Some people imagine that all life was created by some sort of "God"........well there is no evidence thats its true and in any case, what kind of "God" would have created......
The Warble fly......
http://en.wikipedia.org/wiki/Warble_fly
My previous examples were of parasites that affected humans.......but other creatures are tortured as well.........we used to treat for it when I was a kid on my dads farm. It has since been eradicated from many Countries.
The fly will lay eggs on the foreleg of the affected cattle. These will be ingested by licking, and be swallowed. Internal cycle involves the passing oesophagus muscles and spinal cord before subcutaneous re-emerging.
When they re-emerge, the larvae cause many swellings ("warbles") under the skin, causing some harm to animals, but not as a general disease. It doesn't burrow into the flesh, but stays under the skin (hence, its scientific name Hypoderma). Nevertheless, when accidentally destroyed by pressure, the larvae can cause large purulent swellings.
From the subcutaneous swelling, the warble will puncture the skin when coming out of the bovine. From those numerous holes, the hide is rendered valueless.
The migrating larvae can cause damage to meat as the tunnels they make fill with a substance known as butcher's jelly.[1] Growing livestock may have a lower daily weight gain. Milk yields may also suffer, but in adult cows, the infestation is generally limited, due to immunisation following the first infestation, as a calf.