Do masquerading of snail poop enhance the protective value of sawfly caterpillars?

Abstract

Anti-predatory mechanisms, such as crypsis, mimicry and aposematism, have evolved to assist prey species to enhance protective efficacy against predation. Masquerade is a type of mimicry where organisms resemble inedible objects so that their potential predators misidentify their prey. Though masquerade is a well-known antipredator mechanism, its efficacy is often not verified or explicitly quantified. Sawfly caterpillars (Hymenoptera: Symphyta) commonly found in monsoonal tropical forests of Xishuangbanna region, southwest China, are solitary and black, and present curled posture when resting, resembling snail excrement. We investigate the protective value of masquerading by these sawfly caterpillars by comparing the predation rates on artificial caterpillars of different colors and shapes. We used green, white and black oil-based, non-toxic clay to make dummy caterpillars in two shapes: straight and curled. We established a total 8 plots (8 m*10 m) in a rainforest and limestone forest at Xishuangbanna Tropical Botanical Garden (XTBG) from 14 th to 20 th November, 2018. At each plot, we deployed 320 caterpillars in different colors and shapes, and recorded presence of predation marks left of the clay caterpillars after 48 hours (a total of 5120 caterpillar-days). Total daily predation rate was slightly higher in the rainforest (13.5%) than limestone forest (12.7%). Among the predation marks left by different groups of predators, insect predation (primarily by ants) was the most common. Predation rate was lower for black and green than white caterpillars, but shapes had no influence. The results of our study suggest that black and green colors are effective in reducing predation but curled postures may have different purposes other than masquerading. Anti-predatory mechanisms are often assumed based on field observation, but our study suggests that such mechanisms should be elucidated.

Full text

Do masquerading of snail poop enhance the protective value of sawfly caterpillars?
Thilakarathne, K.G.D.D.1, NIU Ying2, Ruhama Maya Sari3, Sabita Gurung4, Venus Saksongmuang5,
Takafumi Mizuno2 and Akihiro Nakamura2*
1Postgraduate Institute of Science, University of Peradeniya, Peradeniya, Sri Lanka
2Xishuangbanna Tropical Botanical Garden, Xishuangbanna, Yunnan, CAS, China
3Andalas University, Indonesia
4Small Mammals Conservation and Research Foundation, Nepal
5Department of Biology, Faculty of Science, Prince of Songkla University, Thailand
*Corresponding author: a.nakamura@xtbg.ac.cn
Abstract
Anti-predatory mechanisms, such as crypsis, mimicry and aposematism, have evolved to assist prey
species to enhance protective efficacy against predation. Masquerade is a type of mimicry where
organisms resemble inedible objects so that their potential predators misidentify their prey. Though
masquerade is a well-known antipredator mechanism, its efficacy is often not verified or explicitly
quantified. Sawfly caterpillars (Hymenoptera: Symphyta) commonly found in monsoonal tropical
forests of Xishuangbanna region, south-west China, are solitary and black, and present curled posture
when resting, resembling snail excrement. We investigate the protective value of masquerading by these
sawfly caterpillars by comparing the predation rates on artificial caterpillars of different colors and
shapes. We used green, white and black oil-based, non-toxic clay to make dummy caterpillars in two
shapes: straight and curled. We established a total 8 plots (8 m*10 m) in a rainforest and limestone
forest at Xishuangbanna Tropical Botanical Garden (XTBG) from 14th to 20th November, 2018. At each
plot, we deployed 320 caterpillars in different colors and shapes, and recorded presence of predation
marks left of the clay caterpillars after 48 hours (a total of 5120 caterpillar-days). Total daily predation
rate was slightly higher in the rainforest (13.5%) than limestone forest (12.7%). Among the predation
marks left by different groups of predators, insect predation (primarily by ants) was the most common.
Predation rate was lower for black and green than white caterpillars, but shapes had no influence. The
results of our study suggest that black and green colors are effective in reducing predation but curled
postures may have different purposes other than masquerading. Anti-predatory mechanisms are often
assumed based on field observation, but our study suggests that such mechanisms should be elucidated.
Key words: Masquerade, Sawfly caterpillar, Dummy Caterpillar, Snail poop, Predation