Monarch – 1st Instar » Larval Images

Monarch – 1st Instar

Monarch caterpillar (Danaus plexippus) - 1st Instar

1st Instar – Detail, originally uploaded by eclectic echoes.

Last night someone emerged from it’s egg while we slept. Now 1.5mm long. This is the 1:1 pixel crop.

We’ll be tracking how much it eats and it’s daily growth as a project for my son, as things develop I’ll post updated pictures along with the measurements.

Gender in the monarch larvae

Adult monarch gender is very easy to discriminate using the pouches (spots) in the hind-wings, but for the larvae it’s another story. In the pupal stage there is a small visible difference with females having a line dissecting the 8th abdominal sternite. You may need magnifying glass to find it though. With the larval stages (i.e. caterpillar) there is no external difference at all. If dissected, the male testes can be found as red or pink sac(s) dorsal to the gut in the 6th abdominal segment of late instars.

Classification

Kingdom: Animalia
Phylum: Arthropoda
SubPhylum: Hexapoda
Class: Insecta
Order: Lepidoptera (Butterflies and Moths)
Family: Danaidae (Milkweed Butterflies)
Genus: Danaus
Species: Danaus plexippus

References

Hughes, P.R., Radke, C.D., Renwick, A.A. (1993). A Simple, Low-Input Method for Continuous Laboratory Rearing of the Monarch Butterfly (Lepidoptera: Danaidae) for Research.. American Entomologist, 39:109-111.

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