Under the cover of darkness, a secret army is on the march. Each evening, as the sun fades, thousands of warty foot-soldiers make their slow progress back to their birth pools.

This migration would go largely unnoticed if it wasn’t for the carnage that is left behind when their world collides with ours.

For at this time of year, many of the highways and byways criss-crossing the UK are littered with the corpses of toads.

An estimated 20 tonnes-worth of toad meet their fate on our roads each year.

The reason for this amphibian Armageddon is relatively straightforward — sex.

In early spring, toads emerge from the protection of their winter quarters to return to the ponds of their birth for a spot of noisy and generally rather shambolic procreation.

Male toads, when in an amorous mood, can become blinded by lust. They arrive at the ponds earlier than the females and get rather worked up.

When the females do finally put in an appearance, it’s not unusual for excitable males to clasp on to passing fish or other generally unresponsive inanimate objects in a mad-cap mating frenzy.

Several may grab on to the same female — creating a large and chaotic ball of churning toads.

The toad (Bufo bufo) is a very site-loyal beast. Many travel back to the location of their birth and this site fidelity is where the problems begin.

Sam Taylor, from amphibian charity Froglife, said: “Toads are generally incredibly faithful to their breeding ponds, and make this massive effort to get back there. They will take quite specific routes too, it’s not always ‘as the crow’ flies.

“The things that make a good toad breeding pond are quite specific — they tend to like deeper, larger ponds than other amphibians. There would also be no point in one toad sitting in one pond on its own, so mass migrations make sense from a breeding point of view.”

To reach these sought-after sites, toads generally have to cross the odd road or two, and if a particularly good pond is near a busy road, then large numbers are destined to become road casualties.

In an unfortunate biological quirk, toads prefer to travel at dusk — just as human rush-hour is getting into full swing and our roads are at their most dangerous.

Taylor said: “The toads generally start to move at dusk, which is part of the problem as at this time of year that’s about 5.30-6pm, so their rush hour clashes with ours.

“They particularly like mild damp evenings and will continue moving into the night, depending on the temperature.”

But surely the occasional road casualty can’t really pose a serious risk to our toads? Well, actually it can.

The number of new roads and new drivers continues to expand while the number of suitable toad habitats continues to fall.

Thousands of toads are being run over each year, and recent studies suggest road deaths could be a factor in local declines.

But all is not lost. Each year, dedicated groups go to great lengths to ensure that many of our toads do get across the roads safely.

Froglife’s Toads on Roads scheme harnesses the goodwill of bucket-carrying volunteers or “toad patrollers” who wait at hotspots to scoop up the amphibians and lift them to safety.

More than 800 migratory crossings have been identified by the scheme across the UK.

Anyone can register a toad-crossing site and if the location attracts more than 100 toads, a road sign can be erected to warn drivers they are in a toad zone.

But even at monitored toad crossings the amphibians aren’t always safe.

Taylor added: “The volunteers report that they find approximately one dead toad for every nine that they are able to move across the road.

“At sites where there are no volunteers or it’s too dangerous for people to go out at night and help the toads, the figures will again be much higher.”

The toad has been declared a Biodiversity Action Plan priority species, which should, in theory, afford it greater protection and many new roads in known hotspots are now built with a toad tunnel to enable safer migration.

We can all do our bit to help toads out of a hole — next time you are behind the wheel, keep your eyes on the road and spare a thought for these precious pedestrians.

n For more information on Froglife’s Toads on Roads scheme, visit www.froglife.org/toadsonroads