Theridion grallator, also known as the “happy face spider,” is a member of the Theridiidae family. The Hawaiian name is nananana makakiʻi (face-patterned spider). The binomial grallator is Latin for “stiltwalker”, reference to the species’ long spindly legs. The spider is about five mm long overall.
Certain morphs have a pattern uncannily 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 pattern may change according to what food the spider has eaten (Gillespie, 1989) and as T. grallator is very small, hides during the day, and is thus not a significant prey item for any species of predator, it is more likely that the bizarre variety of patterns serves no significant adaptive purpose at all.