Olberg R M, Worthington A H, Fox J L, Bessette C E, Loosemore M P
Department of Biological Sciences, Union College, Schenectady, NY 12308, USA.
J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2005 Sep;191(9):791-7. doi: 10.1007/s00359-005-0002-8. Epub 2005 Sep 13.
To determine whether perching dragonflies visually assess the distance to potential prey items, we presented artificial prey, glass beads suspended from fine wires, to perching dragonflies in the field. We videotaped the responses of freely foraging dragonflies (Libellula luctuosa and Sympetrum vicinum-Odonata, suborder Anisoptera) to beads ranging from 0.5 mm to 8 mm in diameter, recording whether or not the dragonflies took off after the beads, and if so, at what distance. Our results indicated that dragonflies were highly selective for bead size. Furthermore, the smaller Sympetrum preferred beads of smaller size and the larger Libellula preferred larger beads. Each species rejected beads as large or larger than their heads, even when the beads subtended the same visual angles as the smaller, attractive beads. Since bead size cannot be determined without reference to distance, we conclude that dragonflies are able to estimate the distance to potential prey items. The range over which they estimate distance is about 1 m for the larger Libellula and 70 cm for the smaller Sympetrum. The mechanism of distance estimation is unknown, but it probably includes both stereopsis and the motion parallax produced by head movements.
为了确定栖息的蜻蜓是否能通过视觉评估到潜在猎物的距离，我们在野外向栖息的蜻蜓展示了人工猎物——用细金属丝悬挂的玻璃珠。我们拍摄了自由觅食的蜻蜓（黄蜻和红斑丽纹蜻——蜻蜓目，差翅亚目）对直径从0.5毫米到8毫米的珠子的反应，记录蜻蜓在珠子出现后是否起飞，如果起飞，是在多远距离起飞。我们的结果表明，蜻蜓对珠子大小具有高度选择性。此外，体型较小的红斑丽纹蜻更喜欢较小尺寸的珠子，而体型较大的黄蜻更喜欢较大的珠子。每个物种都会拒绝与它们头部一样大或更大的珠子，即使这些大珠子与较小的、有吸引力的珠子所张的视角相同。由于不参考距离就无法确定珠子的大小，我们得出结论，蜻蜓能够估计到潜在猎物的距离。对于体型较大的黄蜻，它们估计距离的范围约为1米，对于体型较小的红斑丽纹蜻则为70厘米。距离估计的机制尚不清楚，但可能包括立体视觉和头部运动产生的运动视差。
