Metoecus paradoxus and its Crazy Wasp Destroying Ecology

 

Whilst walking back from the car to the house I chanced upon this Metoecus paradoxus, sat precariously in the middle of the garden path and narrowly escaping being stood on. A quick glance at this insect probably provides a bit of confusion as to what family it actually belongs to. Despite it looking very much like a fly, it is actually a beetle, belonging to the Ripiphoridae (Wedge-shaped Beetles). This is the second time I have recorded it within the garden, after finding a male in a similar situation a few years ago, associated with a wasp nest (Vespula vulgaris) in our loft. This female appears to have come from a similar wasp nest in the garage this year. 

As if this beetle doesn't look strange enough, it has an equally interesting ecology. Metoecus paradoxus is a parasite of wasp larvae. It primarily is a parasite on Vespula vulgaris and Vespula germanica, but will use other species too. As this species requires social wasps it occurs in any habitat that they occur in, which is very wide ranging. Adults of these beetles are seen from around July to October, and are short lived with females generally living between 6 and 12 days and do not feed. In some situations large numbers of these beetles can emerge from wasp nests, with an example of over 500 found in a bungalow, associated with a wasp nest. 

Upon emergence females oviposit on exposed dead/dry wood, on which they lay clutches of 10-50 eggs inside crevices and cavities, and will produce several hundred eggs during their lifespans. These eggs overwinter and then hatch into long legged mobile larvae, the following spring. These larvae actively seek wasps coming to the wood to chew off wood to create their nest sites. Upon finding a wasp the larvae clings to its host and is transported back to the wasp nest, in some cases several of these larvae may hitch a ride on a wasp. 

Upon entering the wasp nest they search for a nest cell with a developing wasp larvae inside, and develops slowly alongside it as a largely inactive endoparasite inside the host. Once the host has moulted 4 or 5 times it bores out of its host, blocks the cell hole with moulted skins and attaches itself to the outside of its host and feeds on its fluids as an ecotoparasite. It then rapidly develops before consuming the entire host and eventually pupating in the nest cell. This whole process takes around 24 days. Once the adult emerges, usually in the morning, it chews its way out of the nest cell, exits the wasp nest very rapidly. As it leaves the cell the beetle secretes pheromones obtained from the wasp larvae to prevent wasps attacking it, it then exits the nest and the cycle beings again.