Aug 302020

Well I did ask! In a previous post I said that I only had 85 photographs of cinnabar caterpillars and that I needed more. So Alison promptly decided that she would send me one of her photographs. And here it is. The ragwort plant was growing in her lawn and she did not know the caterpillars but thought that they were beautiful. So she took a picture with her phone. As I have said before, the caterpillars are toxic and advertise this fact by having black and orange/yellow warning colours. And it works! This is how we see cinnabar caterpillars – lots of them stripping the ragwort plants bare. So the birds don’t eat them. But in that case why are we not knee deep in cinnabar moths?

Part of the answer is that parasitic wasps will attack them and place egg(s) in or on the caterpillar body and these, after hatching will consume the caterpillar. Sally took this photograph of a female ichneumonid wasp just about to lay eggs – you can just see her short ovipositor being prepared to plunge into the cinnabar’s body. I have no idea of the name of this wasp but it is both beautiful and interesting.

This time last year, Karen gave me some live cinnabar caterpillars from her garden. I can’t remember how the conversation started but I was telling her the same story and I added that somehow some ichneumonid wasp species were able to modify the behaviour of their host caterpillars. Karen told me that some of her cinnabar caterpillars were now climbing up the wall of house – was that normal? Well, not really. They should be leaving the ragwort plants and going down and pupating at soil level – not going up! A few days later I was the proud owner of several inappropriately behaved caterpillars. They all died and from each one  several ichneumonid wasp larvae walked out and formed cocoons in the box. Caterpillars have a small cluster of brain cells and somehow the wasp had modified the action of these cells to their own advantage. Presumably there is some benefit to the wasp to pupate higher up and off the ground.

Almost a year later the wasps started to emerge. I let all but one fly off. I wanted to photograph it under the microscope but I made a real mess of things trying. I ended up with a damaged insect that was too large for the camera sensor. The wasp deserved better. I decided not to use the photograph but receiving Alison’s photograph prompted me to change my mind. It is an ichneumonid wasp (left) but I don’t know the species. But they are just perfect – I really like the wing veins and the antennae on this one. I wonder how many caterpillars this species destroys each year.

Right on cue, Jeff sent me this photograph of  Box Tree Moth caterpillars (below). He introduced us to this invasive and very destructive moth in a previous post. Now he writes –

“Ann and I are now battling with Box Tree Moth [caterpillars] and I’m not helped by the young Robins or others, who seem reluctant to eat the caterpillars, unless they are mixed with digestive biscuits! ”

I have never seen the caterpillar and I was rather surprised by the colours. Apparently the caterpillars are toxic, which is why, like the cinnabar, their numbers can rise so dramatically. But, as Jeff has discovered,  birds can eat them (without ill effects).  Some of Jeff’s caterpillars are now pupating, getting ready to turn into moths. While I was “researching” this post I discovered that only a very few cells from the caterpillar are retained through the change caterpillar – pupa – adult. And the brain cells are one such group. Some biologists are now seriously considering whether a moth could retain some memory of its life as a caterpillar! Although the Box Tree Moth has only been with us for a few years I bet there is already one or more ichneumonids attacking them.

Alison tells me that the ragwort was growing in her garden because she had forgotten to mow the lawn. I am much the same except I have forgotten how to mow the lawn (and no! Sally doesn’t do it either). Karen, I know, has a very wildlife friendly garden and poor Jeff and Ann just don’t seem to have much choice at the moment. There is so much life out there. As for lawns I go with Plantlife’s No Mow campaign.

Thanks to Alison, Jeff and Sally for the photographs. Thanks to Karen for the caterpillars – sorry I have not been able to report to you in person.


 Posted by on 30 August 2020 at 10:05 pm

  One Response to “Caterpillar Brains”

Comments (1)
  1. Fascinating stuff Malcolm and you learn something every day.

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