Larvae moving poo about

[chrisox]

I observed a 1st or possibly 2nd instar Brimstone larvae on a Buckthorn leaf picking up bits of it's poo in it's mouth and moving them to other parts of the leaf (or possibly trying to drop them over the edge). It seemed to do this with a number of pieces. Has anyone else observed this behaviour and know if it has any meaning?

Chris

[Sij]

Hi I have seen this in a butterfly species, but cannot remember which one! Think it was one of the fritillaries.Sorry i can't be of greater help ha ha

[Vince Massimo]

Hi Chris and welcome to UK Butterflies.

I have studied Brimstone larvae, so will have a go at this, although hope that some others may chip in.

Firstly, I have to say that a larva's association with its poo (frass) seems to be complicted and confusing (at least to me). I have observed Brimstone larvae moving frass to the side of the leaf when they happen to encounter it. I have looked at all of my larval photos and there are a few where frass has accumulated on the side of the leaf, but only with early instars.

Brimstone larva 2nd instar

This may be because the early instars feed primarily in the middle of the leaf and so move the frass out of the way to the leaf edges. Later instars feed on the outer edges of the leaf, so their frass might therefore naturally fall away as they feed. This may explain why I could not find any photos of later instar larvae with frass on their leaves.

It seems that there have been various studies as to what larvae do with their frass and why. It's only logical to believe that frass and food should not mix. It could be accidentally injested and, if diluted by water, could potentially contaminate the foodsource. However studies have shown that insect parasitoids and other preditors of larvae use odours or visual cues associated with frass to locate their hosts, so this is another good reason why frass should be removed. Merely dropping it onto the ground results in it accumulating around the base of the foodplant, which apparently attracts ants and encourages them to climb the plant looking for the larva. Some species of larvae (like Dingy Skipper) have overcome this issue by expelling frass pellets at great velocity away from the plant using specialised anal structures.

So far this is all logical to me, but there are many other examples of larva who live amongst their frass, where further study is required to explain the advantages. I can just about cope with the argument that species like Large White, Peacock and Small Tortoiseshell, which live and feed communally and produce a lot of frass, could otherwise be at a disadvantage but benefit from group defences (safety in numbers or lots of protective silk).

Small Tortoiseshell larvae 3rd instar

But then there are species of lone larvae, like Red Admiral and Painted Lady, which live in tents or shelters which are full of frass, apparently without significant disadvantage.

Painted Lady larva 3rd instar

And then there's the White Admiral larva which stores its frass in a purpose-built latrine on its feeding leaf and uses frass as part of a defensive structure. More extreme examples come from tropical regions where some larvae cover their bodies in their own frass as a defence.

Lots of stuff to get you head around and subjects for further study.

Vince

[Padfield]

Interesting!

Two photos from a miserable, grey day in 2017, as my contribution to the exciting, new science of lepidocoprology:





It's difficult to imagine it got the frass on its back accidentally (unless it came from one of the other cats on the same plant).

Guy

[chrisox]

Thanks for the replies and welcome. Yes, it seemed to me it was moving the frass around in a deliberate manor to clear the leave. I watched it for a few minutes and it did seem like a 'tidying up'. Later I noticed it was eating the edge of the leaf the otherside of where it had moved the frass. What you say Vince about health and protection reasons for this does make sense. I have seen other caterpillars pick frass up in their mouths and move it to one side, but it was a long time ago and I can't remember which species, but not Brimstones, although I've never seen something quite as organized as this seemed to be.

Cheers

Chris

[chrisox]

A bit dark, but caught one of my Brimstone caterpillars doing it's rearing up thing (Or is it just trying to look out of the window )