Caterpillars, eggs, adults (care info!)

Taking care of caterpillars, eggs and adults are seperate skills that have to be mastered in this hobby. This page with information hopes to provide enough information regarding all these stages, and how they should be treated and taken care of! When somebody talks of “breeding moths”, they’re actually referring to the art of taking care of caterpillars! Pupae take virtually no care and adults are often short lived. The truth is that the core of this hobby is taking care of larvae!

PART 1: CATERPILLARS

CaterpillarsA colourful selection of larvae

When taking care of caterpillars, the first and most important thing is to learn how this species survives in the wild, and to emulate these circumstances in captivity. Generally, important factors in keeping larvae healthy are: hygiëne, host plant, humidity and ventilation. I will elaborate on these factors below here!

Generally speaking, caterpillars are the most senstive stage in captivity. Lepidoptera are typically monophagous and specialists on certain kinds of plants; this means caterpillars will rather starve than try to feed on a plant they are not familiar with. Thus, the correct species of host plants are required. Even the very polyphagous species of moths and butterflies will not feed on any random plant though they may feed on a wide range of commonly available plants; one still has to study the biology and ecology of the species well. As the majority of species seem to be specialise on certain families of plants instead of single species however, alternatives to the natural host plants can be found in captivity. A moth or butterfly that feeds on highly specific species of Fabaceae in the tropics may just accept common clover (Trifolium) or Robinia in captivity. Thus, experimentation is quite worthwhile.

Hygiëne: caterpillars are very prone to infection. Both bacteria, fungi and viruses are pathogens that may cause high mortalities in caterpillars in captivity. This is because often the density the caterpillars are being kept in are unnaturally high in captivity (compared to in the wild, where solitary species often keep their distance from eachother, whereas in captivity many can be held in a container) and also because they are exposed to different pathogens and bacteria, like their own feces (in nature, these fall to the ground while in captivity, they accumulate in their own container). Caterpillars, and insects in general, do not have an advanced immune system, and are prone to infections from such pathogens. There are also many pathogens to be found in the wild, like Bacillus thuringiensis and (Baculo)viruses like NPV (Nuclear polyhedrosis virus) that affect Lepidoptera, which may accidently be introduced via host plant in the wild.

The most obvious and effective way to reduce pathogens is hygiëne: remove feces every 1-2 days from the containers, and often include fresh host plant with fresh leaves to avoid mold from growing. Containers should be wiped with cloth periodically. If the worst case scenario happens and larvae do get sick for some reason (it can happen randomly): if the infection is viral or bacterial, chances are that it may cause a very high mortality rate amoung the larvae, for such infections are highly contagious. However, to prevent the virus from killing the whole bloodline, one can take measures such as:

How to stop caterpillar viruses and diseases in captivity?

Quarantaine: seperate larvae in smaller groups, or individually, in multiple containers/enclosures, to prevent further infection, and to keep uninfected larvae safe from pathogens. Obviously, containers must be airtight for this to work, so that no bacterial spores or viral particles can contaminate other caterpillars through the air. Raising groups of the same species in seperate rooms and containers can help.
Desinfection: viruses and bacteria in particular, can linger and survive within rearing containers and enclosures for a long time. A container in which sick larvae have died, can potentially infect healthy larvae months or years later. A good idea to to boil rearing equipment in hot water, desinfect with ~90% alcohol solutions, freezing equipment for a long time (-20 to -40C) or get new equipment altogether. This will get rid of most harmful micro-organisms.
Preventive destruction: often, larvae that exihibit signs of infection, have a very low survival rate while posing a risk of infection to the healthy ones. If one doesn’t have moral issues with this, it is a good idea to preventively kill livestock that makes an impression of being infected. Common signs of infection in larvae are as follows: vomiting, liquid feces (diarrea), restlessness and pointless wandering while having no interest in food, discolouration (being too dark or too bright), smelling rotten/fishy, ‘sweating’ aka appearing wet and leaking body fluid, weakness (clinging/hanging unto objects), anal prolapse, black necrotic spots on the skin. Especially, if you succesfully want to raise sensitive and hard to raise species, one must be relentless against them. Nobody likes killing their own ‘pets’, but chances of survival of sick larvae are almost 0%. Once infected, they will die a slow death while only spreading the disease to other individuals. Killing a few caterpillars means you can save many others from becoming sick. Destroy infected caterpillars preferably by freezing them to death. Otherwise, you can be creative, but please resist the temptation of crushing them to death in the cage or container that also has healthy caterpillars; in many cases, their body fluid carries the disease, and splattering their guts everywhere can make the virus airborne and spread it to new individuals, or infect them when they touch the body fluid.
Change the food: Host plants can also commonly be a source of illness. This can happen in several ways. One of these ways is pesticides. Especially in agricultural areas, farmers may spray with chemicals (insecticides) that are specifically harmful to insects. This may coat all the plants in the general area of the spray zone with insecticide that can remain for a long time. In some cases, the wind will play a role, and carry the toxic vapour away from the spray zone, and spread it over plants quite far away. Avoid using host plants that grow directly next to orchards or agricultural fields. Commercial plants such as food crops are commonly treated with insecticide. In particular, Bacillus thuringiensis, a bacteria that specifically targets and kills caterpillars, will affect moth breeders. A solution with these bacteria can be sprayed over farmland to destroy Lepidopterous pests, but these bacteria and their spores are known to disperse with the wind quite well, causing a drift-off that may make many plants in the area harmful to caterpillars. Secondly, host plants can be coated in toxic exhaust fumes – do not pick plants that grow next to busy roads. Thirdly, many natural enemies of caterpillars will hide on their food plants, and wait to be ingested. Some parasites lay eggs on host plant leaves, and infect caterpillars that eat them. Bacterial spores and viruses are also present in host plants, since other (wild) caterpillars can also spread them in the foliage. Last but not least, plants themselves can also carry their own, natural diseases such as fungi – that will attack the plant, not the insect. A plant disease cannot infect an insect, but sick plants make for low quality food. Ingesting mold-covered leaf or necrotic tissue may be harmful to their health. Would you eat meat from a sick cow, or eat moldy vegetables? Exactly.
Increase the hygiëne: Caterpillars are often extremely sensitive to hygiëne. That is because in rearing containers, they live in their own filth, and often in high numbers. In the wild, this is very rare. Old caterpillar poop can develop mold and fungal spores that are harmful to caterpillars. When a caterpillar dies, its carcass can contain diseases or develop a culture of harmful micro-organisms. Keep the food plants fresh, and remove excrements and dead individuals from the container regulary. If you rear caterpillars by keeping a cut food plant in a water bottle, change the water often; the water easily becomes rotten and will become a harmful, smelly soup. This is absorbed by the plant and consumed by the caterpillars. Change the bottle every week if you can (here is your excuse to drink more wine!).
Decrease the humidity: Micro-organisms love two things: warmth, and humidity. Sadly, not many insects appreciate a cold environment, and raising most of them in low temperatures is no option. But we can control the humidity. You will hear the word “ventilation” a lot on this website. Airtight plastic containers can become a death-trap for caterpillars, and brooding chamber for micro organisms. Try to ventilate your caterpillars. Use cages and rearing sleeves. Change the lid with netting. Don’t spray your caterpillars with water every day and feed them wet leaves. Prevent condensation and moisture in the rearing container. You can create a substrate of paper towels in plastic containers that will absorb moisure. Too wet and too humid is an invitation for diseases.

