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Humidity
Once the caterpillars have hatched, they are carefully transferred to another container. Because the tiny caterpillars are very vulnerable, I use a feather or a fine brush for this job. When all caterpillars come out at once, they can be carefully wiped out of the box. If there are still unhatched eggs, caterpillars or eggs have to be removed one by one. The advantage of the smooth surface (no paper on the bottom) will get clear now. Because they are not able to get hold on the surface of the container, it's relatively easy. The young caterpillars are transferred to a petri dish or other small transparent box, ventilation holes are not necessary. Because the small larvae can dehydrate quite quickly, a high humidity is also important. Breathing on the inside of the lid is no longer necessary because the foliage evaporates enough water, take care no condensation is formed on the lid. Young caterpillars of large species such as Atlas moths, often need to drink something or they won't start eating and die after a few days. Sprinkling a few small drops of water on the leaves, ensures that the young caterpillars can drink if necessary. As the young larvae start eating, they get enough moisture through their food and water is more harmful than of help. Cover the bottom of the container with some leaves of a suitable food plant and then put it on a save location. Young caterpillars won't feed immediately after hatching, often takes several hours to two days before they begin to eat. In the meantime they walk around a lot in the box or petri dish. Ensure that sufficient fresh food is available and the box is not too large, so they stay in contact with the foliage most of the time as they walk around.
Disease
The increased humidity will keep the leaves fresh. Change the leaves once every one or two days and clean the container with hot water and some unharmful detergent. The cleaning of the containers is very important because the increased humidity and little ventilation can cause diseases and mould easily. A sick caterpillar is often recognized by the secretion of brown fluids or diarrhoea and does not move or eat Due to the moisture loss it will shrink and die within one or two days. (Don't confuse this 'not moving and eating' behaviour with the big clean-up before pupating.) Remove healthy looking caterpillars as soon as possible and isolate them one by one in separate small containers, that way some may survive. This diarrhoea disease is very contiguous and will infect the other larvae in no time. Good practice to limit the damage beforehand, is to split a large culture into two or three separate containers. Work with clean tools (scissors and shears) and breeding tanks, disinfected with chlorine or other detergent when symptoms of disease are visible.
Moulting
Depending on the species and temperature, there are four to ten days between every moult. Before moulting, the caterpillar will sit still for one or two days and spins an imperceptible net of silk for some extra grip. Try not to disturb the caterpillars to much while cleaning the tank, cut of the piece of leaf or branch they are attached to and take it over to the new tank. Directly after the moulting, the caterpillar will sit still some time to let the external skeleton harden. Usually the larvae have a pale colour just after moulting but during the hardening of the skeleton, this will gradually turn brighter. Often the old skin is eaten to benefit the nutrients left behind, other species leave their skin for what it is. A caterpillar that has been disturbed to much after moulting, will mostly take off without eating its old skin.
Ventilation
After the first moult, the caterpillars go into larger containers. I use it mostly empty cups cottage cheese or plastic transparent boxes playing cards are kept in, these are filled with pieces of branch with leaves. The larvae can be observed through the transparent cover. Depending on the size of the caterpillars, they will need a larger container as they reach second or third instar. There are caterpillars that will show hostile behaviour when they are densely packed, they can hurt each other quite bad. Consider how the butterfly eggs are deposited, if they have been deposited individually or with two or three at once, it is possible they won't get along that well. If ova are deposited in large groups, it is possible they refuse to eat if the larvae are kept single or wander off to far. These larvae will only eat if kept group wise. As larger containers, I use plastic transparent storage boxes with transparent lid. A major advantage is that in comparison with a glass terrarium, they are inexpensive, lightweight, stackable and easy to clean. A ventilation opening is made in the lid by cutting out a rectangle with a Stanley knife, a piece of mesh screen or curtain fabric can be fixed with duct tape before the opening. I use these storage boxes on their side so that the height is greater, that will make it possible to put in branches in a jar or bottle with water so the leaves will stay fresh longer. Evaporation from the leaves provides a higher humidity. Because caterpillars are not the most intelligent animals, the jar or bottle must be kept sealed with plastic wrap and elastic bands. Caterpillars will otherwise crawl down along the twigs until they are under water, the reduced supply of oxygen will make them inactive and they drown. If that happens, it's worth trying to save them by drying them thoroughly with paper towel and keep them on a well ventilated spot for a couple of hours. A caterpillar will die after several hours under water, although they might look dead, they can often be saved. To keep the host plants fresh, I use glass mustard jars with a flexible plastic lid. A few holes are made in the lid so the branches fit in tight, that way they can never reach the water.
