When rearing caterpillars in plastic boxes there are some additional warnings:

  • Don't cram boxes with foodplant since this can cause caterpillars to be crushed when the lid is replaced.


  • Try not to use leaves taken from busy roadsides as these may be contaminated by an oily film which could kill caterpillars. If roadside collection is the only option avoid dirty older leaves which are growing low down and wash the leaves in tepid water to remove any oil film.


  • Don't put wet foodplant into an airtight container; dry it first to prevent excessive condensation forming.


  • Don't dislodge caterpillars from the old foodplant when cleaning out as the may be undergoing the delicate process of changing their skins known as moulting or ecdysis. Always cut around them and discard the remaining material. Caterpillars should not be handled as squeezing can damage internal organs and perspiration may burn their delicate skin. Furry caterpillars on the other hand can cause irritation to human skin!


Experience has shown that some species rarely do well in plastic boxes even as small caterpillars. These include: Robin Moth, Cherry Moth, Emperor Moth and Tau Emperor.

Netted Cages 

Netted cages come in a variety of sizes but tall cages which are narrower from front to back than their width are favoured since they will sit on shelves and provide enough height to hold potted foodplants. Netted cages can also be used for butterfly /moth emergence, pairing and egg laying. When purchasing one you should check that it has been made with a good quality nylon mesh which will not rot if it gets wet. The mesh should also be very fine and the door close fitting so that predators such as wasps and spiders are kept out. High quality netted cages are usually available for sale  on our sales stand. Unlike plastic boxes netted cages can be kept in direct sunshine and this is beneficial to most caterpillars. Direct sunshine kills viruses and bacteria and the ventilation provided by the netting lowers humidity which reduces the spread of any infection.

The netted cage can accommodate the pupation requirements of caterpillars which hang from the roof, attach themselves to the foodplant or (if a tray of damp peat is provided those that pupate amongst surface litter or underground). If rearing a lot of caterpillars however it is usually best to separate large caterpillars as otherwise once pupation begins they may be disturbed by those that are still feeding or wandering in search of a suitable pupation site. Another point to bear in mind is that for caterpillars pupating at or below the surface the droppings known as frass will quickly contaminate the damp peat, producing moulds and fungi which can lead to disease and malformed pupae. One simple tip to reduce mould and fungal development is to sprinkle the surface of the peat with a few grains of ordinary rock salt or table salt! However this should not be used as a substitute for maintaining good hygiene. When silkmoth caterpillars are getting ready to pupate many species will spin cocoons in the corner of he cage which can be a nuisance as they are difficult to remove without damaging the pupa inside. Some caterpillars may be even less considerate and spin a cocoon between the cage and the door preventing it being opened! The simplest way to avoid these pupation problems is to remove caterpillars which are ready to pupate to alternative quarters such as ice cream tubs. Experience will enable the breeder to know when a caterpillar is ready to pupate. Generally the signs to look for are discolouration (normally becoming darker) shrinkage, a firmer looking appearance, excessive wandering and no interest in feeding.       

There are two ways of feeding caterpillars in netted cages. The first is with potted plants which is excellent if plenty of food is available and the second with cut food stood in bottles of water, oasis (used by florists) or wet sand.

If using potted foodplants beware of plants bought from nurseries and garden centres as such plants may have been sprayed with chemicals or treated with long lasting systemic insecticides. If the caterpillars are less than about one and a half inches in length we usually soak the plant in a dustbin of water overnight as many predators such as spiders earwigs, ants and beetles hide amongst the plant roots during the day and will come out at night to hunt the caterpillars. 

It is not always practical to use potted foodplant as most plants are simply too big and many species of moth feed on trees. When using cut foodplant in a netted cage a number of considerations should be borne in mind:

The temptation is always to leave the caterpillars on cut foodplant until they have eaten all or most of this. This is fine if this occurs within 48 hours but after this many plants will start losing their nutritional value and their cut stems begin to breakdown polluting the water which they then reabsorb. This leads to dietary disorders that weakens the caterpillars and predisposes them to disease. Anyone who has kept cut fennel in a jar of water for too long will know how putrid the water can smell! Pots of wet sand may appear to be better as the breakdown of soft stems is slower however the pots are more likely to become contaminated with frass (caterpillar droppings) and will become polluted within a few days. It is also possible for caterpillars to suffer from overhydration therefore pots of wet sand are preferable for cut plants of conifers such as pine that are naturally on the dryish side and would become over hydrated in bottles of water. In addition some plants that naturally contain a lot of flui such as nettles, spurge, milkweed etc. easily become over hydrated and are best fed as potted plants or if only cut food is available, in moist sand. Of course when caterpillars get really large cut food may be eaten before it has a chance to wilt dispensing with any need to place the stems in moisture. Be wary of some plants that look fresh even after a few days but are not. For example sallow (goat willow) and poplar kept in water looks fine after several days but if touched it feels dry and crispy and is obviously not very appetising to the caterpillars.

The other main consideration regarding cut food is preventing the caterpillars drowning in the water. Caterpillars can be notoriously stupid and will squeeze their way down between a stem and a bottle and carry on walking down the submerged stem until they eventually drown if not spotted at an  early stage. Plugging the jar or bottle with cotton wool or other inert material will stop this and also prevents fouling by the frass and evaporation losses. We tend to use narrow necked clear plastic or glass bottles (i.e. milk bottles) as the level of water can be observed and topped up if necessary (when changing the food it is best to change the water completely). In sunshine the water heats up quickly so very narrow bottles are usually unsuitable. 

There are a number of other methods for rearing caterpillars and one of the most popular alternatives is known as sleeving. This involves rearing the caterpillars on a growing shrub or tree "sleeved" within a net bag tied at one or both ends with draw strings. Additional information on this method and rearing caterpillars generally can be found in the following recommended books. 

Breeding Butterflies and Moths
By Ekkehard Friedrick, Edited by Maitland Emmett
Harley Books 1986

Butterfly Culture
By John Stone and H.J. Midwinter
Blandford Press 1975

The Silkmoth Rearers Handbook
By Brian Gardiner
The Amateur Entomologist Volume 12, 1982

A Lepidopterists Handbook
By R Dickson
Amateur Entomologist Society 1976

Breeding The British Butterflies FINAL PAGE