Graellsia isabellae

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Graellsia isabellae -  Spanish Moon Moth

Distribution

• Endemic to mountainous regions of France and Spain. 

• Has been observed in Switzerland as an introduced population; that Swiss population may derive from individuals from Spain and France. 

• The species is often called the “Stained Glass” moon moth. 

• It is a relict species, surviving in stable refugial mountain habitats over long geological times.

Biology & Life Cycle

• Voltinism: Univoltine (one generation per year). 

• Flying period: Adults are found from April to July, depending on local climate. 

• Wingspan: About 60–100 mm (medium-sized) 

• Host plants: Larvae feed only on pines (Pinus spp.), especially Pinus nigra and Pinus sylvestris.

• In captivity, other Pinus species may be accepted, though the moth in the wild is quite specialized.

Rearing & Husbandry Notes

Eggs & Early Instars

• Eggs hatch in 10 to 15 days (depending on temperature) 

• After hatching, larvae should be placed on cuttings of pine (fresh, pesticide-free) in well-ventilated containers.

• Young larvae (L1–L2) can be reared in plastic boxes with ventilated lids. 

Later Instars & Growth

• From L3 onward, larvae may be transferred to sleeves (mesh “bags”) or larger ventilated cages. 

• It is possible to rear the caterpillars from egg to cocoon in ventilated boxes, provided they are kept extremely dry.

• Moisture control is critical: Many breeders fail with G. isabellae because they keep larvae too wet. 

• Replace pine twigs every 3–5 days. Keep the container clean of frass (droppings) and mold. 

• Avoid overcrowding: stress from contact causes smaller, weaker adults and higher mortality. 

Pupation & Overwintering

• After 5 instars, larvae spin cocoons. They can be offered moss or similar substrate in which to spin. 

• Cocoons must be kept dry. They are tolerant of cold and frost, indeed, the species’ wild habitat experiences freezing winters.

• Overwinter the cocoons in a cold, dry place (e.g. cellar, garden shed, or outdoors in garden in many temperate climates). 

• Be cautious with fridges,  humidity inside fridges may dry cocoons too much and lead to death. 

Adult & Breeding

• Some adult males show little or no mating drive (“apathic” males) in captivity this is a known challenge. 

• Hand-pairing is possible but more suited for experienced breeders. 

• One technique: keep virgin females alone, then introduce males at night when females are calling. 

• The species hybridizes readily with Actias genus moths in captivity, showing its close affinity.