Butterflies of the Amazon and Andes
Westwood's Mottled Satyr
Steroma bega  WESTWOOD, 1850
subfamily - SATYRINAE
Steroma bega andensis, Bosque She'llot, Peru  Adrian Hoskins
There are 1150 known species of Satyrinae in the neotropical region. About 600 of these are placed in the subtribe Pronophilina - a diverse group of high altitude cloudforest butterflies, all of which are confined to the neotropical region. The vast majority are found only in the Andes, but 4 species are known from the Atlantic cloudforests of Brazil, and there are a further 6 species that are endemic to Guatemala, Costa Rica or Mexico. More oddly there is one genus Calisto that is found exclusively on the Caribbean islands of Cuba and Hispaniola.
The genera Steroma and Steremnia comprise of small dark butterflies, with a characteristic angular apex, and deeply scalloped hindwings. There are 5 Steroma species - bega, modesta, superba and another 2 species that have not yet been assigned scientific names.
The irregular wing shape and dark mottled pattern of bega and other Steroma species gives them a quite extraordinary resemblance to a tiny clod of earth, making them very difficult to spot when at rest.
Steroma bega is distributed from Colombia and Venezuela to Peru. The subspecies illustrated here - andensis, is found in Ecuador and Peru.
This is a cloudforest species, normally occurring at altitudes above 2000m, although in August 2012 I found a specimen at 450m, amidst a migrating swarm of Marpesia furcula.
The lifecycle appears to be unrecorded. The following generalisations are applicable to the subtribe Pronophilina and probably also apply to Steroma: The eggs are round, white or pale greenish white, and laid singly on the foodplants or on surrounding vegetation. The larvae are typically pale brown, marked along the back and sides with narrow dark stripes, and tapering towards the tail. The head is large in proportion to the body and has two short forward-pointing horns. The tip of the abdomen is equipped with a pair of caudal prongs that are used to flick the frass away from the feeding area. The larvae of all known Pronophilina feed on Chusquea - a genus of bamboo that grows in thickets, mainly along the courses of streams.
Adult behaviour

Males can be found on sunny mornings, in the company of other Pronophilines, imbibing moisture from mud, damp sand or rocks. Like other montane Satyrines they are fairly sedentary by nature, and not easily disturbed when at rest.



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