A warm winter and spring followed by a mild and rainy summer has created perfect breeding conditions for the fleas – including mutant ‘porn star’ fleas – dubbed because their penis is two and a half times longer than their body.

The critters are currently in the midst of their breeding season with males rushing from female to female, with the female fleas giving birth at an incredible rate.

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Fleas with giant penises are set to invade Sheffield.

The sheer number of fleas mean homes and offices can quickly become infested with the creatures being carried into homes on cat and dog fur.

The beasts then set up home in carpets and furniture and can go on a mating frenzy, leading homes to be quickly overrun with the bugs which can bite, leaving itchy spots on humans.

A spokesman for pest controllers Basis Prompt said fleas thrive in a warm and humid environment – with numbers set to peak in the coming weeks.

"The population of fleas seems to have grown rapidly in recent years, but the risk of an infestation could be bigger than ever this summer."

A female can lay up to 50 eggs a day and fleas can bury themselves in carpets and soft furnishings and beds.

Scratching pets are often the first sign of infestation – but humans should look out for red blotchy rash marks and spots around their feet and ankles.

Pets can be given anti-flea treatments from a vet, but it's vital to thoroughly clean bedding, sofas and furniture, floors and skirting boards.

Bites should be washed with soap and water and then an antiseptic cream should be applied.