Bombardier Beetle 氣步甲

張一愷/文　張建軍/譯

I will never forget the thrill of discovering that place. A huge clearing unfolded before my eyes， so vast that it revealed the undulating forms of the mountain beneath; a row of trees stretched into the distance forming a neat fence around its perimeter， which suggested that this was the work of professional loggers rather than locals. There was a steady drizzle out here， which was completely unnoticeable earlier in the forest; moon shimmered with a blue radiance， casting down the shadows of dark clouds as they passed over the crescent.

我永遠也不會忘記發現這個地方時的興奮。一塊巨大的空地展現在我眼前，巨大到可以由此看到下面起伏的山脈形狀；一排樹木伸展至遠方，形成了周邊整齊的藩籬，表明這是專業伐木工而不是當地人的杰作。天上細雨綿綿，剛才在森林里時我卻渾然不覺。月亮閃耀著藍色的光芒，烏云越過月牙時投下暗影。

I scanned my searchlight across the ground， and instantly picked up the metallic reflections from several ground beetles. As Max had predicted， the muggy atmosphere triggered the activity of thousands of slugs and snails， which in turn lured out the nocturnal predators that preyed upon them. The sight of this swarm was a real confidence boost—Carabus was a predatory ground beetle， albeit of a giant kind， and there should be no reason why it wouldn’t be here to capitalise on the banquet as well. In the space of an hour I collected at least ten different species of ground beetles. Most were about half an inch long and had shiny black shells， which occasionally glowed with a metallic lustre of greens and purples. One kind， however， was garishly dressed in a combination of black and yellow so that it stood out from all the rest. I had never seen such a beautifully coloured ground beetle before， and in the heat of the moment I neglected nature’s most obvious warning sign as I reached my hand towards it—after all， it’s not a wasp， so it can’t sting. Right？

我用手電光搜索著地面，立刻發現了幾只步甲身上反射出的金屬光澤。正如馬克斯預測的，悶熱潮濕的環境引發了成千上萬只鼻涕蟲和蝸牛的活動，這繼而又誘出了那些以它們為食的夜行獵食者?？吹竭@一大群蟲子，我信心大增：大步甲正是一種掠食步甲，盡管是很大的那種，它沒有理由不來此享用盛宴。一個小時之中，我就捉到了至少10種不同的步甲。它們絕大多數約半英寸長，有著亮黑色的甲殼，有時候也會發出各種綠色和紫色的金屬光澤。然而，有一種步甲可謂“鶴立雞群”。它有著炫目的黃和黑的混合色，我以前從來沒有看到過色彩如此美麗的步甲。一時興起，我忽略了自然界最顯見的警告標識，朝它伸過手去。畢竟，它不是一只大黃蜂，所以它不會蜇人，對吧？

‘Ouch！’ I gave a yelp of surprise as my fingers burned with a scorching sensation. Leaving behind a high-pitched ‘pop’ and a plume of smoke from its rear end， the beetle had disappeared into the depths of a tussock nearby. A brown stain was left on my fingertips along with an awful lingering smell， but there was no stinger or mark to suggest that I had been stung. Alarm soon turned into elation， as I realised that I had just chanced upon my first bombardier beetle， along with one of nature’s most remarkable events.

“哎喲！”我驚叫起來，手指被灼傷了，帶著火辣辣的感覺。隨著它尾部發出尖利的“噗”一聲，還噴出一團煙霧，這只步甲消失在附近的草叢深處。我的指尖上留下了一個棕色的印子，還伴著久久不散的臭味，但沒有螫針或蜇痕顯示我被叮咬。當意識到我剛才是第一次巧遇氣步甲，還親歷了自然界最令人矚目的事件之一時，這一驚嚇迅速轉化為狂喜。

What had happened was a series of extremely complex chemical reactions： the beetle first secreted a fuel and an oxidant into a reservoir chamber， which formed an inert mixture for ease of storage. When I picked it up， a small amount of this mixture was released into a sturdy reaction chamber， which was capable of tolerating high temperatures. The walls of this chamber were lined with enzymes， which triggered a violent reaction within the mixture to form a boiling solution close to 100 degrees Celsius. The massive pressure generated from the heat forced shut the valves leading into the reaction chamber， thus protecting the beetle’s internal organs from the ‘backfire’， and exited through the rear as a controlled explosion. The tip of the abdomen could be rotated freely and the explosion aimed at any angle， since the shortened wing cases had left the tip exposed. As if one explosion wasn’t impressive enough， this cycle was repeated at an astonishing rate of 500 pulses per second—yes， that squeaky ‘pop’ was in fact the sound of over seventy individual explosions！ Even with modern technology， the firing speed of our weapons truly pales in comparison to this biological machine gun.

剛才發生的是一系列極其復雜的化學反應：這只甲蟲首先分泌出燃料和氧化劑進入它的“儲存艙”，形成一種惰性混合物以便儲存。當我抓起氣步甲時，少量的混合物會被釋放進堅固的反應囊里，反應囊能耐受高溫。囊壁上成排的生物酶在混合物里會催化強烈的化學反應，形成接近攝氏100度的沸騰溶液。由熱量產生的巨大壓力迫使通向反應囊的閥門關閉，以此保護氣步甲的內臟免于“逆火”燒灼，而溶液則從尾部噴出，形成可操控的爆炸。由于縮短了的鞘翅能讓腹部尖端暴露，氣步甲的腹尖可以任意旋轉，使爆炸瞄向任何角度。好像一次爆炸不足以讓人印象深刻似的，這個循環能以令人瞠目結舌的每秒鐘500次的脈沖重復進行——是的，那噗噗響的“爆破聲”實際上是超過70次單獨爆炸的聲音！即便以現代技術衡量，人類武器開火的速度與這生物機槍相比，也實在是黯然失色。

（轉載自《叢林瑰寶——一個自然學家的探險筆記》，電子工業出版社，2020）

* 昆蟲學家，畫家。曾于劍橋大學獲自然科學學士學位，于英國帝國理工大學獲分子分類學碩士學位，其間曾赴德國馬克斯·普朗克研究所參與生態學項目研究。本文節選自《叢林瑰寶——一個自然學家的探險筆記》，該書表達了作者自幼以來對昆蟲和自然的摯愛。

** 曾于中國人民大學法學院獲法學學士、法學碩士學位，于英國倫敦大學卡斯商學院獲理學碩士學位。曾在美國、新西蘭、英國及中國香港等地工作多年，現就職于國內某金融機構。