How can bumblebees tell whose traces are on a flower?
花上没有留言，熊蜂怎么分辨谁来过？
一朵花看起来没有变化，但对熊蜂来说，上面可能已经留下了访问记录。
A flower may look unchanged, yet to a bumblebee it may already carry traces of previous visits.
这些记录不是字，也不一定是能看见的脚印，而是脚接触表面时留下的气味物质。
These traces are not writing or necessarily visible footprints, but scented substances left when the feet touch a surface.
布里斯托大学二〇一七年介绍的研究发现，熊蜂能把几类这样的气味分开。
Research described by the University of Bristol in 2017 found that bumblebees could distinguish several kinds of these scent marks.
实验里，研究人员提供有奖励和没有奖励的花，同时安排不同来源的足迹气味。
In the experiments, researchers offered rewarding and unrewarding flowers carrying foot-scent marks from different sources.
有的留着熊蜂自己的气味，有的来自同巢的姐妹，有的来自别巢，还有的没有标记。
Some bore the bee’s own scent, some that of sisters from its nest, some that of bees from another nest, and some were unmarked.
结果，熊蜂不但能区别同巢与外来的气味，也能区别自己与同巢姐妹留下的痕迹。
The bees could distinguish not only nest-mate scents from outsiders’ scents, but also their own traces from those of sisters in the same nest.
这说明它们能利用很细的气味差别，而不是只判断花上有没有任何气味。
This shows sensitivity to fine scent differences, rather than merely whether a flower has any scent mark at all.
研究者认为，这种能力可能帮助它们记住最近去过的花，提高寻找食物的效率。
The researchers suggested that this ability could help them remember recently visited flowers and search for food more efficiently.
不过，分辨几类痕迹，不等于知道每只陌生熊蜂的身份，更不等于准确算出了花里还剩多少花蜜。
Distinguishing categories of traces does not mean knowing each unfamiliar bee’s identity, let alone calculating exactly how much nectar remains.
我们眼中的一片花瓣，对熊蜂来说，还可能带着值得参考的气味线索。
A petal that seems plain to us may carry scent clues worth consulting for a bumblebee.
