COP15昆明生物多樣性保護民間實踐|作家半夏:與蟲在野

Pinellia, a plant of the Araceae family, is native to the wild。

半夏,一種天南星科植物,生於荒野;

The writer, Banxia (Chinese Pinyin of Pinellia), once put aside an unfinished novel and walked out of her study, into the wilderness。

作家半夏,擱置未完稿的小說、走出書房,縱身荒野。

COP15昆明生物多樣性保護民間實踐|作家半夏:與蟲在野

Ban Xia is interviewed by journalists。 By Zhou Mi

半夏接受記者採訪。周密攝

For five years, she has been rooted in the earth within the world of insects, looking at the wisdom of their survival, the ways they love and reproduce, and their short lives as individuals but their long lives as populations。 Finally, she has converted her insights and pictures into essays on natural science in In the Wild with Insects。

整整5年時間,她俯身春城大地,深入昆蟲世界,看它們的生存智慧,看它們的愛情和繁衍,看它們作為個體來說短暫、作為種群來說偉大漫長的一生,並將其中的感悟和拍得的圖片匯入自然博物隨筆《與蟲在野》。

COP15昆明生物多樣性保護民間實踐|作家半夏:與蟲在野

The delicate cover of In the Wild with Insects。 By Zhou Mi

《與蟲在野》精美的封面。周密攝

Abandoning the prejudice of anthropocentrism in the world of insects, she experienced how “if plants and insects are safe, people will be free,” a shared-community ideal。 Connecting nature with literature, she has called for “nature to be restored。”

拋棄人類中心主義的偏見,她在蟲的世界裡體會到“草蟲安妥,人得自在”的生命共同體理念;用文學接駁自然,她發出“對自然必須克己復禮”的呼喊。

A biology graduate, media figure, writer and “wilderness detective,” Banxia can switch from one role to another but has never abandoned “nature” and “words。” Now she has the new mission of being a biodiversity conservation advocate。

生物系畢業生、媒體人、作家、“荒野偵探”……眾多角色流轉切換,卻始終沒有脫離“自然”和“文字”,如今,她又揹負上了新的使命:生物多樣性保護的宣傳者。

野地裡的救贖

Salvation in the Wild

Recently, Banxia had been busy with the promotion of her new book Plane Tree Cafe, the first draft of which was completed in 2014 after having lived in the city of Kunming for nearly 40 years。 At the time, upon setting her pen down, she felt hollowed out。 On a walk after the rain one day, she happened to use her cell phone to capture a lily fly resting on a banana leaf, and the stunning beauty of the sight thus drew her into the world of insects。 Putting down the book in her hands, she began to read the “book of nature,” and while fighting to drag her unwell body along the road, nature redeemed her。 On this journey of reading nature, she not only wrote this book of natural observations but also managed to heal her body and mind。 In 2019, Banxia returned to the limelight with In the Wild with Insects, as if revived, and Plane Tree Cafe, which had been shelved for several years, followed。

最近,半夏忙於新書《懸鈴木咖啡館》的宣傳推廣,這本書寫她生活了近40年的昆明城故事的作品2014年就完成了初稿,彼時,擱下筆,她覺得自己被掏空了。一次雨後散步,她偶然間用手機拍到了一隻停歇在美人蕉葉片上的麗蠅,令人震撼的美讓她從此走入昆蟲的世界。放下手中的書,她開始閱讀大自然這本書,儘管拖著病體,卻得到了大自然的救贖,在閱讀自然這條路上,她不僅寫出這本自然觀察筆記,身心也得到修復。2019年,她帶著《與蟲在野》重回人們的視野,彷彿滿血復活,擱置數年的《懸鈴木咖啡館》也隨後面世。

“In wilderness is the preservation of the world” — Thoreau’s quote struck Banxia deeply。

“野地裡蘊含著對這個世界的救贖。”梭羅的這句話讓她深以為然。

What led Banxia out of her studies and into the world of insects? That chance encounter with the green-headed fly in 2014 was obviously not enough to explain this momentous decision, because not everyone will chase the world of insects selflessly for the splendor of just one insect。