The end of the larva stage
As the caterpillars grow, they shed skin a few more times. Depending on the species, this will happen four or five times during their lifecycle. If the larvae are finally ready to pupate, this can often be noticed by the behaviour they exhibit. Suddenly they stop eating and stay put for a while, the intestines are emptied as an often slimy blob of soft stool. From now on the caterpillar will start looking for a suitable place to prepare for pupation. At this stage, they are often very active and begin to walk around the entire stay until they finally found a suitable place. In many cases discolouration of the larvae is visible, head or back turn darker. Caterpillars that make a cocoon of silk are usually quick at finding a suitable location between the branches and leaves. Species that pupate above ground but don't spin a cocoon (butterflies), will find a place on a twig or against the top or the container. The last group includes species that normally pupate underground or in the litter layer. When these caterpillars show discolouration and the typical "run around" behaviour, they are transferred to soil filled cottage cheese cups. Each larva will have its own private cup so it won't be disturbed. If multiple larvae are kept in a large container, they will disturb each other during pupation, resulting in a higher chance of deformed pupae. If soil is used, be sure it is not fertilized soil, the salts of these fertilizers can dehydrate the caterpillars. I use slightly damp leaf mould or seeding soil, also a couple of pieces crumpled kitchen paper can serve as nothing else is available. Make sure the lids are well anchored, do not think a cover is enough to keep them in the container. Especially hawk moth caterpillars have no problem popping of the lids and sneak away quietly. Stack the cups and put a stone on the upper cup, that should do just fine, stack the cups in sequence or brand them with a date, so you can estimate when the caterpillars have turned in to pupae.
Prepupa
Pupae or chrysalis that hang freely, pupate quite quickly. The period between fixation of the larvae and pupation, usually doesn't take longer than a day or two. During this time, the caterpillar becomes noticeably shorter and gets rid of its skin for the last time. Caterpillars that spin a cocoon or pupate underground usually need a period of five to ten days before they turn in to pupae. During this stage the caterpillar shrinks due to evaporation of moisture and will become much shorter, this stage is called prepupa. Disruption of the prepupa can lead to disfigured pupae who eventually die or produce deformed butterflies if they survive and manage to emerge. If I'm not sure how long a species needs to pupate, I will wait digging them out till fourteen days have passed so I'm sure that I will find pupae.
Temperate climate
While the caterpillars grow up, it is wise to keep them under the same climatic conditions in which the larvae live under natural conditions. Breeding native butterflies will give few problems, a well-ventilated container or cage outside and out of the direct sun is generally sufficient. Be sure the ventilation openings or cage are made of a very fine mesh so that parasitic wasp or -flies can't reach the caterpillars. It is also possible to let them grow up directly on the host plant, a fine mesh sleeve over a branch or a plant will keep the flies and wasps out and keeps the larvae on the host plant. Be sure the sleeve is bound tightly at both sides. This generally provides the least work because the leaves on the living branches will not wither and food doesn't need to be refreshed. Inspect the branches before they get sleeved, spiders, ants and ladybug(larvae) can destroy a breed in a couple of days. Removing the droppings out of the sleeve twice a week is enough. If there is a large amount of droppings on the ground, plants will create antibodies, it's best to remove all droppings and not let them fall on the ground while shaking them out the sleeve. Move the sleeve and larvae before all leaves have gone, eaten bare branches recover much slower than branches that still have a fair amount of leaves.
(sub)tropic climate
While breeding (sub) tropical lepidopterans, we have to provide circumstances a good summer month might be able to approach. Beyond one or two warm summer months, it's not possible to breed these species outdoors. Because these species don't hibernate, breeding of (sub)tropical lepidopterans can be done throughout the year if we can find a place indoors. Especially during the winter months, the problem is that central heating causes a low air humidity.
Climate closet
To provide the larvae better climatic conditions and because I often breed several species at a time, I have made a closet in my attic with a size of 150x100x70 cm. The inside is insulated with 10 cm thick polystyrene foam board. This cabinet is lit daily during 14 hours with two 4 Watt 12 Volt led lamps, because of the low voltage, moisture is no problem. The lamps provide more than sufficient light. The combination of lamp and transformer unit, heats the closet to a temperature of 25 to 30 °C, this depends on the temperature outside the enclosure. To keep the temperature reasonably stable during night, two limestone stone tiles with a size of 50x50x5 cm are placed at the bottom of the closet. These smooth tiles are easy to clean and absorb warmth when the lights are on, during the dark period they release the warmth slowly. A mesh covered bucket of water is placed in a corner of the closet to maintain a high air humidity. Above the bucket, a fan from an old computer case takes care of air movement, the fan is connected to the transformer of the lamp as well. This combination makes it possible to create tropical conditions with a humidity between 75% and 90%. At this high humidity, spraying the leaves is unnecessary and diseases are therefore much less likely to develop. Ventilation of the compartment takes place through two adjustable vents in the doors. The combination of ventilation, air movement and isolation ensures that despite the high humidity, no condensation occurs. Eggs, caterpillars, pupae and cocoons can be kept in well ventilated containers or cages when placed in this climate closet. Tropical and subtropical species develop rapidly and do dehydrate, make sure to clean the containers daily because these are ideal conditions for mould as well.