Caring for a Caterpillar of Hippotion scrofa, SPHINGIDAE
(Photo: courtesy of Bec Watkins, Tarragindi, Queensland)
Because so few Caterpillars of Australian lepidoptera are known, often the only way to identify the species of a caterpillar is to care for it, and rear it to an adult butterfly or moth. This is because most of the naming and classification taxonomy of Australian butterflies and moths was done over 100 years ago on specimens caught in Australia but taken to the British Museum in London, where the entomologists had no idea of the life histories of their specimens. For example: in these webpages, we have pictures of caterpillars in the webpages of less than 1,000 species, compared with over 5,000 webpages for species for which we have adult moth or butterfly pictures.
For people wishing to care for a caterpillar that they have found,
this is what we suggest:
take your caterpillar into captivity to keep ants, spiders, wasps, and other parasitic and predatory insects from attacking it.
Remember that if nature is in balance, then every pair of adults will produce only 2 viable adults in the next generation. Say if a female lays say 400 eggs (a typical number), of which, say, 200 hatch successfully into caterpillars, then on average 198 of these will die before reaching maturity to procreate. So the death rate of caterpillars in the wild is about 99%. Leaving your caterpillar in the wild is basically a death sentence.
A suitable simple container for rearing most caterpillars is a clean glass bottle, with a piece of fabric over the top held in place by an elastic band. In the bottle, it is a good idea to place some dry soil with some dead leaves, and a diagonal stick with algae and/or lichen on it. The soil and dead leaves are for caterpillars that pupate in the ground litter or under the soil. The diagonal stick is for the emerging adult butterfly or moth to hang on to while it expands wings.
In general, you have to capture caterpillars when you see them. Bear in mind that caterpillars can crawl at about half their length/second. For a caterpillar that is say 6 mms long, that equals about 10 metres/hour, so if it decides to seek somewhere nice to pupate or even vary its diet, during 10 hours overnight, it may have burrowed under the soil to pupate or it could be 100 metres away. Either way, you have little chance of finding it the day after you saw it first. So: I always carry a little plastic jar with me when I go out.
To transfer a caterpillar, say into a jar: put a leaf in front of it, and then gently tickle the rear of the caterpillar with something to encourage it walk forward onto the leaf, then you can put the leaf with the caterpillar on it into the jar. It is wise never to touch a caterpillar as the hairs on many species break easily and can cause skin irritation and other medical problems.
The next consideration is whether to feed it. Many caterpillar species hide in the foliage of their foodplant while they are feeding and growing, but go walkabout when they are mature and need to pupate. So if a caterpillar is found walking about rather than on its foodplant, it probably does not need any more food.
There are two exceptions to this. If you notice a totally defoliated nearby plant, bush, or tree, in this case it may be seeking more sustenance. Or if was found on an old fence or wall, it may feed not on leaves, but on Algae and Lichens. So choosing a diagonal stick with algae and/or lichen on it may solve this possibility.
If the caterpillar is immature and needs food, the easy choice of what to feed it is the leaves, buds, or flowers of the plant species it was found on. Most caterpillars are fussy eaters. They can tell from the smell, taste and texture, whether a leaf, etc., is good for them to eat or not. Most caterpillars will just refuse to eat anything that they think is poisonous to them.
Over the last 100 million years : there has been a silent but escalating war and arms race : between plants and caterpillars. Various plants have evolved into over 100 different plant families, each producing different poisons to stop caterpillars eating them. Meanwhile the caterpillars have co-evolved into over 100 different families, each developing different metabolisms, each equipped to cope with the poison typically from one plant family. So incidentally, if you can find the name and family of the caterpillar's foodplant, then that will help identify the caterpillar.
The six basic common Australian caterpillar foods are:
If an unknown caterpillar rejects all five, then rose petals and thinly sliced apple are good standbys. Apparently plants in Rosaceae have developed very few poisons.
Many caterpillars are fussy about their humidity: some like dry conditions, some wet. The sand or soil helps control this. Many caterpillars get quite thirsty: if your animal looks a bit dry: try dipping new food leaves in water before giving them to the caterpillar. Too much water: then mould attacks the caterpillar. Too little: the caterpillar can die of dehydration. Every species has a different balance point.
In due course, with any luck, the caterpillar will pupate in a silk cocoon. Pupation is usually signalled by it ceasing to feed. It may form a cocoon on the side of the container, or under the covering, or in a curled leaf of the food plant, or on a twig, or in the sand/soil. It is best not to disturb the animal while this is happening. In pupating, excess fluid is expelled. Dry sand or soil in the container is good to absorb that away from the pupa.
When pupation is complete (maybe several days), gently (the pupae bruise easily too) take out any loose droppings and excess food plant which would otherwise go mouldy. You should provide some twigs for the new adult, when it does emerge, so that it can hang upside down, as most Lepidoptera need to do this for their wings to expand properly.
You then have to wait. Some adults emerge in 2 weeks, some in 2 years, so this may require some patience. The time depends on the species, the season, the weather, how much food it ate, and just how it feels.
Rearing caterpillars is a skill, and one learns by trial and error. Do not get upset if you do not succeed the first time.
Your patience may also go unrewarded: a high proportion of caterpillars get infected with parasitoids. These are usually fly or wasp species that lay their eggs on or in the caterpillar, and when they hatch, the fly or wasp grub eats the caterpillar from the inside. This tends to make the caterpillar upset and wander about instead of hiding on its food plant: and so these are the caterpillars that are most often found. So if a bunch of flies or wasps come out the pupa, do not be too surprised. These flies and wasps are actually very important. If that is what you get: consider saving them and donating them to your local museum together with information about the caterpillar, especially if you were able to photograph your caterpillar. The information on the various species of wasp or fly that parasitise each species of caterpillar is very important ecological information.
Once you have an adult moth or butterfly, make sure it does not beat itself to a frenzy (butterflies and moths basically do not like being kept in jamjars): a spell in the refrigerator at five degrees Celsius (not freezing which kills them) is a good way of putting them to sleep. Then you may finally be able to photograph it, and identify it from pictures in these web pages, or in books, or with the help of your local museum.
(updated 18 February 2013, 8 August 2023)