是什麼引領書房裡的半夏走入昆蟲世界的呢?2014年那場與綠頭蒼蠅的偶遇顯然不足以解釋這場重大的決定:不是每個人都會因為一隻蟲的絢麗而去忘我地追逐整個昆蟲的世界。

COP15昆明生物多樣性保護民間實踐|作家半夏:與蟲在野

Ban Xia takes photos of insects in the field。

野外拍蟲的半夏。

Banxia’s childhood experience provides an answer。

童年經歷給出了答案:

Born near a Huize lead-zinc mine, Banxia grew up as a child who liked to “play in the wild。” In the free and vast environment of the mine, she would explore nature by picking fruit from the mountains and collecting rocks from the river。 When she entered college, she chose to study biology。 Jane Goodall, a zoologist who had traveled alone to the primeval forests of Africa to study chimpanzees, was her idol。

出生在會澤鉛鋅礦的半夏從小就是個喜歡“打野”的孩子,廠礦自由廣闊的環境裡,上山摘果、下河撿石頭是她摸索自然的開始,高考填志願,她清一色填報了生物系,獨自前往非洲原始森林研究黑猩猩的動物學家珍妮·古道爾是她的偶像。

After graduating from Yunnan University with a degree in biology, Banxia took a detour and joined a newspaper as a media figure, thus making a name for herself in the field of literary creation。 Intentionally or not, she remained inextricably linked to the profession and hobby that she had once “betrayed,” as most of the titles of her books were related to plants, trees and insects (The Forgotten Flowers, Wormwood of the Heart and Plane Tree Cafe, among others)。 Indeed, her documentary work Watching Flowers Is a World View presents the world of natural science to readers through the floral experience of Liu Huajie, a naturalist at Peking University。 In addition, Banxia enticed the local government to explore the possibility of the “Fushou snail” of Fuxian Lake becoming a media figure。

從雲大生物系畢業後,她卻陰差陽錯進入報社成為媒體人,並在文學創作領域嶄露頭角。有意無意間,她與曾經“背叛”的專業和愛好有著絲絲縷縷的聯絡:著作中大部分書名都與草木蟲豸有關(《忘川之花》《心上蟲草》《懸鈴木咖啡館》等),紀實作品《看花是種世界觀》借北大博物學家劉華傑的逐花經歷向讀者呈現了博物學世界,曾以媒體人的身份喚起地方政府對撫仙湖福壽螺“宣戰”……

To her surprise, In the Wild with Insects was well received by all parties after its release, and the book won many awards, such as “China’s Top Ten Good Nature Books: Natural Life Award” by the Alibaba Public Welfare Fund, the “Qijun Prose Award: Special Award” by October magazine, the “Sina Good Book List: Recommended Book of the Year 2019” and the “Wu Dayou Science Creation: Good Work Award。” In the Wild with Insects was hailed as China’s Souvenirs Entomologiques。 Banxia is most pleased with the enthusiasm for nature that has been generated by the book。 People who had been afraid of insects since childhood have started to gaze at the microscopic world of insects as she does, and children at her sharing sessions have been excited to discuss the life cycle of insects with her。 Inspired by Banxia, increasingly many people have begun to appreciate the beauty of nature’s subtleties。

令她始料未及的是,《與蟲在野》上市後受到各方好評,先後獲得由阿里巴巴公益基金等評出的“中國十大自然好書·自然生活獎”,《十月》雜誌評出的“琦君散文獎·特別獎”,新浪好書榜2019年度推薦圖書,吳大猷科普著作獎·佳作獎等多個獎項,被譽為中國的《昆蟲記》……最讓她欣慰的,是以書為媒凝聚起的關注自然的熱潮,有自小怕蟲者學著她的樣子開始凝視蟲的微觀世界,有分享會上小朋友興奮地和她探討蟲的生命源流,在她的啟發下,越來越多人開始欣賞自然細微處的美好。

COP15昆明生物多樣性保護民間實踐|作家半夏:與蟲在野

One of the awards of In the Wild with Insects。

《與蟲在野》獲得的獎項之一。

Critic Xie Youshun says that a writer, beyond one’s own selfishness, has to see that there is a wider world that deserves attention。 In Banxia’s view, the mission of In the Wild with Insects is to provide a method of survival: to release a little bit of human “sanity” and play well with the little things in nature。

評論家謝有順說:一個作家,在一己之私以外,還要看到有一個更廣大的世界值得關注。在半夏看來,《與蟲在野》的使命就是提供一種生存方式:把人類的所謂理智釋放一點點,跟自然界裡的小東西玩好一點。

