Warning signs for box jellyfish have been posted at Waikiki and Ala Moana beaches this morning.

The monthly influx of stinging invertebrates was heralded this morning by the Honolulu Emergency Services Department this morning.

Box jellyfish are so named for the squarish shape of their bell-shaped body and can reach up to 2 inches and diameter and 3 inches in height, according to the Waikiki Aquarium. Although the sting of Hawaii’s box jellies is not usually lethal, it is reported to be more painful than that of the more common Portuguese man-of-war.