推荐回答(4个)
昆虫的种类不同,习性不同,生活的场所也不同。为了造应不同的生活环境,足的形状发生了很大的变化,其功能也从单一的行走功用逐渐发展为具有多种功能的器官(各种足的图仿彩万志)。
①步行足:在地下跑的步行虫,虽然有翅但已不善于飞翔,为了适应其生活上的需要,经过长时期的演变,六条腿变得又细又长,跑起路来十分快速,这种足叫做步行足。当然昆虫中最基本的也是最常见的还是步行足,它们的外形细长;各节也没发生显著的变化,最适于担负行走的功用,如瓢虫、步行虫、天牛等。
②跳跃足:蝗虫、蟋蟀、蚤蝼、跳甲等昆虫十分善跳;它们的后足腿节膨大,内有发达的肌肉,可以控制胫节的屈伸,产生跳跃行为。捕捉这些昆虫时特别需要手疾眼快,否则它们会在一瞬间消失得无影无踪。昆虫中的跳高冠军非跳蚤莫属,它们跳跃的高度,可超过其体长100多倍,可以想象,假如人类能够跳过自身身高的100倍,那么,现存的世界跳高记录简直就不足挂齿了。
③捕捉足:螳螂、猎蝽等捕食性昆虫是一类益虫,不吃庄稼,专门靠捕食小动物生活,它们从卵里孵出来就有一对刀状的前足。这种前足的基节延长,腿节腹面有槽,胫节可以折嵌到腿节的槽中,腿节和肠节上还常装备着锐刺,是捕捉猎物的有力武器。当它捕获猎物时,可以利用腿节和胫节把要吃的东西夹住,再利用胫节内侧和腿节外侧锐利的刺将猎物撕碎吃掉,这种足叫捕捉足。
④开掘足:蝼蛄要在土里生活,挖筑隧道,偷吃庄稼的根、茎,那么它们是怎样钻到地里的呢?原来它们的前足又粗又壮,上面还有几个大齿,象是专门挖土的铲子,掘起土来十分方便,这种足叫做开倔足。
⑤携粉足:蜜蜂每天忙忙碌碌,来回穿梭在花丛中采集花粉和花蜜。它们用什么携带呢?经过长期的适应,它们的后足胫节特化得又宽又扁,上面有长毛相对环抱,专门用来携带花粉,被称作花粉篮。它的基节也有了专门的用处,比一般昆虫的基节要大,内面有10~12排横列的硬毛,用来梳刮在身体上的花粉。当辛勤的采集劳动结束后。一群群小蜜蜂满载花粉而归。这种足叫做携粉足。
⑥游泳足:龙虱、仰蝽等生活在水中的昆虫,能捕捉鱼苗作为食料,是养渔业的大害。鱼在水中游得够快了,它们怎么能追上鱼呢?原来龙虱、仰蝽的身体接近流线型,很象只快速潜艇,中足和后足又长又扁,向里的一面还长着一排整齐的长毛,这四条腿就象四只划船用的桨,这样游起来就很快了。这种足叫做游泳足。
⑦抱握足:如雄性龙虱的前足附节特别膨大,上面还有吸盘状的构造,交配时用以挟持雌虫,这种足称为抱握足。
⑧攀缘足:生活在毛发上的虱类,跗节只有1节,最末一节为一大型钩状的爪,胫节肥大,外缘有一指状的突起。当爪向内弯曲时,尖端可与胫节端部的指状突起密接,构成钳状的构造,牢牢地夹住寄主的毛发。这种足叫做攀缘足。
有的昆虫足已发生变化,派作它用。如
跳蚤、蝗虫的的后足膨大特化成跳跃足;
螳螂的前足像一把刀,为捕捉足;
蝼蛄的前足像把铲子,为挖掘足;
龙虱的足象船桨,为游泳足。
这就是昆虫为了生存所做的适应性变异。
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