與自然玩好一點

Playing Well with Nature

How should one play well with such little things? “Go。 Go into the wild and share a common fate with those wild beings。”

怎麼跟這些小東西玩好一點?“去,去自然的野生環境裡,與那些野性的生命共呼吸或共命運。”

At first, the camp where she would photograph insects was a vegetable field in a fishing village next to Dian Lake。 Every morning, breathing the fresh air, she would walk along a river into the nearby fishing village and buy vegetables from the villagers’ own land。 This vegetable field, free from pesticides, was a paradise for insects in which she could photograph no less than 200 species。 Soon, however, an excavator came: the vegetable field disappeared, and a tall building went up。

起初,她拍蟲的營地是滇池邊一個漁村的菜地。每天早晨,呼吸著新鮮的空氣,沿著一條入滇河道走到附近漁村,買村民自留地裡的蔬菜,沒有用殺蟲劑的菜地是蟲蟲的天堂,她盡情地拍到不下200種蟲子。然而很快,挖掘機開來了,菜地沒有了,高樓起來了。

With the nearest place to photograph insects now history, her fascination with the insect world overwhelmed her。 Banxia started walking toward the western hills and their dense forest where there are more wild flowers。 Often she would only take a bottle of water, a little solid food and a cell phone, spending the entire day walking。 Gradually, her scope for photographing insects expanded to Changchong Mountain, Guanyin Mountain and even Pu’er and Xishuangbanna。 When the shooting gets exciting, her feet go numb making them hard to move。 If she “strikes gold,” she rewards herself by taking the cable car down the mountain。 Over the past five years, she has accumulated tens of thousands of pictures of insects on her cell phone, and she remembers the place, time and habitat of each insect clearly。 She also has memos that record all of their stories。

最近的拍蟲地沒了,對蟲界的著迷卻讓她無法自拔,她開始走向西山,走向野花更多的密林處。常常,一瓶水、一點乾糧、一部手機、一個人,就是一天。慢慢地,拍蟲半徑擴大到長蟲山、觀音山,甚至普洱、西雙版納。拍得高興時,起身雙腳麻木,幾乎挪不動步子。如果有意外收穫,她會獎勵自己坐纜車下山。5年來,手機裡積累了幾萬張蟲蟲的圖片,每隻蟲的拍攝地、拍攝時間及生境她都異常清晰地記得,它們的故事都有一個備忘錄。

COP15昆明生物多樣性保護民間實踐|作家半夏:與蟲在野

Ban Xia looks for insects on Changchong Mountain Kunming。

半夏在昆明長蟲山尋找蟲子。

With her mind and body in the wild, she immediately forgets herself and falls into nature, becoming a flower when looking at flowers and an insect when looking at insects。

身心在野的姿態讓她一下子就棄了糾結著的小我,沒入自然,看花時變花、看蟲時為蟲。

The sight of a ladybug with its open wings broken by thorns, as well as that of small black ants dragging the corpse of red ants three times their size, caused her to sigh over the fact that life is not easy and ultimately ends in death。

看到張翅欲飛的瓢蟲被荊棘折翼、小黑蟻拖著三倍大的紅蟻屍身艱難前行,她不禁唏噓:眾生不易,皆向死而生;

After taking pictures of an insect with a “human face,” she reflected on the fact that being born as a human, one cannot help but be self-centered。

拍下有著“人臉”的蝽蝽後,她反思:生為人類,不由地便以自我為中心;

Witnessing a moth slowly running out of its last bit of energy, she recalled Virginia Woolf, a writer who compared herself to a moth, and her life of intertwining light and darkness, as well as cold and heat。

目睹一隻蛾子慢慢耗光最後一點生命之力,她想到拿飛蛾自比的作家弗吉尼亞·伍爾夫,以及她交織著光與暗、冷與熱的一生;

When she spent countless summer nights in a wetland park to observe a “night club” of insects under a light pole, she was moved by how the wildlife appeared in different periods and shared time and space in a tacit manner。 Meanwhile, she was reminded of Wu Zetian, who violated ecological ethics and ordered all flowers to bloom against their nature, as well as King Wu Yue, the romantic monarch who wrote the lines, “The flowers in the fields are blooming。 Enjoy the flowers and return unhurried。”

