www.ukbutterflies.co.uk

Hi,

First off, I know caterpillars shouldn't really be kept indoors, they should be left outside on their natural foodplant. But these particular caterpillars (Small Cabbage Whites) were on my mother's cabbages and the choice was between me keeping them indoors or her killing them - either way, they weren't staying on her cabbages.

I have been feeding them every day and they have grown really fast, and 5 of the biggest ones have now turned brown and are much more active. I read on the internet that this colour change probably means they are ready to pupate, so I moved these to a separate, taller container just for them and put some twigs in it as well as some leaves at the bottom in case they still need to feed up a little.

However, the internet also informed me that the caterpillar stage generally lasts 2 weeks and this particular species grows to about 3.5cm before pupating. Mine however have been caterpillars for almost a month now, definitely more than 3 weeks, and are easily 5cm. And they are still eating, HUGE amounts now thanks to their size.

I just don't understand why they haven't pupated yet, when they seem otherwise very healthy and fat. They crawl up the sticks and down again, but never look like they are even preparing to become a chrysalis. I used to keep these caterpillars as pets all the time when I was a child and I don't remember it being this much work

Any suggestions greatly appreciated!

Hi Rosana,

Any chance of a photograph of the larvae? Small White caterpillars do not usually become brown in colour prior to pupation and I wonder if they may be a different species.

Felix.

I think the brown larvae are moths. This happened to me when I was younger too! They may probably be the Cabbage Moth (Mamestra brassicae). They are very common on Cabbages in the summer. The larvae grow up to 45-50mm & the body can be various shades of green or brown with a dark edged thin pale dorsal line, a dark dorsal marking on the slightly humped 11th segment and a broad pale spiracular line; head usually light brown and spiracles white, edged with black. It feeds on various wild & cultivated plants, especially those of the cabbage family. The species is double or sometimes treble-brooded with the larvae having been recorded almost every month of the year but usually during the summer months.
The above information is extracted from the book " The colour identification guide to the caterpillars of the British Islles" by Jim Porter:1997 Viking Books.
Hope this helps, but keep rearing them and you will get a nice suprise when the hatch from their cocoons!
Lee (Cornwall).

Hi Rosana,

I am not an expert on moths, but my books say that Cabbage Moth larva pupate underground. You may therefore need to incorporate two inches of light soil or compost in the bottom of their container, which may encourage them to proceed to the next stage. If you want to release some or all of them, they will feed on the leaves of almost any wild or cultivated herbaceous plant and have also been found on Sallows (broad-leaved Willow) and Oaks.

Vince

I am pretty certain they are butterflies - the caterpillars started out translucent green, and very tiny, then turned a more opaque green and finally brown when they reached about 3cm. The eggs were pale yellow and laid singly on the underside of leaves. I will try adding a few inches of soil to the container in case they are moths anyway. Will try and take pictures of some of the caterpillars which are at different stages as well as the ones that have turned brown.

Both the brown and the younger green caterpillars have a pale green-yellow line along either side of their body but no stripe down their back. They also have no humped segment.

I take it back, they are moths. I looked the moth up online and found this photo that looks exactly like the big caterpillars I have: http://ukmoths.org.uk/images/hires/2154 ... arvaDG.jpg

I was convinced it was the butterfly because when I looked up small cabbage whites the photos looked like the green caterpillar stage which is why I was confused when they suddenly started turning brown overnight...So I just need to add a couple of inches of soil for them? Also, should the soil be dry or still have some moisture in it? If I keep the pupae to hatch them will I have to spray the soil once in a while or anything?

Thanks for all your help

Hi Rosana,

Unless you get an authoritive view on this, the logical course of action would be to imitate natural conditions. Try using slightly moist soil or compost and do not allow it to completly dry out. A few days after some of the larva have pupated, I would be tempted to move them into another storage container with moist soil to avoid them being damaged by other larva when they start to seek their own own pupation sites. Hope this helps but, I would point out again that I am not an expert on this species.

Vince

Thank you everyone for your help

I put some moist compost into the bottom of the container today and as soon as I put the caterpillars in they all burrowed down immediately. I now feel sorry for the moths I kept as a child that were forced to pupate in the bottom of a glass jar! I will be keeping them in the soil until they hatch, in the garage where it will be cool during winter, and I'll make sure the soil stays a little moist so they don't dry out.

rosana_ wrote: I put some moist compost into the bottom of the container today and as soon as I put the caterpillars in they all burrowed down immediately.

That's a relief, but keep a close eye on them over the next few weeks in case they decide to hatch this season.

Vince (who is not an expert on moths)

This may be helpful if you decide to rear moth caterpillars in the future:
For species which burrow you don't need to use soil or compost. A margarine tub with torn up tissue paper will suffice. Eventually the caterpillar will stop wandering and start to make a loose cocoon with the tissue. Doing it this way makes it easier to observe them afterwards and may be lucky enough to see the actual pupation (I seen this a few times when rearing hawk moths).