A lemur carefully manipulating a toxic millipede is one of the most unusual examples of animal behavior observed in Madagascar. Documented most often in species like the Red-fronted brown lemur (Eulemur rufifrons), lemurs deliberately provoke the arthropods to release potent chemical secretions. They then apply these secretions to their bodies in a process called self-anointing. Scientists question whether the lemurs are seeking pharmacological relief, a temporary state of altered consciousness, or both.
Observing the Unusual Behavior
The process begins when a Red-fronted brown lemur, or sometimes a Black lemur, locates a millipede, often from the genus Sechelleptus or Spirostreptus. The lemur handles the millipede with care, biting it lightly or rolling it to agitate it without crushing it. This agitation causes the millipede to excrete a visible orange or yellowish defensive fluid.
The lemur then actively rubs this secretion onto its fur, focusing on areas where parasites are most prevalent, such as the tail, anogenital region, and inner thighs. This topical application can last for several minutes, often involving repeated biting and rubbing of the millipede.
Following the anointing ritual, a noticeable change in the lemur’s demeanor often occurs, including profuse salivation, a partially opened mouth, and a seemingly relaxed or lethargic state. In some instances, the lemur will consume the millipede entirely after applying the secretions externally, suggesting the compounds serve both external and internal functions.
The Source of the Effect: Millipede Chemical Defenses
The millipedes favored by the lemurs produce chemicals as a defense mechanism against predators. The most significant components are quinones, particularly benzoquinones, which cause the orange color and pungent odor. These benzoquinones are highly volatile and act as strong irritants and insect repellents.
The secretions also contain traces of hydrogen cyanide (HCN) and compounds like hydroquinones and cresols. Although cyanide is present, the millipedes release it in small amounts, and the lemurs’ careful biting likely controls the dosage. Benzoquinones are the primary chemicals believed to cause the psychoactive effects observed.
The lemurs handle these substances without severe harm due to their careful application method. This maximizes topical exposure while limiting ingestion to small, controlled amounts. The resulting intoxication is a temporary, non-lethal side effect, repurposing chemicals designed to deter predators for the lemurs’ benefit.
Analyzing the Purpose: Self-Medication or Intoxication
Scientists have developed two main hypotheses to explain this behavior: pharmacophagy (self-medication) and recreational intoxication. The self-medication theory proposes that the secretions are a form of natural medicine. Benzoquinones are known to be effective against external parasites, acting as an insecticide to repel or kill ticks, mites, and mosquitoes.
This hypothesis is supported by observations that the lemurs often perform this ritual during the rainy season when parasite populations are highest. The application is frequently directed at the perianal region, a common site for the eggs of parasitic pinworms (Oxyuridae nematodes). Ingesting the millipede may also help fight internal parasites by slowing their growth in the gut.
The intoxication hypothesis suggests that the psychoactive properties of the benzoquinones are the primary motivator. The observed lethargy, drooling, and relaxed posture indicate a temporary state of euphoria or altered consciousness. This feeling of a “buzz” might reinforce the behavior, making the lemurs seek out the millipedes even when the parasitic threat is low.
The behavior is likely driven by a dual function, offering both a medical benefit and a rewarding neurological experience. This combination of practical relief and intoxication makes the ritual a highly adaptive behavior for the lemurs in the Madagascan forest ecosystem.