Theridion grallator, also known as the Hawaiian happy-face spider, is a spider in the familyTheridiidae. Its Hawaiian name is nananana makakiʻi (face-patterned spider). The specific epithetgrallatoris Latin for "stilt walker", a reference to the species' long, spindly legs.
The spider is up to 5 millimetres (0.20 in) long. Certain morphs have a pattern resembling a smiley face or a grinning clown face on their yellow body. Each spider has a unique pattern, and the patterns differ from island to island. Some lack markings altogether.
On the island of Maui, the happy types seem to follow simple Mendelian inheritance rules, while on other Hawaiian islands the body inheritance patterns seem to be sex limited, The variation is possibly a kind of camouflage against birds, their only natural enemies of significance, to counteract pattern recognition by predators. As the background color may change according to what food the spider has eaten and as T. grallator is small, hides during the day, and is not a significant prey item for any species of predator, it is possible that the large variety of patterns serves no significant adaptive purpose.