Caring for Eggs & Caterpillars

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Monarch butterfly larvae

Caterpillars of Danaus plexippus approaching maturity.

Eggs

Upon receiving your eggs or caterpillars, they will need to be placed into a suitable environment. Very simply, a plastic tupperware container or ‘takeaway tub’ with some tissue paper at the bottom is ideal for most species - this is because it maintains temperature and humidity at a stable level. If this is not provided, eggs or caterpillars may die.

Do not add water or heat to your eggs/caterpillars. Adding water is likely to drown the developing caterpillar before it manages to hatch - a very common mistake. Keeping the hatchlings in a plastic container ensures they do not dehydrate, and once they start eating leaves, the caterpillars should be getting enough moisture from their diet.

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A young Atlas moth caterpillar

This young caterpillar is still at a stage where box rearing is appropriate; once it gains size and sheds to the third instar it will be moved to net enclosures.

Caterpillars

You will need supply of host plant material, each species of butterfly or moth has its own. In many instances the caterpillars may accept multiple hosts, but others will only feed on a single kind of plant. It is often easiest to find some hosts growing locally so that you can access these as required for feeding, e.g. in parks or public spaces, but you can also buy plants from garden centres or online to use for rearing, or to grow on for future breeding seasons.

Rearing caterpillars is not difficult and most caterpillars will pupate within around a month, though some species take longer. You can continue rearing larvae in plastic containers, providing them with bigger ones as they grow, however by the third or fourth stage they will often do better in a mesh enclosure - net rearing tends to be better due to improved air flow as it prevents mould outbreaks and reduces potential spread of disease between larvae.

To keep your host plant leaves fresh, it is a good idea to stand some host plant stems in water. Some plants and trees last surprisingly long, like Liquidambar which can last weeks, although others have a shorter 'shelf-life.' If there are holes between the stems where larvae may fall into the water, you can fill these with cotton wool, tissue paper, or similar.

A wide variety of caterpillars is illustrated at the end of this article - a selection of our favourites from the last few years!

Mature atlas caterpillars

These larvae are around 5 weeks old and nearly finished feeding. After around another week of eating, they will create a silk pad attached to a leaf and spin a silken cocoon within which they pupate. The cocoons are tough, allowing the pupa to remain unharmed within for months if required.

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Luna moth caterpillar & pre-pupa

The two caterpillars in the photo are both Actias luna, however the top one has finished feeding and changed colour to red-brown, indicating it is in the pre-pupal stage and will begin constructing a silk cocoon.

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Pupation

Many species will change colour when mature, indicating they are ready to pupate. The way you treat your caterpillar at pupation should depend on what species you are rearing.

All butterfly caterpillars pupate in the same manner: First, they attach themselves to a surface, e.g. their host plant stems or enclosure sides, by spinning a silk pad. The caterpillar then suspends itself from the silk pad by its hind feet, hanging in a J shape. It may remain in this position for a few days, so do not be concerned by this. When it is ready, the caterpillar sheds its skin a final time, revealing the chrysalis (also called a pupa). The chrysalis will initially be very soft, at which point it is most vulnerable to damage, so do not attempt to move it for at least two days whilst it hardens. If your rearing enclosure is suitable, you can leave the pupae in situ to emerge, or you may wish to remove them to incubate such as in the methods described here.

When it comes to moths, it is important to know whether your caterpillars will burrow or spin a cocoon to pupating. For burrowing species, a large container either with sterile compost at a depth of 10cm, or with tissue or sawdust. We typically use tissue and paper for most burrowing species as it is clean and simple. After about two weeks, you can carefully dig up the pupae and incubate or store as appropriate for that species. For larvae that spin cocoons to pupate within, you do not need to do anything other than ensure their food is fresh until they start to construct cocoons, at which point leave them to complete this process. After about two weeks, you can remove the cocoons from where they are constructed to incubate or store elsewhere.