The surprising biological drive behind why butterflies congregate on mud and carrion

Nature · Published 18 October 2026 Swipe more like this →

In short: It is not just about thirst. For many insects, puddling is a high-stakes nutritional strategy. From drinking human sweat to extracting minerals from the tears of sleeping birds, these organisms seek out specific salts and amino acids to fuel reproduction and survival.

Puddling is a nutrient-seeking behavior where organisms ingest fluids from moist substances like mud, rotting fruit, or carrion. While most famous in butterflies, this behavior extends to leafhoppers, such as the potato leafhopper (Empoasca fabae), and even certain bees. The goal is the uptake of essential salts and amino acids, which are vital for physiology and ecology.

In many species, this behavior is male-driven. For example, male Speyeria mormonia puddle much more frequently than females. The nutritional benefits are significant: males often transfer collected sodium to females via a spermatophore during mating, acting as a nuptial gift that enhances egg survival. This drive can even lead to social aggregation; the presence of a group can act as a stimulus for species like Battus philenor to join the flock.

The sources of these nutrients can be quite macabre or even invasive. Some insects, known as lachryphagous, drink the tears of animals. The moth Hemiceratoides hieroglyphica has been observed inserting its proboscis into the closed eyelids of birds in Madagascar, while others, like the genus Calyptra, are known as 'vampire moths' for sucking blood from vertebrates. Even stingless bees in the Lisotrigona and Pariotrigona genera visit mammalian eyes, sometimes causing human distress.

The mechanics of processing these fluids are extreme. In the male notodontid Gluphisia crenata, fluid can be released from the anus in forced jets every three seconds. The volume is staggering: up to 600 times the insect's body mass may pass through the digestive tract. This high-throughput system is supported by males having a much longer ileum than non-puddling females.

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