Dark Tales of an Ichneumon Wasp Lifecycle
11 November 2020
Dorothy Baynham was intrigued after reading about Ben Mullen's Ichneumon record last week. This inspired Dorothy to write a piece about her observations over the summer and she has also included some very interesting photographs.
I have had the photograph and information given by Dorothy checked by the Senior Curator of Hymenoptera in the Natural History Museum, Gavin Broad, and he is happy with the identification of this species of Ichneumon. These wasps will apparently parasitise the butterfly cocoons of Large White butterflies.
Over to Dorothy....................
After seeing Ben Mullen’s very rare Ichneumon wasp on this blog I recalled that I had
photographed Ichneumon wasps in my garden throughout the summer (2020). My wasps were not rare - just a common parasitising wasp, Cotesia glomerata, the scourge of the Large (Cabbage) White butterfly. Here is the adult wasp (below).
Cotesia glomerata, Dorothy Baynham
The wasps lay their eggs in the caterpillars of the Large White butterfly by impregnating them
as soon as they emerge onto the leaf of the host plant – usually brassica leaves.
Large White caterpillars, Dorothy Baynham
After 2 or 3 weeks the wasp eggs hatch inside the caterpillar, which has now grown in size, and
the wasp larvae eat parts of the body of the caterpillar, leaving vital organs intact so as not to kill it.
When fully grown the wasp larvae burrow through the skin of the caterpillar, and emerge into the outside world.
Copyright Dorothy Baynham
The wasp larvae then develop yellow cocoons. The caterpillar, still alive, spins a silken web
around the cocoons to protect them and stands guard over them. Eventually, through weakness and lack of food it dies and drops to the ground.
Copyright Dorothy Baynham
After about a week the adult wasps hatch from the cocoons and the life-cycle starts all over again.
Copyright Dorothy Baynham
This, although rather macabre, seems fairly straightforward but I was left with a few questions
which, so far, I have been unable to find answers. One Large White caterpillar, after climbing up
the wall alongside my garden, managed to successfully develop into a chrysalis.
Copyright Dorothy Baynham
The photo above shows the chrysalis and what look like wasp larvae or eggs protruding ever so slightly from a crack in the casing. If that is what they are, I am curious to know whether the Large White caterpillar was invaded by the wasp before it reached the chrysalis stage or was it parasitized while a chrysalis?
Copyright Dorothy Baynham
This picture above shows wasps taking an interest in the chrysalis but whether they were trying
to find a way in or were just curious it is impossible to know. After some time the chrysalis fell from its position on the wall to the ground below. It was empty but there was a hole, that I hadn’t
noticed before, at the front end.
Copyright Dorothy Baynham
Could the wasps have developed inside the chrysalis and emerged as adults through the hole in the chrysalis?
All the more reason to keep a closer look next year to maybe find some answers.
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What a fascinating natural history journey! Thank you Dorothy.
According to Gavin Broad, the Natural History Museums Senior Curator of Hymenoptera:
''Butterflies and caterpillars frequently host parasitoids, insects that attack and destroy their hosts, sometimes eating them alive. These are usually wasps, laying their own eggs inside an egg, caterpillar or pupa.
Parasitoids start their lives as parasites, in or on the body of a host, but they end up as predators, eating the host entirely''.
To read more about parasitoid wasps, please go to:
https://www.nhm.ac.uk/discover/body-snatchers-eaten-alive.html