Picture: the terrible effects of nuclear polyhedrosis virus on Acherontia atropos.

Host plant: when keeping insects, or pets of any kind, food is generally always an important factor. However, butterflies and moths are specialists that often only feed upon a single family or species of plant. Important is that the host plant is healthy and in good condition. Try to avoid feeding desiccated or sick looking leaves. Also important is the source and location: some host plants may be contaminated. For example, picking host plants along busy roads is not a good idea, for they are often covered in exhaust fumes. Also beware of insecticides/pesticides: especially with plants from garden centres, flower shops or plants picked along plantages, especially fruit tree plantages. Agricultural crops are often sprayed by harmful chemicals that may disperse with the wind unto plants in the near vincinity of these plantages. Always strive to keep host plant fresh, caterpillars should be given fresh food every 2-3 days, or otherwise reared on the live plant.

Humidity and ventilation: Humidity plays an important role in the overall health of the larva. Too much humidity will support the growth of parthogens like fungi and bacteria in the larval rearing containers, which can be dangerous for their health. Not enough humidity causes other problems like death/losses from failed molts (larvae rely on humidity to slide out of their old skin when shedding, if the air is too dry they will dry up inside their old skin and get stuck) – and also dessication in general. Overall, there is no perfect humidity to rear larvae in – it varies greatly per species. As you can imagine, species from tropical rainforests or high cloudy mountains will require a lot of humidity, while others will not be able to tolerate even the slightest humidity, mostly species from desert or rocky island habitats. Ventilation plays an important role in regulating said humidity. However, it is also a seperate factor. Some species require air flow, and will become ill in airtight containers, regardless of the required level of humidity for these species. (A good example is larvae of Papilionidae, that often die swiftly if reared in jars with no ventilation or air flow, even if provided the correct level of humidity).

PART 2: EGGS

Eggs: Lepidoptera eggs, though diverse in shapes and appearances, should be one of the easiest stages in captivity (though there are exceptions.) When fertile, they should be ready to hatch on room temperature, the main exception being species that overwinter as eggs. These species need to be kept cold for serveral month s and then be gradually warmed up to room temperature to trigger hatching. Eggs can be overwintered outside in a plastic tube inside a thick envelope with bubble wrapping or in a fridge, in a slightly humid well isolated container.

PART 3: IMAGOES

Adults: The adult biology of several moth (and butterfly) families is quite different. To generalise what sort of care they need is difficult. For example: some of them have no functioning mouth and will therefore “starve” (run out of energy in 3 to 15 days). Some examples: Saturniidae, Lasiocampidae. Other moths will be able to feed as adults and may have a longer lifespan – from 1 to 6 months if well fed. Examples are Sphingidae, Noctuidae,Erebinae such as Catocala, but also almost all butterfly species (for example Nymphalidae, Papilionidae) are able to feed. This means that some will need to be fed. All Lepidoptera feed on sugary solutions. However in the wild some species prefer flower nectar, others rotten fruit (fructivorous), mildew, tree sap and more. A good substitute for this could be a solution of honey and water (50/50). Flower feeding species will be attracted to hummingbird feedings or actual flowering plants and could be provided those in captivity. Fructivorous moths prefer rotten fruits such as fermenting banana or strawberries. All butterflies and moths can also be semi-forcefully fed by hand by unrolling their proboscis into sweet mixtures – some species will not feed independently in captivity and need to be forced.

Are you interested in a video tutorial by me? Then click the link below, and make sure to watch parts 1, 2 and 3!

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Citations: Coppens, B. (2019); Written by Bart Coppens; based on a real life breeding experience [for citations in literature and publications]

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