Asian Shore Crab

H. sanguineus has a squarish carapace, 2 inches (50 mm) in width, with three teeth along the forward sides; its pereiopods are marked with alternating light and dark bands. The males have a bulb-like structure at the base of the movable finger on their claws. Other distinguishing features include three spines on each side of the carapace. Adult sizes range from 35–42 mm width. These crabs are opportunistic omnivores that tend to favor other animals over algae. As crab density in an invaded area increases, so does the breadth of the species' diet, which suggests that competition alters selection of food. There currently is no mitigation against these crabs. A natural enemy of H. sanguineus is Sacculina polygenea, a parasite that attacks adult shore crabs and is specific to H. sanguineus.

Typically, the crabs live in areas with large rocks, such as between boulders on rocky shores. Hemigrapsus sanguineus inhabits many artificial structures such as on oyster reefs. H. sanguineus can tolerate other habitats, such as salt marshes.

Because the crabs are opportunistic omnivores, they will eat anything they can get their mouths around. H. sanguineus prefers to consume animals, but during a period of starvation, these crabs tend not to show a food preference. Most of the animals consumed by H. sanguineus are small invertebrates, such as mussels, snails, and amphipods. The diet of these crabs is overall very broad.

Hemigrapsus sanguineus is an "opportunistic omnivore" that prefers to eat other animals, especially molluscs, when possible. It tolerates a wide range of salinities (euryhaline) and temperatures (eurythermic).

Females produce up to 50,000 eggs at a time, and can produce 3–4 broods per year. The eggs hatch into zoea larvae, which develop through four further zoea stages, and one megalopa stage, over the course of 16–25 days. The eggs typically hatch in late summer or fall, into larvae, and the juvenile crabs molt in five stages to become megalopae, which typically takes about a month. Once in this stage, the crabs settle and metamorphize into full-grown crabs. The larvae are planktonic, can be transported for long distances during their development into benthic adults.