Male spider mites strip off female skin to mate sooner

In many species, males have a strong incentive to identify females who are about to reach sexual maturity in order to have the first chance at mating. Recently, researchers published a study in the journal iScience revealing a fascinating example of this behavior: male spider mites actively engage in guarding and stripping off the skin of immature females who are on the verge of molting and maturing, thereby accelerating their accessibility for mating.

Peter Schausberger, a scientist from the University of Vienna, Austria, described this behavior as extraordinary within the animal kingdom. He emphasized that the male spider mites’ action of undressing the premature females is adaptive, meaning it enhances their reproductive success. If a rival male were to seize the female and inseminate her instead, it would be a significant loss for the male who invested time and effort in guarding her. The guarding males spend hours protecting a potential future mate without any guarantee of a reward.

The competition for the first opportunity to mate is particularly fierce among spider mites. This is because the first male to copulate with a female fathers all of her offspring. It is noteworthy that male spider mites only sire daughters, as sons are produced from unfertilized eggs. Due to this intense competition to be the first, male spider mites diligently guard immature females for several hours before they molt into adulthood.

A key indicator that a female spider mite is about to molt is her silvery appearance, which arises from the air filling the gap between the old skin (exuvia) and the new skin. During this phase, the guarding males alter their behavior. They sometimes drum their forelegs on the females, possibly to stimulate the molting process, causing the females to bulge and crack the exuvia.

Spider mite undressing. Credit: iScience/Schausberger et al.

Once the exuvia is cracked, the male spider mite becomes extremely active and uses his pedipalps to pull on the hind part of the old skin, removing it from the female’s body. This exposes the female’s genital opening, located on the underside of her abdomen, allowing the male to position himself beneath her and insert his aedeagus for mating.

Peter Schausberger and his colleagues, who have a general interest in sexual selection and alternative reproductive tactics in spider mites, made these observations while studying male-male and male-female interactions. They were intrigued by the undressing behavior and extensively documented its details.

The researchers consider these findings as another captivating example of behaviors driven by sexual selection. They also emphasize that even tiny arachnids exhibit highly sophisticated behaviors.

In future studies, they plan to investigate the undressing behavior further to determine if fighting males exhibit differences compared to sneaking males. Additionally, they aim to explore how male-male competition influences the undressing process and whether undressing behavior serves as a signal to females regarding a male’s quality.

Source: Cell Press

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