Stink bugs belong to the insect family Pentatomidae, commonly referred to as “shield bugs” because of their distinct body shape. These insects are recognizable by the unpleasant odor they release when threatened or disturbed. While the scent is often the first thing people notice, the adult size of these common household pests frequently surprises those who encounter them indoors. Their dimensions are a result of a specific growth pattern and body structure that makes them seem larger than many other insects of similar length.
Maximum Size of Common Stink Bug Species
The maximum size a stink bug can attain varies depending on the species. The most frequently encountered species in North America, the Brown Marmorated Stink Bug (BMSB), represents the larger end of the spectrum for common pests. Adult BMSBs generally measure between 14 and 17 millimeters long (approximately 0.5 to 0.75 inches). The maximum length for this species has been documented to reach up to 19 millimeters, or about three-quarters of an inch.
These adults often measure around 8 millimeters across their broadest point. When compared to other common types, the adult Green Stink Bug, for example, typically measures slightly less, around 12 to 13 millimeters in length. The Brown Marmorated Stink Bug’s combination of length and breadth contributes significantly to its appearance as a large insect.
Factors Contributing to Perceived Size
The impression that a stink bug is large is influenced by its unique body structure, which is broad and flat. Unlike many other insects that have cylindrical or elongated bodies, stink bugs possess a pentagonal, or shield-like, outline. This wide, flattened carapace gives the insect a substantial surface area relative to its actual linear length.
The body width is often nearly equal to the body length, a trait that visually maximizes the insect’s overall footprint. Their six legs extend outward from the sides of the broad body, creating a larger perceived diameter when the insect is resting on a surface. This combination of a wide shield shape and laterally extended legs makes the insect appear larger than a narrow-bodied insect of the same measured length.
The Stink Bug Growth Process
A stink bug achieves its final adult size through incomplete metamorphosis, which involves three life stages: egg, nymph, and adult. The nymph stage, where all growth occurs, consists of five phases, each known as an instar. The insect must molt, or shed its exoskeleton, to progress from one instar to the next and increase its size.
When the nymphs first hatch from the egg, they measure only about 2.4 millimeters in length. They are wingless at this stage and grow incrementally through the five molts. By the time the nymph reaches its fifth instar, it has grown to about 12 millimeters and is nearly the size of a fully developed adult. The final molt transforms the large nymph into the full-sized adult with functioning wings, at which point the insect stops growing completely.