Scyrotis athleta (Jumping-ball moth)

Life > Eukaryotes > Opisthokonta > Metazoa (animals) > Bilateria > Ecdysozoa > Panarthropoda > Tritocerebra > Phylum: Arthopoda > Mandibulata > Atelocerata > Panhexapoda > Hexapoda > Insecta (insects) > Dicondyla > Pterygota > Metapterygota > Neoptera > Eumetabola > Holometabola > Panorpida > Amphiesmenoptera > Lepidoptera > Glossata > Coelolepida > Myoglossata > Neolepidoptera > Heteroneura > Incurvarioidea > Family: Cecidosidae > Scyrotis

In the sand and leaf-litter beneath Searsia lucida (= Rhus lucida), one can sometimes see small (about 6 mm) oval balls that jump. In the ball is the larva of a moth, Scyrotis athleta (family Cecidosidae). The movement and jumping is a response to heat and facilitates repositioning of the ball into ideal pupating conditions in the soil and leaf-litter. It is quite a mystery how such a small larva in such a confined space is able to exert the force required to jump (up to 10 cm). Janse (1920) concluded that it is done by careful positioning inside the ball and rapid contracting and relaxing of muscles.

The balls start off as bumps (galls) that form on the leaves of Searsia lucida. A female moth lays her egg probably by inserting her ovipositor into the leaf. The gall is formed around the hatched larva possibly as a result of the feeding action inside the leaf. This is still being investigated. The larva feeds inside the gall and when mature the external layer of the gall bursts open and the ball falls to the ground. Jumping can continue for up to 6 weeks and the moth emerges a few months later.

Gall beginning to develop where a moth egg has been laid on the leaf. [photo V.B. Whitehead, Iziko ]

Gall on leaf of Searsia lucida. [photo V.B. Whitehead, Iziko ]

Gall on leaf of Searsia lucida. [photo V.B. Whitehead, Iziko ]

Gall where the external layer has burst open showing the jumping ball that will fall to the ground. [photo V.B. Whitehead, Iziko ]

Cross-section of the gall revealing the larva within. [photo V.B. Whitehead, Iziko ]

The moth, Scyrotis athleta (wing span about 10 mm). [photo V.B. Whitehead, Iziko ]

 

However, the story does not end there. There are wasps that parasitize the galls. The female wasp of the family Cynipidae lays her eggs in the gall causing the gall to callous, killing the moth larva but allowing the parasitic wasp larva to develop. The calloused gall does not fall from the plant and the 3 mm adult wasps emerge the following year in June.

There are other similar jumping species that occur in South Africa. There is a moth (family Incurvariidae) associated with proteas and another (family Pyralidae) associated with Euphorbiaceae. These are different from the originator of the term, the Mexican jumping bean, that is in fact a seed of a shrub (genus Sebastiana) in which the larva of a moth, Carpocapsa saltitans (family Tortricidae), develops into a cocoon. 

Reference

  • Janse, A. T. 1920. The jumping bean. S. A. Journal of Natural History 2(1): 121-124.

Text by M. Cochrane, V.B. Whitehead and S. van Noort.


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