September 2018

Underneath our apple tree are a large number of windfalls varying in state from eatable to completely rotten.  One reason (excuse?) for leaving them there is that it feeds the wildlife.  One of the main species to feed on the apples are wasps, but I was delighted recently to see a hornet cruising around the windfalls.  I was delighted because though they may be fearsome to some, to me they are a magnificent insect.  I have seen hornets feeding on the apples in the past, but this one had a different purpose in mind.  It flew towards an apple on which a wasp was already feeding.  There followed a surprisingly lengthy scrap between the two insects, but the outcome was never in doubt and by the time I got back with my camera, only the abdomen of the wasp remained.  Not sure whether there was any life left in it, I carefully nudged it onto a handy leaf and carried it out of the shade of the tree to get a better look.  I was wise to be so careful because within a minute or two, the abdomen suddenly started to try and sting anything within reach.  Clearly the hornet had stung the wasp to subdue it but the effect had gradually worn off.  A careful examination of the grass under the tree revealed several more stray wasp abdomens which suggests that wasps are a large part of the hornet’s diet.  I am guessing that it takes the head and thorax because there is more protein in the thorax due to the leg and wing muscles being in there.  

Wasp abdomen - still dangerous

European Hornet Vespa crabro about to behead a hoverfly 

Apparently a hornet sting is no more painful than a wasp or bee sting, each rated at level 2 on the Schmitt pain index, and each lasting around 10 minutes.  The pain index was compiled by the American entomologist Dr. Justin Schmidt, who wanted to know if social insects had evolved better defences than solitary insects because of their greater investment in the colony.  He allowed himself to be stung by more than 80 different species in order to compile the index.

On a similar note, we thought we had seen several hornets feeding on ivy flowers when we visited Kew Gardens recently.  Closer examination showed that they were in fact Hornet Hoverflies.  This insect also goes by the catchy title – Volucella zonaria.  It is a very convincing mimic and Britain’s largest hoverfly and is an example of what is called Batesian mimicry where a harmless species evolves to look like a much more dangerous species to avoid being eaten by predators.  This type of mimicry is named after a Victorian entomologist Henry Bates who first described the phenomenon.  He was a contemporary of Charles Darwin, and travelled to South America in 1848 with Alfred Russel Wallace who came up with the theory of evolution at around the same time as Charles Darwin.  Wallace returned from the Amazon four years later, but Bates stayed and studied mostly the insect life there for another 7 years, sending back thousands of specimens, many of which were new to science.  His collection survived the crossing back to Britain and in that he was more fortunate than Wallace, whose collection was destroyed by fire in a shipwreck on the journey back.  Bates wrote a very interesting book about his experiences – The Naturalist on the River Amazons – which is a classic of nature travel writing.  The hornet hoverfly also uses its mimicry in another way – to escape detection when it lays its eggs in the nests of hornets, wasps and bees where the larvae eat detritus around the nest.  A dangerous strategy indeed.

Hornet Hoverfly - Volucella zonaria