Giant Willow Aphids are dark brown with a peppering of black spots but can appear grey from a white dust which forms on them. It is an unusually large aphid, measuring up to 6mm long. Adults of the species have a thorn-like tubercle which protrudes from its back. As with other species of aphid, some giant willow aphids are winged; an adaptation believed to emerge in reaction to environmental pressures. Found primarily in large colonies on the trunks and branches of willow and sallow trees, the aphids splay their back legs and kick in response to potential threats.

On Willows

Although most common in the summer, this species can be seen in most months of the year, sometimes persisting into the winter.

Giant willow aphids appear to reproduce entirely asexually.

Thoght to be widespread and fairly frequent in southern Britain at least.

Thought to be fairly frequent in Leicestershire and Rutland.

https://influentialpoints.com/Gallery/Tuberolachnus_salignus.htm