Worms that burrow into your skin are the stuff that nightmares are made of, yet approximately one billion people across the globe are infected with parasitic round worms that enter the body this way. They belong to a group of parasites known as soil-transmitted helminths and their tiny infective larvae have developed sophisticated foraging strategies that are appropriate for their specific hosts; either cruising in search of hosts or waiting to ambush them andusing olfactory cuesproduced by their hosts.

强层stercoralis是一种感染人类的​​皮肤渗透线虫strongyloidiasis.

它有一个全球分布but is most common in rural areas of the tropics and semi tropics in communities where sanitation is poor and faecal material can contaminate the ground or the water supply. In the US, outbreaks of strongiloidiasis have been associated with institutionalised populations and veterans returning from tropical regions. Behaviours that put people in endemic areas at risk include赤脚行走，与人类的粪便材料和耕种和采矿等职业接触。幼虫也可以通过像床衣服甚至淋浴间的纺织品传播。

穿透皮肤后，传染性幼虫在血液中携带到肺部。然后，他们咳嗽到喉咙中吞咽。他们钻入小肠和换羽的衬里两次成为成年女性。肠中的雌性蠕虫会产生卵，而无需交配，这是一种被称为孤雌生成的现象。这些卵在小肠中孵化，幼虫被粪便排出。然后，他们可以通过2个换羽来产生感染性少年，穿透皮肤阶段，或者发展成自由活着的成年人，交配并产生卵，最终引起感染性少年。

S. stercoralis有一个particularly complex life cycle因为它也可能引起持续多年的自身感染。如果从小肠中从卵中孵化的幼虫穿透了肠粘膜，进入血液流并经历与母亲相同的旅程，则会发生这种情况。

Michelle Castelletto, Elissa Hallem and colleagues have recently published全面研究的结果比较这些土壤中的某些蠕虫用来寻找宿主的多种策略。他们的实验工作集中于str。stercoralis和两个大鼠寄生虫，浓氧化物rattiandNippostrongylus brasiliensisand compared their host-seeking behaviour with two nematodes that actively invade insects (entomopathogenic), one that is passively ingested by sheep or goats (Haemonchus contortus）and the free livingCaenorhabditis elegans.

By watching infective larvae placed on agar plates they were able to identify the well characterised host seeking strategy known as cruising; the human parasite being the most active and having a higher basal speed that the others. The crawling speed of this skin-penetrating nematode increased significantly at 37°C and movement tracks changed from being straight to being highly curved. In contrast, the passively ingested nematode deployed an ambush strategy, was far less active than the skin-penetrating nematodes and did not respond to thermal stimulation.

These researchers suggest crawling behaviour is adapted to the behaviour of the specific hosts; infection of rodents would occur near the host’s nests, thus requiring less mobility, whilst rapid mobility may be required to infect highly mobile humans and, being passively ingested, host seeking activity was not required ofH. Contortus。

众所周知，一些线虫幼虫站在尾巴上并在空中挥动头，以促进试图依附于传递宿主的行为，这种行为被称为刺激（在视频中看到C. elegans在这个链接). The actively invading,Steinemema carpocapsae，一种具有伏击行为的昆虫病线虫，比强层species andH. contortusdid not display this behaviour at all.

A chemotaxis assay testing 36 different odourants showed thatstr。stercoraliswas attracted to an array of human skin and sweat odours which also attracted human-biting mosquitoes, whereas CO₂was not found to be an attractant. Responses by 6 other species appeared to suggest they responded to specific host cues.

Interestingly,H. contortus被草和co的气味所吸引₂那将出现在宿主的呼吸中，并被许多皮肤和汗水剂所击退。该线虫的第一阶段和第二阶段的幼虫以粪便中的细菌为食，随着生命周期的发展，它们从粪便迁移到了可能被牧场上放牧的绵羊或山羊意外摄入的位置。因此，对不同的配音剂的响应str。stercoralis可能有利于成功的摄入而不是皮肤穿透。

最后，幼虫和成年蠕虫在生命周期的自由生活替代阶段str。stercoraliswere strongly attracted to the odour of host faeces, where they reside, but the infective, skin-penetrating juveniles were not.

作者承认，他们记录的行为可能取决于底物，并且如果对不同底物进行监测的感染性幼虫可能会有所不同。但是，他们得出的结论是，觅食行为和对异形的反应的相似性似乎反映了宿主的特异性，而不是不同的线虫物种的紧密关系。

If you want to avoid cruising worms encountering your bare feet when travelling in endemic areas the best thing to do is to foil their host seeking behaviour by wearing robust sandals or shoes.