Natural history of the Brenton Blue

Habitat & vegetation

The Brenton Blue needs a particular habitat for its survival. It lives in a high rainfall area on a south facing dune slope quite close to the sea. The vegetation is a mixture of asteraceous (daisy family) coastal fynbos and coastal thicket. Trees such as candlewood on the site provide partial shade that the butterfly seems to prefer for plants on which to lay its eggs.

Life cycle

The adult butterflies hatch out in late October and November, living for only 2-3 weeks. The males establish and patrol territories seeking and attracting females to mate with.

A mating pair of Brenton Blues

The females advertise their presence by emitting pheromones, which attract the males. The fertilised female lays its 0.6mm diameter white eggs singly on the underside of the leaves of the food plant on which its larvae (caterpillars) feed, whose scientific name is Indigofera erecta. This is a member of the legume (pea) family with a small pink flower. There are two other Indigofera species in the reserve with similar-looking flowers but this butterfly does not use these species.

    

 

 

 

 

 

Brenton Blue eggs on Indigofera erecta                                                                           Indigofera erecta

 

 

 

 

 

 

       Brenton Blue larva                                                                                                                 3rd Instar larva

The larva hatches out of the egg after about ten days and feeds on the leaflets of the food plant until after its second moult, when it reaches the third instar stage. It then crawls down the stem of the plant to the ground and encounters Camponotus baynei ants, which attend the larvae and give it protection from predators. The larvae produce highly palatable and nutritious secretions from honey glands in their skin, on which the ants feed. The ants excavate a hole around the rootstock of the plant, and the larva crawls down onto the rootstock on which it starts feeding. The larvae have a final development stage (the fourth instar) during which they grow to 15-20mm in length before pupating (forming a chrysalis or pupa) in the hole alongside the rootstock.

 

 

 

 

 

 

Hole excavated by ants                                                                                                           4th Instar larva

The host ants, C. baynei, nest in dead wood lying on the ground. The ants that tend the larvae are foraging ants that return to the nest to share the nutritious exudations of the O. niobe larvae with their own young.

From the eggs laid in October and November, adults hatch out in the following January/ February. Sometimes there is a small third brood in April if weather conditions are favourable.

Ants tending to larvae