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Common Blue

Pepe Ao Uri

Zizina otis labradus (aka Zizina labradus labradus)

	Ovum Larvae Pupa Imago Classification Habitat Food Plants Lifecycle

Distribution & Status Common Blue Distrubtion Map

Widespread Found in all of the North Island, Chatham Islands, Nelson, Marlborough, Westland and North Canterbury. It can become very common in some localities. It becomes more plentiful in late summer once numbers have built up throughout the summer.

Observations map

Scientific Classification More info

Family

Lycaenidae

SubFamily

Polyommatinae

Tribe

Polyommatini

Genus

Zizina

Taxon

otis

Also Known As;

Common Grass Blue (Aust), Little Blue

Description

This is probably our most common butterfly, but its small size and flight close to the ground means it is probably the most overlooked butterfly too. It also occurs in Australia, Norfolk Island, Loyalty Islands, Lord Howe Island, New Caledonia and the Cook Islands. It is generally suspected that it has been blown to New Zealand from Australia. Personally I think it was brought to New Zealand by accident in turf from Australia in the 1800's (like has happened with other flora and fauna). Modern farm pasture has allowed the Common Blue to establish in large numbers. This means it is sometimes considered a pest species as one trail recorded over 300 larvae per square metre on a drought-prone pasture. This substantially reduces pasture production due to defoliation of Trefoil's (Lotus spp). The young stages are almost identical to the Southern Blue apart from the pattern on the ovum being different once viewed under magnification and Southern Blue larvae generally have a pinker lateral line, however this is not always definitive. It is one of the few New Zealand butterflies that doesn't appear to have any parasites, however this maybe due to their foodplants naturally containing cyanide or possibly that no parasites have been noticed yet.

Ovum In English

Laid singularly on the underside of foodplant leaves, but can be laid on flowers and buds too. Initially pale green, later turning greenish-blue in colour and a flattened sphere shape which is pitted all over with white ridges. They hatch in about 4 to 6 days.

Larvae In English

Upon hatching it's colourless, but it becomes green or pinkish once it starts eating (the green version is the most common). They have a brown to black head and pale lateral line. They have a double row of long curved setae along the dorsal ridge which become shorter with each instar. it's legs and head are covered by fleshy side flanges, which makes it appear to be head and leg-less. It has a slow gliding slug-like movement. It is almost identical to the Southern Blue, which generally has a pinker lateral line, but this is not definitive. The location is the key to identification in this case (unless your in North Canterbury, when you may have to wait until the imago emerges). The larvae live about 5 weeks and have 4 instars, however 5 instars have been recorded in Australia.

1st instar larvae only chew partway through the leaf and prefer the flower petals. They take about 5 days until their first moult. 2nd instar develops the ability to chew all the way through the leaf, but seldom choose to, instead leaving a 'windowed' leaf with the veins showing. They have a pale lateral stripe. It takes about 6 days to the next moult. 3rd instar larvae develop a darker green dorsal line and faint diagonal markings. It takes a further 7-10 days until its next moult when it's about 9mm long. 4th instar larvae become velvety green with a darker dorsal line and a cream coloured lateral stripe. This instar lasts about 17 days.

From the above timings, I assume it overwinters in the 3rd instar when the larvae move to a sheltered spot in tall vegetation near the base of the foodplant and either spend the winter in a quiescence or diapause. I suspect that it is most likely a quiescence meaning they continue feeding on warmer winter days. Feeding is recorded as resuming in early September when foodplant growth starts. These overwintering larvae go on to pupate in late September, early October. If the larvae runs out of food, then they can pupate successfully, resulting in smaller imagos. Others can become cannibalistic and eat smaller larvae, especially those that are moulting including those that are going into pupation. (This cannibalistic trait is something that many of the Lycaenidae species have). They have being known to have Ants attend to them, but this relationship is yet to be completely understood in New Zealand. Larvae of the Long-tailed Blue are often found on the same foodplant, however the Long-tailed Blue eat the flower and seed pods so do not provide competition for food. Grows up to 15mm when fully grown.

Pupa In English

Variable in colouration from cream through green to grey-brown in colouration with mottled dorsal and sub-dorsal lines to blend in with its surroundings. It has a rounded shape which is mostly smooth with a few short bristles. It is attached by a girdle and weak cremaster formed at or near ground level on a leaf or amongst loose debris. Pupation lasts between about 15 days pupation in summer, but can be up to a month in the spring. The pupa is about 9mm long.

Imago In English

The imago has a 20-27mm wingspan, the average being 24mm. Their flight is generally weak, jerky and fluttering near ground, but can have strong flight if needed. However, their jerky flight can make them very hard to follow as they disappear into 'thin air'. They generally stay close to where the larval foodplants grow, but as these plants are so abundant in New Zealand this can still mean they cover a considerable distance. They often rest on vegetation or rocks with their wings closed on bright days, but will slightly open in a 'v' shape with its head away from the sun when it cools down. I've observed on cloudy days that they will generally rest with their wings in the 'v' position. If in the same habitat, they can be seen flying with the Boulder Copper. Like most blue Butterflies, there is a sexual dimorphism which results in the males having stronger blue colouring with androconial scales and are about 4mm larger then females. The female is a duller grey, usually with only a few blue scales near the thorax. Both genders have silvery grey underside that are dotted with brown and white spots which are variable. They lose their blue colouring and become greyer with age. They roost in grass head down with the forewings tucked under the hindwings, so can be easily disturbed in late evening around sunset.

There are rumours of hybridisation between the Common and Southern Blue in North Canterbury and the Waiho Gorge, however out of the 3 studies that have tackled the subject, 2 (Gibbs 1980 and Gillespie 2010) suspect hybridisation does occur and 1 (Yago et al. 2008) says there is no evidence of hybridisation. Hybridisation in wild populations will be up for discussion until such time as a full study is undertaken. I suspect that the Common Blue has displaced the Southern Blue in the north of the South Island and parts of the North Island as there are 3 areas outside the 'normal' range of the Southern Blue (Central Plateau, Mount Robert and the Waiho Gorge) that they have being reported (none recently that I'm aware of).

Habitat

It prefers areas that have a varied habitat that includes shelter, food including nectar plants and stones for sunbathing. This means it can be found flying close to the ground over lawns, grasslands, roadsides and riverbeds up to 1000m.

Food Plants

Like the Southern Blue, it also oviposits on low-growing plants from the Fabaceae family like Pink Clover (Trifolium pratense), White Clover (Trifolium repens), Hare's Foot clover (Trifolium arvense), Toothed Bur Clover (Medicago polymorpha), Bird's-foot Trefoil (Lotus corniculatus), Greater Bird's-foot Trefoil (Lotus pedunculatus), and Tree Lucerne (Chamaecytisus palmensis). Sometimes recorded on Pea (Pisum sativum) and Broad Bean (Vicia faba).

Lifecycle

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