After an absence from the records of 32 years, the large velvet ant (Mutilla europaea) has been sighted again in Scotland by Dr Jenni Stockan from the James Hutton Institute. Athayde Tonhasca reveals the idiosyncrasies of this surprising insect.
Velvet ants are so called because of the dense ‘hairs’ (setae is their proper name) covering their bodies. However they are not ants at all – they are wasps.
The females of this wasp family (Mutillidae) are wingless, so it is not surprising that they are mistaken for ants. The males do have wings and fly about in search of pollen and nectar, but are rarely seen. Some velvet ant species exhibit extreme sexual dimorphism, which means that males and females look very different. So much so that it is often very difficult to pair up males and females belonging to the same species, unless they are captured while mating.
All velvet ants are parasitoids of other insects, that is, they spend part of their lives inside the body of their hosts. After mating, the female wasp invades an insect nest, typically a ground-dwelling species of bee, fly, beetle or butterfly. In the case of the large velvet ant, their hosts are various bumble bee species and occasionally honey bees. The female deposits her eggs inside bee pupae, which the velvet ant larva then eats. Males leave the host nest soon after they emerge, but females sometimes remain there throughout the winter.
Studies in Italy have shown that large velvet ants are also cleptoparasites: they sneak into the nests of the paper wasp Polistes biglumis to steal their food. It is believed that they get away with it because they have developed the ability to disguise their scent and therefore go undetected by their victims.
But there are more tricks in the velvet ants’ bag: when threatened they stridulate, meaning they produce noises by rubbing together different sections of their body. These sounds are no more than faint squeaks to us, but must have a stunning effect on creatures of their own size. On top of this, they are exceptionally strong and thick-skinned; they are not easily crushed, and in America have been reported to force their way out from the mouths of predators such as lizards and frogs.
Velvet ants are also known as ‘cow killers’, which is a completely inappropriate name. Although their stings are known to be painful, they are not dangerous. In fact, velvet ants’ venom is about 25 times less toxic than that of the honey bee. Moreover, females are not aggressive, and will only sting if handled.
The large velvet ant is quite rare in the UK and probably declining. Elsewhere, it can be found in Europe, the Near East and North Africa.