A Caterpillar

Why is the caterpillar on the broadbean plant at the allotment plot in February? Where has it grown from? Surely no butterfly has fluttered by and perched long enough to deliver eggs that have then grown over a week into a fat caterpillar? Or has the caterpillar overwintered on the broadbeans surviving the chill of winter, choosing not to turn into a crysalis or to evolve into a moth or butterfly? Was the caterpillar found by a passing bird that spied a worm so dropped the caterpillar into the broadbean leaf to cradle? The multiplicity of event occurs and mystery at the allotment plot.