Lepidoptera larval stages are called caterpillars. They hatch from the egg laid by the adult and develop into a pupae, that undergoes metamorphosis. The word larvae, not neanidae or others, is used because Lepidoptera are holometabolous insects. Such insects undergo a complete metamorphosis: the juvenile stages is really different from the adult (ex. caterpillar and butterfly), presenting different structures and different overall morphology. In hemimetabola, as Phasmatidae, the juvenile stage appears like an immature adult.
In this website, and elsewhere, the larval stages will be called L1 (larval stage N°1), L2, L3… ecc. according to their progression. When the caterpillar hatches from the egg it is called L1.
The larval period is part of holometabolous insect post-embryonic development. In this phase the animal’s life is committed to eat! Caterpillars need to grow a lot, they actually increase their size of various orders of magnitude during their larval lifes, reaching the critical weight that allows them to pupate (reviewed in details in BA Edgar, 2006). To sustain this impressive size increase, caterpillars pass through several larval instars, usually 5.
Attacus lorquinii L1 caterpillar, observed with a stereomicroscope
During growth, larvae store a lot of energy, allowing metamorphosis to take place. The size of the adult is determined by the size of the caterpillar at the end of its larval growth. Although several Lepidoptera species are able to eat during their adult life, this is not increasing their size.
Caterpillar breeding represents the funniest part in Lepidoptera breeding. A general rule is: less you interfere with them, better they will do. Observation is the best way to interact with them.
When you receive the eggs, store them in a small plastic container, allowing little aeration. Petri dishes are perfect to this purpose.
Many species eat their own eggshell upon hatching, thus don’t remove them before caterpillar have started to eat the leaves. Caterpillars will spread inside the box afterwards; for this reason is better to avoid big containers. This is time to add the first fresh leaves inside; caterpillars will sense the presence of the host plant and converge on it. In general, after hatching, caterpillars tend to rest for a while and then spread almost randomly for several hours; sometimes up to few days depending on the species.
Eggs and L1 caterpillars inside 80mm plastic Petri dishes
It is possible to breed caterpillars inside a Petri dish (Check our Petri dishes) for the first instar, in some cases till the second. This method has the advantage of reducing the space in which they can walk around and create a micro-environment in which leaves are drying slower. On the other hand the breeder should clean them more often and be very careful in case of toxic host plants or with species sensitive to overcrowding or ventilation.
The number of L1 caterpillars inside a standard 80mm Petri-dish could range from 5-10 for delicate species (ex. Attacus sp.) to 50 for easy ones as Samia sp. This also depends on the number of times your are able to clean them daily. Usually, we let them hatch inside Petri-dish and then transfer them to small plastic boxes at the beginning of L2. (Check our Plastic Box)
When caterpillars are very small (e.g. L1,L2,L3) they will consume a very small amount of food and the leaves could dry before they have finished to eat them.
To avoid this, place inside the container a small amount of leaves. When it is time to change the food, or clean the box, remove all the old leaves to avoid caterpillars to waste time on them.
If you can, avoid touching the caterpillars, especially when they are in the first instars, they are very sensitive. If you need to move them, try to handle them with a leaf. The trick will be easier using forceps and precise scissors.
If the caterpillars are moulting from one instar to another, they will ancorate to the ground/leaf/box or to wherever they are. They will stay still for a couple of days before breaking the old instar’s cuticole and start moving again. In this phase they need to be left attached to the substrate. Don’t worry if caterpillars sometimes seem too static, they are probably moulting! The amount of food eaten and caterpillars’ activity will increase exponentially during the course of each instar.
Samia ricini, L5 caterpillars in plastic boxes
Starting from L3/L4, caterpillars will consume a larger amount of food and they will be transferred to bigger boxes to avoid overcrowding and allow more space for the host plants. Since caterpillar’s growth is exponential, the major part of the food will be consumed in the last larval instar (usually the 5°). During every instar, larvae will be less active in the first part of the instar. When they get closer to the end of the instar they will spend much more time eating.
Sensitive species do not grow well into plastic containers, as they suffer lack of airflow. In addition, caterpillars could get in contact with their own escrements. For such species it’s possible to arrange a different setup. Cutted branches will be directly put into bottles (see img below) paying attention to block every access to the water, instead caterpillars may get inside and die into the water. Our rearing cages are perfect to this purpose.
Attacus atlas, L3 caterpillars reared vertically
At the end of the last larval instar, caterpillars will cease to eat and expulse liquid stools. This is time for them to look for the right place to pupate: the “wandering” phase. Depending on the species they will look for a different place to pupate. Some of them will just find a branch and spoon between the leaves while others will go to the bottom of the container and try to dig (underground pupators). Underground pupators, as Acherontia atropos, need a separate environment for pupate, as a container with minimum 7-10cm of substrate. Substrate can be made of dry leaves, soft soil, or any similar material as sawdust for rabbits.