Very Unusual Yellow Caterpillar - Dorset

[dgreves]

But why would parasitisation by a wasp explain the behaviour of the ants? And what would explain the big difference in pattern and colouration?

[Dave McCormick]

I am not quite sure, but if the cat was exposed in the open near an ant nest, I suppose the ants might see it as prey and attack it? All I can think of. Someone else also thoguht it was a odd powdered quaker caterpillar.

[Trev Sawyer]

If the caterpillar was "sick" ie parasitised, it may well produce chemicals which suggest to an ant that it is dying (and therefore becoming a potential meal). Once the ants detect these, the message would spread and other ants might join in. Alternatively, the chemicals exuded might for some reason be sweet(?) and attract the ants that way.

Trev

[dgreves]

Ian at ukmoths very kindly got back to me yesterday with a suggestion from Roy at ukleps that it might be Black Rustic final instar in an unusual yellow or sick form. He says "Build very similar. Also note the dark marks either side of the spiracles on the first two or three abdominal segments - these match too".

[Dave McCormick]

Would explain why it was in open, right area if it feeds on low growing plants, including heather. Looks good too, here is an image of the black rustic cat: http://www.habitas.org.uk/moths/larva.asp?item=6325

[dgreves]

Yes - that looks similar to the image Roy attached to his email.

No heather along this bit of the coast but downland seems to match the habitat conditions also.

I think we may have a winner!

I'm surprised parasitisation would provide such an obvious clue to potential predators - I assume the parasite would perish along with the host if it was consumed. There are dozens of ant hills in this valley - they dot the landscape quite dramatically - but I rarely see the ants themselves above ground. Adonis Blues also a frequent sight here and I believe they have a relationship with the ants too.

I just found a video of ants attending to Adonis Blue larva:

http://www.arkive.org/adonis-blue/lysan ... eo-09.html

and they seem to cluster around the rear end much in the same way as shown in my video clip - I wonder if they confused it for a different species.

[Dave McCormick]

Adonis blue caterpillars, like several other blues (large and alcon blues), make a sound quite like that of that of a ant grub. The ants find the cats, thinking they are their grubs because of this and take them back to their nest where they can be looked after and reletivly (not totally though) safe from predators. They are fed and cared for like the ants grubs too. The cats pupate in the ant nest and emerge as adults, crawl out of the nest, expand wings and fly away,

This black rustic cat doesn't do that, not many in UK do that besides some blue butterfly species, so might be attacked if showing weak signs or smells, signals etc...

[dgreves]

I went back to the same spot yesterday and no sign of caterpillars (or moths) but I did find thousands of Braconidae wasp eggs newly fastened to many of the same grass stems:



Is it possible they were responsible for parasitising the caterpillar do you think?

[Dave McCormick]

Actually those are brachnoid cocoons (those that parasite large whites have yellow cocoons), the eggs are laid in caterpillars, the grubs feed inside the caterpillar and eat some of what the cat eats and when the cat goes to pupate the grubs burst out and create those cocoons so I'd say they could have parasited the caterpillar.

[dgreves]

Today I found them tucking in to a Burnet Moth caterpillar:



Further along the coast another insect was evening the score:

[Cotswold Cockney]

Today I found them tucking in to a Burnet Moth caterpillar:



Further along the coast another insect was evening the score:

That lower picture is truly remarkable.
.

[dgreves]

I thought it was an ant at first but it didn't look right on closer inspection. Someone tells me it's another wasp - but a wasp with no wings? Is this an early developmental stage? And could it be the same species as emerged from the cocoons or a different one?

[dgreves]

Fascinating article on New Scientist about "Zombie Caterpillars":

http://www.newscientist.com/article/dn1 ... wasps.html

It goes on to say:

"One parasite, for instance, infects an ant and appears to "convince" it to climb to the tops of blades of grass where it is more likely to be eaten by grazing sheep - which the parasite needs to get into in order to complete its life cycle."

If this had been the case with the original yellow caterpillar my remark about being munched next day by the cattle might have been apt!

[Dave McCormick]

Today I found them tucking in to a Burnet Moth caterpillar:

Actually I think they emerge from the cat and pupate, they have finisehd with it, thats what the white things are, they spin cocoons besdie the body of the caterpillar. I was rearing some moths recently from caterpillars I found at a lake near here, 10 adults emerged, but also 4 wasps, the grub 9white) burst out of the caterpillar when it was fully grown and pupated beside it.

The second image looks like it could be a velvet ant. Velvet ants are not ants, but infact wingless wasps that inhabit moores and other grassy places.