Sinea diadema is a species of assassin bug family (Reduviidae), in the subfamily Harpactorinae.

Sinea diadema is bivoltine, preys on small bugs and beetles, and overwinters in the egg stage.

In English the species goes by the common name spined assassin bug.

However, when it occurs it usually involves a larger female eating a smaller male.

[5]: 94 It is native to North America and found in the Midwest in fields, often associated with goldenrod Solidago missouriensis Nuttall.