而無數個夏夜在溼地公園的燈杆下觀察蟲蟲的“夜總會”,她被野外生命分時段出場、默契分享時空的本分所感動,同時聯想到不遵循生態倫理、下令百花逆天齊放的武則天,以及書寫了“陌上開花,可緩緩歸矣”的浪漫君主吳越王。

From Erya to Tao Te Ching, from Walden Lake to The Wilderness Detective, and from the village woman in the age of poetry to Mother Teresa, if you read In the Wild with Insects, your mind will jump from one such idea to another。 You will find that the vast natural world makes the writer’s vision and thoughts extend into infinity, and the writer’s boundless imagination will cause you to marvel at every step。

從《爾雅》到《道德經》,從《瓦爾登湖》到《荒野偵探》,從詩經時代的村婦到特蕾莎修女……讀《與蟲在野》,思維是跳躍著的,廣闊的自然天地讓作家的視野和思緒無限延伸,作家無垠的想象又讓讀者步步驚歎。

Banxia does not, however, want to sublimate some kind of spiritual realm from plants and animals, as did the ancients。 “An objective and natural record is my pursuit,” she says。 For this, she insists on using her cell phone to take pictures of insects in their habitats, thus using the simplest tools to record the most natural of lives。 She also hopes to encourage more people with cell phones to see forms of beauty that they have never seen before。

然而,她不願像古人那般總要從動植物中昇華出某種精神境界,“客觀自然的記錄是我之追求”,也因此,她堅持用手機拍下生境中的昆蟲,用最簡單的工具記錄最自然的生命,她也希望帶動更多人持一個手機便可看見不曾看過的美。

在浪費時間中獲得樂趣

Having Fun Wasting Time

Having observed insects for a long time, Banxia’s friends often jokingly remark that “she seems to know the language of insects。” When she goes out with her friends, she usually mutters to insects nearby: “Come on。 Come on, little thing!” Then, insects fly to her fingertips, which often amazes and draws the envy of her friends。 She reveals biological laws behind “mysticism”: that is, her special physical constitution of sweet-smelling blood and body heat excites insects, thus naturally attracting them to fly toward her while she hums a ditty。 In her essay In the Wild with Insects, which is full of cultured thinking, professional words are everywhere, such as “lepidopteran moths,” “dipteran mosquitoes,” “orthopteran locusts,” “hymenopteran ants,” “phototaxis,” “thermotaxis” and the “hygrotaxis” of insects。 Although the book is not a serious professional treatise on popular science, it is nonetheless extremely scientific and rigorous。

與蟲玩得多了,半夏被朋友揶揄“像是懂蟲言蟲語了”,一起出去玩,她嘴裡念著“來啊來啊小東西!”,蟲子便飛到她的指尖,面對朋友的驚歎豔羨,她揭示了所謂“通靈”背後的生物學規律——血甜、體熱的特殊體質,讓蟲子興奮異常,自然哼著小曲奔赴而來。充滿人文思考的《與蟲在野》中,專業性詞彙也隨處可見,鱗翅目的蛾、雙翅目的蚊、直翅目的蝗、膜翅目的蟻,蟲蟲的趨光性、趨熱性、趨溼性……不是一本正經搞科普的專業論著,在科學性上卻一點也不含糊。

COP15昆明生物多樣性保護民間實踐|作家半夏:與蟲在野

In the Wild with Insects exhibits numerous photos of insects taken by the author。

《與蟲在野》展示了作者拍攝的大量蟲蟲照片。

This is not only due to Banxia’s biology background but also due to her studies bent over her desk at night after countless days spent with insects in the wild。 Every time she goes out to shoot insects in the wild for a day, hundreds of photos will be added to her mobile phone。 But since she does not know the names of the protagonists in these photos, so must pick up a magnifying glass to meticulously explore them under a lamp at night。 It is not easy to classify insects。 Some of them look the same from their physiques, but they have different spots and different numbers of tentacle segments; in this case, they would belong to completely different species。 There are about 15 million kinds of creatures in the world, of which insects account for two thirds。 About 1。9 million insects have names, whereas the remaining more than eight million insects are still waiting for human beings to discover and name them。 In her study are large books such as China‘s Insect Ecology Illustrated Handbook and Insect Genealogy as well as natural books such as Silence on an Inch of Land and Nabokov’s Butterfly。 As she takes more and more photos of insects, she spends more and more time studying and identifying insects on her computer and in the data at hand every day, meaning that her eyesight grows weaker from spending so much time looking at the screen。 But her eyesight also becomes more acute during field training — so much so that she can identify tiny whiteflies or eggs less than one millimeter in size。

