Saturniidae (Silkmoths)


Saturniidae in the wild
The Saturniidae, also known as Emperor moths or Silkmoths are a large family of moths that can be found nearly all over the world, with over 2000 species. Despite their nearly global presence, Saturniidae biodiversity is mainly concentrated around the tropics – the majority of Saturniidae are tropical species. The Saturniidae are the among biggest winged insects on this planet; species such as the atlas moth (Attacus atlas) and hercules moth (Coscinocera hercules) have the largest recorded wingspans and wing surface areas of all insects, in rare cases measuring up to 260mm-280mm in wingspan. Saturniidae moths have no functional mouthparts and cannot feed. For this reason the adults are relatively short lived.  Adult Saturniidae moths get their energy from the fat reserves they have stored in their abdomens. Although these fat reserves cannot be replenished for they cannot feed, they provide the moths with enough energy for several days or even weeks, which is enough time for the adults to find a mate, lay eggs after pairing and die. The lifespan of a Saturniidae moth is short and usually varies between 4 and 21 days time (rough estimation); larger species seem to live longer – up to several weeks – while the smallest species usually don’t last longer than a week. Many species of Saturniidae moths spin large silk cocoons to protect their pupae, however some subfamilies refrain from spinning silk and pupate underground or in leaf litter. The caterpillars of Saturniidae are large and are often adorned with spikes or appendages called setae; in some cases, these spines may inject an urticating venom when touched. Because of this, some Saturniidae species are a health hazard, especially in the tropics – some of them have painful or dangerous sting. In the majority of  cases however, the spines and tubercules they carry are not venomous and rather help them blend in with the environment or simply makes it harder to grab or swallow them. Some species do not have any appendages at all and are simply ‘naked’ looking, and some may be hairy instead. Saturniidae rarely sequester toxins and are generally edible although there are a few known exceptions (Arsenura, Eochroa, Ceranchia).

Saturniidae moths strongly rely on smell; the males have large feathered antennae that allow them to smell the females pheromone in order to locate her. Males have a much more active lifestyle and need to fly for miles in some cases to find a partner. For that reason their bodies are often better adapted for flight. Females of most Saturniidae species don’t fly much at all. They appear quite apathic  and inactive and may sit in the same spot for days, waiting for a male to arrive. The females can emit pheromone, a chemical that attracts males. The job of the female is mainly to remain undiscovered and in a secure position, until a male finds her. Because females carry hundreds of eggs and are greater in size, flying is harder for them due to their increased bodymass. The females of some species can be so heavy that they struggle to fly at all. The males however are much more agile because they are smaller, have more aerodynamic, slender wings and bodies. In some cases males and females have a completely different colour (sexual dimorphism). It is only after having recieved the sperm of a male that the females become more active. In this case they will fly or wander around and start to lay eggs. While most Lepidoptera prefer to lay eggs on their host plants, Saturniidae seem to drop them more randomly. Not completely random though; females do have a limited capability to smell and locate their host plants.  However in most cases females are already on their host plants because they don’t tend to wander very far from their cocoons, and most caterpillars pupate in the vincinity of, or even on the bark or leaves of their own food plants themselves. Thus, females feel comfortable with ‘dumping’ their eggs a bit randomly, since most of the time, females are located in the vinicinity of their food plants. Females will also lay eggs if they feel stressed and are being disturbed, attacked or handled; this may help her escape because females are often too heavy to fly very well, and dumping some eggs may reduce her weight, enabling a quicker escape.  It is also a survival mechanism that allows females to quickly leave some offspring in case she dies; leaving some offspring behind in a panic is better than dying without leaving anything in a dangerous situation. Saturniidae are more often than not polyphagous instead of specialists on a single host plant although there are a few rare exceptions.

The adults of Saturniidae are well known and popular collectors items, and generally speaking they are a ‘well-studied’ family. The opposite is true for their ecology however; especially in the tropics, the host plants, ecology and life cycle of even the most common Saturniidae can be unknown.

Saturniidae in captivity
Saturniidae are the most commonly bred moths in captivity. First of all, some species of Saturniidae have economical value and have been bred for hundreds or even thousands of years for the purpose of silk production (sericulture). Some species have even been completely domesticated or are completely man made polyhybrids (Samia ricini, Antheraea pernyi) that were artificially selected for silk production. Secondly they don’t just provide silk, but nutrition too. In some countries it is a common practice to eat the caterpillars or pupae of Saturniidae moths. In Africa, several types of  Gonimbrasia species, Heniocha species and Cirina forda are a popular snack. The larvae are commonly cooked or mashed into a paste, dried out, or added to a stew; and in some cases even eaten alive. In Asia, pupae of several Saturniidae species are cooked, fried with oil, dried or salted and added with fish. This is convenient because some common species of Saturniidae are ubiquitous in tropical countries and are easily collected, bred or farmed in captivity, providing a reliable source of income and food. They are also large species and in most cases non-toxic. Saturniidae rarely sequester toxins and are generally edible although there are a few known exceptions (Arsenura, Eochroa, Ceranchia). And last but not least, their great sizes, spectaculair shapes, colours and the fact that most of them can be easily bred in captivity has made them very popular among amateur entomologists, collectors and breeders that raise them in captivity. Many zoos and tropical butterfly houses have various types of Saturniidae in their displays; commonly seen are the atlas moths (Attacus atlas), comet moths (Argema mittrei) or Rothschildia moths (Rothschildia lebeau) – these are being bred on a commercial level.

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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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The aim of this website is to provide information about many species of moths and butterflies around the world, with a slight focus on rearing them in captivity.

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