The sting of love
Courtship in the animal kingdom has many faces. But sometimes the search for a mate may literally be painful.
One of the imperatives of life for all animals is to find a mate and reproduce. But rather than resorting to romance, some species' courtship rituals appear to include an assault of stings or bites.
Dr Ronald Jenner, venom evolution expert at the Museum, helps explain some toxic relationships of the animal kingdom.
It takes two
Several species of scorpion have a courtship ritual that appears to walk a fine line between wooing and attacking.
A male scorpion will lead a female on a dance-like walk, known as a promenade à deux, holding her by the pedipalps (large claws). During this waltz, males have been observed stinging their partners.
Ronald says, 'Sexual stinging occurs in lots of different types of scorpion. But nobody has ever figured out if the male injects venom or if the sting is dry.'
Some scorpion species have two types of venom: a 'pre-venom' that mainly contains salts and is used as a painful defensive sting, and a full venom, which is made up of proteins that can cause biological effects such as paralysing their prey.
'It is thought by some that sexual stinging only uses the pre-venom. But then there is the question of why. The majority consensus is that it calms the female down, because she is armed with a dangerous sting as well.
'Calming the female would allow the male to lead her. He puts his sperm package on the ground and she has to absorb that into her body - that needs choreography.
'So it could be that the stings make her receptive to the dance without becoming aggressive or running away.'
However, some scientists think the opposite - that the male's sting has a stimulatory role instead. There are species of centipede that engage in somewhat similar tactics.
All known species of centipede are venomous, and males of some species have been recorded as biting females during the mating - although, like with scorpions, the intention and effect are unclear.
Some land snails take a similar attacking approach. Certain species of hermaphroditic snail - which have both male and female reproductive organs - produce gypsobelum, often called love darts. These are typically made of calcium carbonate or chitin.
Watch as Jon Ablett, Senior Curator of Mollusca at the Museum, explains more about this relationship ritual.
The shape and size of the dart varies from species to species, but all darts transfer a sperm-boosting mucus into the chosen partner.
These snails mate with multiple partners, and the darts increase the chances for the sperm to fertilise as many eggs as possible, instead of being discarded by the recipient.
A 2015 study found that the darts shortened the lifespan of the darted snails and reduced their ability to produce offspring in the future.
It is not clear what causes this reduction, but it could be physical damage from being stabbed. This could lead to snails evolving defences against the darts, but also to more effective apparatus.
Jon Ablett and Alison Shean explore more about snail love darts:
Stinging, biting and other painful tactics aren't always a male-to-female affair. Some species use violent tactics in the arms race against competing males.
Male platypuses have sharp spurs on their hind feet. These are connected to a gland that produces a potent venom, reportedly excruciatingly painful in humans. Scientists commonly believe that male platypuses wield their venom in battles against each other over territory and females.
Ronald says, 'It has been noticed that a stung male can get temporary paralysis of the legs. There is definitely an adverse effect.
'Although there are some scientists who think that the male stings the female and it is so painful and unpleasant that she wouldn't want to mate with another male. This would heighten his chances of her having his offspring.'
Sea anemones are also known to sting their rivals. But for those that reproduce asexually, their assaults are to create space for their own offspring. The anemones can tell their own cloned polyps from foes, and will fire stinging cell organelles (called nematocysts) at their opposition.
Depending on the species, the venom can be highly destructive, causing necrosis and severe tissue decay. But for anemones, the intraspecific assault seems worth it when it comes to providing for their clones.
Venom isn't always used in stings and bites during courtship. Some wasp females use it as an aphrodisiac instead.
'In some wasp species the female flies up and squirts venom in the air from her stinger. It's a sex pheromone and it attracts males,' explains Ronald. 'The pheromone also induces copulation behaviour in the males.'
The purpose of venom in breeding is widely agreed upon for some animals, such as the platypus. But when it comes to sexual stinging and biting by arthropods, there is still much to learn.