Movement behaviour of two social urticating caterpillars in opposite hemispheres.

BACKGROUND

Investigating movement ecology of organisms has economic, societal, and conservation benefits. Larval movement of insects for example, plays many significant ecological roles, and with the expansion of the human population and development, encounters and conflicts with insects have increased. Urticating caterpillars are a health concern to people and animals, especially when they disperse in a gregarious and synchronised manner in areas frequented by humans. and from the southern and northern hemispheres respectively, are two geographically-isolated species of moth with similar gregarious urticating caterpillars that can outbreak causing defoliation and medical issues.

METHODS

Each year from March to May, and caterpillars leave their nesting sites and form head-to-tail processions on the ground in search of pupation sites. This pre-pupation procession behaviour and its associated risk of human contact with and caterpillars were studied and compared in Australia and Italy, respectively. The distance, duration, orientation and response to visible light of the pre-pupation processions were studied in both species to determine general patterns.

RESULTS

In the morning, and processions travelled on average 40 and 16 m per day from the nest in 153 and 223 min respectively, in search for potential pupation sites. pre-pupation processions travelled generally to the north or south when leaving the nest, as was their final orientation to the bivouac/pupation site. Whereas processions had no preference in orientation. and pre-pupation processions travelled towards the darker and the lighter areas of the environment, respectively. During our observations, 27% of and 44% of processions had contact with humans driving, cycling or walking.

CONCLUSIONS

The amount of human contact is surprising and alarming, because of the serious health implications they cause to humans and animals. The processionary dispersal on the ground risks further spread of urticating hairs that can be easily detached, and particular during inadvertent contact. Our limited sample size of processions may benefit from more observations to make conclusive remarks on their pre-pupation behaviour Understanding the movement behaviour of and pre-pupation processions around populated areas is crucial for predicting exposure risk and application of management strategies.