Name: Asian hermit spider (Nephilengys malabarensis)
Where it lives: South, Southeast and East Asia (including India, Sri Lanka, the Philippines, China, Japan and Indonesia)
What it eats: Moths, beetles, flies, crickets and other small insects
Why it’s awesome: The Asian hermit spider is no ordinary arachnid. This spider has evolved an adaptation that allows it to reproduce while escaping the threat of female cannibalism: It can detach its penis.
This spider species displays extreme sexual dimorphism, meaning that males and females have significantly different appearances. Females can grow up to around 0.59 inches (15 millimeters), while males are less than 0.20 inches (5 millimeters).
Males face considerable risks during mating due to aggression from females, which may kill and eat their partners before or after mating. Sex can be so treacherous for the males that they have developed the ability to detach their penis so they can leave it pumping sperm while they flee to safety.
In this process of “remote copulation,” a male spider’s palp — its sperm-delivering organ, of which it has two — can break off inside the female’s reproductive tract. The broken-off palp can remain inside the female and continue pumping sperm into her even after the male has escaped.
While studying this “eunuch phenomenon” among orb-web spiders, biologists discovered that the longer the severed palp is left in the female genitals, the more sperm it transfers. And palp breakage induced by the female, instead of the male, led to faster sperm transfer.
The detachable penis also serves another important function: It acts as a mating plug. After breaking off, the embolus — a needle-like structure that delivers the sperm — stays lodged inside the female’s reproductive opening to prevent other males from mating with her. This reduces sperm competition and increases the likelihood that the male’s genes will be passed on.
After losing its penis, the male spider also becomes more aggressive and guards the female from other males that might try to dislodge the “palp plug” and inseminate the female.
According to a 2011 study in the journal Animal Behaviour, removing one palp reduces the spider’s body weight and increases its endurance, thereby boosting its ability to fight. This finding supports what the researchers called a “gloves-off” mating strategy, where the spiders have nothing to live for other than protecting their potential offspring.
The male spiders also have another trick to prevent being eaten by the females: Sometimes, they offer one of their legs to the female as a distraction during mating. This act of self-amputation, known as autotomy, reduces the risk of being attacked or eaten during the mating process. It can also buy the male time to escape.