這不僅得益於半夏的生物學教育背景,更來自於無數個與蟲在野的白天之後伏案學習的夜晚。外出去野地裡拍一天蟲,手機裡多出數百張照片,它們姓甚名誰卻不知道。夜晚,她便拿著放大鏡在燈下探究。昆蟲分類著實不易,有時體格外觀看起來一樣,斑點不同、觸角的節數不同,就是完全不同的種。世界上約有1500萬種生物,昆蟲佔去三分之二,有名有姓的約190萬種,還有800多萬種等著人類去發現、去命名。在她的書房裡,既有《中國昆蟲生態大圖鑑》《昆蟲家譜》這樣的大部頭,也有《一平方英寸的寂靜》《納博科夫的蝴蝶》等自然讀物。蟲拍得多了,每天空閒時間在電腦上及手邊的資料裡研究辨識昆蟲的耗時漸長。她的視力在熒屏前越來越弱,卻在野外訓練得更加敏銳了,1毫米不到的細小粉蝨或蟲卵都能迅速甄別。

COP15昆明生物多樣性保護民間實踐|作家半夏:與蟲在野

COP15昆明生物多樣性保護民間實踐|作家半夏:與蟲在野

COP15昆明生物多樣性保護民間實踐|作家半夏:與蟲在野

COP15昆明生物多樣性保護民間實踐|作家半夏:與蟲在野

Ban Xia took photos of insects with her mobile phone。

半夏用手機拍下的蟲蟲照片。

After putting aside writing, Banxia injected all of her energy into insects。 At first, her family thought she was crazy。 “You’re 50 years old, but you’re still taking pictures of insects near the ditch and on piles of poop!” Although her son was upset with her, whenever she wrote a book he would still remind her that “it is not enough for your book to simply encourage people to discover beauty。” Also, her husband would drive her to the places where she wanted to photograph insects without complaint, and sometimes he would help her take important white-background pictures。

放下寫作,所有的精力都在蟲子上,起初,家人都覺得她瘋魔了,“都50歲了,還趴在水溝邊、糞便旁拍蟲!”兒子儘管不滿,但還是會在她寫書時提醒,“只喚起人們發現美是遠遠不夠的”。丈夫會毫無怨言地開車送她去拍蟲的地方,有時還幫她拍一些重要補白的圖片。

“If you can have fun wasting your time, you are not wasting your time。” She uses the words of Earl Russell, a Nobel Prize winner in literature, to define her five years of “abandoning herself in the wild。”

“你能在浪費時間中獲得樂趣,就不是浪費時間。”她用諾貝爾文學獎獲得者羅素的話來定義“拋荒”的這五年。

讓文學和自然嫁接在一起

Grafting Literature onto Nature

“Regional differences have a great influence on the lives of insects。 In Yunnan, people who photograph insects can take advantage of the region’s good, local biodiversity。” On the other hand, Banxia believes that the writers in Yunnan should make full use of the advantages of biodiversity, grafting literature onto nature, thus arousing more people’s awareness for the wild。 In the Wild with Insects presents her lifestyle, which she expects to deliver to readers — a lifestyle that is about playing with lives as tiny as those of insects, as taking care of their lives is to take care of our own destinies。

“昆蟲生活的地域性差異很大,拍蟲者在雲南是得生物多樣性的好,得天獨厚。”反過來,半夏認為,雲南作家應該利用好生物多樣性的優勢,讓文學和自然嫁接在一起,喚起更多人的自覺。《與蟲在野》就是她向讀者提供的一種博物生存方式:跟蟲蟲這樣微小的另類生命玩在一起,關照蟲的生命就是關照我們人類自己的命運。

COP15昆明生物多樣性保護民間實踐|作家半夏:與蟲在野

COP15昆明生物多樣性保護民間實踐|作家半夏:與蟲在野

Ban Xia shoots insects that are breeding。 (All of these photos were provided by Ban Xia。)

半夏鏡頭下正在繁衍的昆蟲。(以上圖片均為半夏提供。)

