item comes from David Attenborough's TV series "Life in the Undergrowth" which has a wonderful segment on the unusual progeny rearing practices of the Blister beetle. What staggering coincidences stacked up to allow this chain of behaviour to evolve in the first place and what a slim chance in any individual case for Blister beetle lavae to see adulthood.
The following seven photos are all screen shots from the BBC series "Life in the Undergrowth".
The female Blister beetle lays hundreds of eggs in a hole in the Californian desert and leaves - parenting job done.
After six weeks the eggs hatch into 2mm long lavae and proceed to climb to the top of the nearest stalk of grass where they all cluster to form a bee sized lump giving off the perfume/pheromone of the female Digger bee.
If they are lucky a keen male Digger bee, mistaking the cluster for a mate, alights briefly. Those lavae who can, quickly latch onto the body of the male bee.
Male Digger bee takes off and hopefully then strikes the real thing - mating with a female Digger bee. The Blister lavae simultaneously jump ship and now cling to the Digger female.
Mrs Digger eventually heads back to her nest, the lavae make their final jump and proceed to consume the Digger bees store of pollen put aside for her own lavae then, when the pollen has all been eaten, they eat the lavae of the Digger bee as well before happily proceeding with their own lifecycle.
You can see the complete 5 minute clip (taken from Youtube) from the series here.
A little related trivia: There are over 7000 species in the family of Blister beetles. They all have the ability to secrete cantharidin - a skin blistering chemical - as a defensive measure. This substance is collected commercially by drying and crushing the beetles and is sold as a wart remover. It is also used to induce farm animals to mate by irritating the urethral passages causing a prolonged erection. The particular beetle favoured for this latter purpose is Lytta Vesicatoria otherwise known as Spanish Fly. Also known to have been used by men. Unfortunately (for men) there is a very fine line between a dose sufficient for the intended purpose and permanent damage to the genitals or fatal poisoning.
This photo of Lytta Vesicatoria appears in Wiki Blister beetle article and is attributed to Ramona - Flickr username amiinsidemyself.
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