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Monarch butterflies
The kahuku/monarch butterfly (Danaus plexippus) is the final stage of the monarchs life cycle.
Butterflies are insects so they have a head, thorax and abdomen (Figure 1).
Figure 1. Some of the most easily seen parts of a monarch butterfly.
Monarch head
Mouthparts
Monarch butterflies feed on nectar, which they obtain using their proboscis. The proboscis coils up when not in use (Figure 2).
Antennae & palps
Monarchs have a pair of antennae (Figure 1) that allow them to sense touch and smell1.
The labial palps are next to the proboscis and they also detect scent2 (Figures 2 & 3).
Eyes
Monarchs have large compound eyes (Figure 3). These see colour and motion, with a large field of view. However compound eyes are not so good at judging distance or patterns1.
Monarch wings
The two forewings are attached to the 2nd segment of the thorax. The two hind (back) wings are attached to the 3rd segment of the thorax (Figure 1). The forewings are "broad and triangular while the hind wings are more rounded"3.
The wingspan of a monarch is approximately 9-10 cm4. The wings are covered in small scales (Figure 4) that have multiple functions. They retain heat, provide insulation, assist escape from predators, and improve the butterfly’s aerodynamics by enhancing lift and reducing drag5.
Male monarchs have a black patch on their hind wings (Figure 5), and are slightly larger.
Monarch flight is "slow and sailing' [3] reaching speeds averaging ~9km/hr6.
Monarch legs
All 3 segments of the butterfly’s thorax have a pair of legs. However the front pair are very small and held against the body3, so it appears they only have 4 legs (Figure 6). The forelegs are even more reduced in males than females7.
Female monarchs have chemoreceptors on their legs that help them to determine which plants are suitable for egg laying1.
The most obvious sections of the legs are the femur, tibia and tarsus (Figure 6). The tarsi detect suitable food for the butterfly8.
The tarsus each end with a claw (Figure 6). The claws are used to cling to vegetation and when overwintering/roosting (Figure 7).
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References
1. Monarch Watch : Biology : Sensory Systems : Touch. https://monarchwatch.org/biology/sense1.htm.
2. Gullan, P. J. & Cranston, P. S. The insects: an outline of entomology. (Wiley-Blackwell, 2010).
3. Grant, E. A. An illustrated guide to some New Zealand insect families. (Manaaki Whenua Press, 1999).
4. Monarch (Danaus plexippus). iNaturalist NZ https://inaturalist.nz/taxa/48662-Danaus-plexippus.
5. Butterfly Scales. Monarch Joint Venture. https://monarchjointventure.org/images/uploads/documents/Butterfly_Scales_LC36.pdf
6. Klots, A. B. A Field Guide to the Butterflies: North America east of the Great Plains. (Houghton Mifflin, 1979).
7. Gibbs, G. W., Berndt, Lisa, Pawson, S., Gibbs, G. W., & Entomological Society of New Zealand. The monarch butterfly in New Zealand. (2013).
8. Monarch Watch : Biology : Anatomy. https://monarchwatch.org/biology/index.htm.
9. Moths and Butterflies of New Zealand Trust - Pūrerehua Aotearoa.
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