Over her many sharing sessions, her classes given to children touch her the most。 With her book In the Wild with Insects, Banxia went to Yunnan University Secondary School and many other schools in Luoping and Qujing to share stories with children about playing with insects。 Her colorful vocabulary and vivid descriptions, such as that of a yellow dragonfly wiping tears like a sad old man, a lacewing in a wedding dress, a big colorful mosquito with a noble back and a self-affected damselfly, firmly grasp the children’s attention。 She is amazed by the questions that children raise without the prejudice of anthropocentrism。 She often talks for an hour or two, and if the children do not want to rest, she gives it her all, collapsing as soon as she finishes talking and requiring staff to help her step down。

眾多場分享中,孩子的課堂給她的觸動最多。她帶著《與蟲在野》,先後到雲大附中,以及羅平、曲靖多所學校與孩子們分享和蟲蟲玩在一起的故事。不斷拭淚如悲傷老人的黃蜻蜓、披著婚紗裙的草蛉、有著高貴背影的炫彩大蚊、顧影自憐的豆娘,豐富的詞彙、生動的描繪將孩子的注意力牢牢抓住,不帶人類中心主義偏見的孩子提出的問題讓她驚歎不已。常常一講就是一兩個小時,孩子們不願休息,她也像打了雞血,講完就虛脫了,直到工作人員把她攙扶下去。

She knows that if this knowledge spreads, it will affect children’s attitudes toward nature throughout their entire lives, ultimately affecting an era。 As such, she has two natural books for children to be published soon, and she is about to begin a series of public lectures in schools。 “A single spark can start a prairie fire。” Banxia’s self-orientation is to be a “propagandist for biodiversity conservation。”

她知道,這些火種播下去,會影響孩子一生對待自然的態度,進而影響一個時代。接下來,她有兩本給孩子的自然讀物即將出版,一連串進學校的公益講座排著隊,星星之火、可以燎原,“生物多樣性保護的宣傳者”是她給自己的又一個定位。

“Because of the Biodiversity Conference (COP15), Yunnan province seems to be at the forefront of the world。 I am proud of this and full of expectation。” Her understanding of biodiversity includes three meanings: species diversity, ecosystem diversity and genetic diversity。

“因為生物多樣性大會(COP15),整個雲南好像處在世界的潮頭,我很自豪,也挺盼望的。”在她的理解中,生物多樣性包括三層含義:物種的多樣性、生態系統的多樣性、遺傳基因的多樣性。

What characterizes an ideal city that practices the concept of biodiversity? Banxia suggests that, first of all, nameplates should be set up for all plants。 “We should help ordinary people learn the family and genus of each plant that they encounter in the park or on roadsides so that everyone will naturally care for them。” Second, Banxia suggests that the diversity of urban vegetation be maintained: “Don’t plant trees that are popular online on every street。 The best state is one in which all kinds of life continue to bloom and all kinds of flowers compete to flourish。”

一個理想的踐行生物多樣性理念的城市是什麼樣的呢?她建議,首先,對所有的植物定名牌,“讓老百姓在公園、路邊遇到一棵植物,看一眼名牌就知道叫什麼,什麼科什麼屬,大家自然就會關心愛護它們”;其次,要保持城市植被的多樣性,“不要因為一種樹成了網紅,條條街道都種上。最好的狀態應該是各種生命接續綻放、次第花開。”

“Only when insects live freely and plants thrive can human life be quiet and happy。 We should remain in awe of all life that coexists on earth。 All lives, including those of insects, form a community with human beings。 Thus, human life is of great importance, and insect life is of great importance too。 The periodic rhythm of all life is like polyphonic music — all its parts are independent but also harmonious and unified。 All things grow together endlessly amid light and dust, naturally and with ease。” This is Banxia’s sincere appeal to humankind based on her observation of insects。

“蟲安妥,草自在,人類方安然自得,所有的生命皆須敬畏。共生於地球的所有生命,包括蟲在內都與人類是生命共同體,人命關天,蟲命也關天。所有生命物種的週期節律如復調音樂,聲部各自獨立卻又和諧統一,萬物生、生生不已。和光同塵,自然自在。”借看蟲,她向人類發出真誠的呼籲。

責編:楊芮

編審:周曉雪

終審:錢紅兵