A very large (3 cm body length) sawfly, vaguely resembling a hornet but fatter bodied. The larvae are up to 50mm, yellow/green with blue dots along the sides and large dorsal stripe.

Cimbex luteus is a similar size but has the basal three tergites maiinly yellow, whereas these are mainly dark in C. connatus.

Around alder species, sometimes Italian Alder planted in city centres and supermarket car parks.

Mid to late summer.

The larvae feed on various alder species. When fully grown, they are about 50 mm long and have a dark dorsal stripe all the way along the body. They generally feed between July and September, but may still be found as late as October.

Uncommon but expanding its range.

Rare in Leicestershire and Rutland (VC55).

https://www.sawflies.org.uk/cimbex-connatus/