A male spider mite guarding a female
Peter Schausberger, University of Vienna
Male spider mites keep a close eye on young females and tear off their outer skin once they reach adulthood so that they can mate with them first.
Spider mites with two spots (Tetranychus urticae) are a common agricultural pest, feeding on a wide variety of crops, including beans and tomatoes. The mites shed their outer skin as they transition from young nymphs to adult nymphs – a process known as molting.
Adult females can have multiple sexual partners, but only their first mate’s sperm fertilizes their eggs. As a result, there is strong competition between males for females that have just reached maturity.
To try to secure this entry, male mites often guard young females until they become fertile adults. This is a risky strategy because it consumes energy and prevents the males from foraging for food – and rival males can still steal the females at the last minute.
Peter Schausberger at the University of Vienna in Austria and his colleagues found that male guards try to minimize this risk by stripping the outer skin off females just as they approach adulthood so they can inseminate them before other males swoop in.
The researchers filmed young female spider mites that were reared individually in cages with or without the presence of a male.
The females housed without a male naturally shed their outer skin at a leisurely pace when they reach sexual maturity.
In contrast, females housed with a male had their outer skin forcibly removed. When a female matured, the male would start drumming on her skin to encourage breaking open. Then the male used his mouthparts to peel off the female’s skin from behind so that he could expose her genitals and immediately inseminate her.
This meant females with a male emerged from their skins an average of 5 minutes earlier than single females, Schausberger says.
“Five minutes is not long in absolute time, but it is in relative time because these spider mites often live in densely populated colonies where other males are around,” he says. “Every second pays off when it comes to being the first with the emerging female.”
The spider mites are the first species in which this skin-stripping behavior has been experimentally documented, says Schausberger.
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