The BMSB is a large shield bug, a similar size to several native species. It has generally brown and marbled coloration. The key features to distinguish the adult from other native shield bugs are its rectangular-shaped head and rows of pale dots across the body behind the head. It also produces a distinctive smell resembling coriander plants and, when it is present in high numbers, this may be considered unpleasant and disturbing. The juvenile stages (nymphs) are easier to recognise because, unlike any native shield bugs, they have spines on the sides of the body.

Adults have been intercepted in imported goods and luggage and a few individuals found free out of doors in England but so far other life stages (nymphs or eggs, confirming breeding) have not been found.
In 2022, a female, found in South East England, laid eggs after capture, though these were unviable. This suggests that the shieldbug may become established, especially with warmer summers which favour the insect.

The BMSB has a very wide host-plant range, feeding on more than 100 plant species, including important crops such as apples and brassicas alongside many ornamental and woody plants. It is a very mobile insect, which likes to move and feed on the

Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding.