Oxford researchers have discovered the macabre way a parasite disguises itself as a layer of body tissue belonging to the insect it lives in.

The strepsiptera lives inside ants, grasshoppers and crickets but until now it has not been known why its insect host's immune system has not destroyed it.

Scientists at Oxford University's zoology department have found that it wraps itself in the host's own body tissue, leaving it undetectable.

Dr Jeyaraney Kathirithamby started studying the bacteria because she was mystified by the way it flourished without being attacked.

She found that its larva entered an insect by repeatedly jabbing its head against the host's cuticle -- the waxy layer above the skin -- until it could burrow inside.

It continued to wriggle to separate the skin from the interior cuticle, until the skin enclosed around it to form a self-contained bag.

The camouflage bag is not detected by the insect's immune system because it is identified as part of the host, so the larva can move deeper into its body.

Observations showed that the bacteria can grow, moult and absorb all the nutrients it needs through the bag of skin. Dr Kathirithamby said: "Parasitoids have evolved a variety of strategies for overcoming the host immune response.

"The mechanism of camouflage adopted by strepsiptera has not been observed before, and is yet another fascinating feature of these unique parasites."