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!
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!
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:
- Quarantaine: seperate larvae in smaller groups, or individually, in multiple containers/enclosures, to prevent further infection, and to keep uninfected larvae safe from pathogens.
- Desinfection: viruses and bacteria in particular, can linger and survive within rearing containers and enclosures for a long time. A good idea to to boil rearing equipment in hot water, desinfect with ~90% alcohol solutions, or get new equipment altogether.
- 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. Signs of infection in larvae are as follows: vomiting, liquid feces, restlessness and pointless wandering, discolouration (being more pale or darker), smelling rotten/fishy, leaking body fluid, weakness (clinging/hanging unto objects)
- Changing the source of the host plant may have positive effect: pesticides can also be a source of illness, as can BT-bacteria that are also present in nature and sometimes used as insecticide.
- Lowering the humidity helps reduce growth of fungi and bacteria in rearing enclosures
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).
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 months and then be gradually warmed up to room temperature to trigger hatching.
Larvae: 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.